Magnetic sensing element having chromium layer between antiferromagnetic layers

A magnetic sensing element comprising a composite film having a center portion and two side portions, a second antiferromagnetic layer, a chromium nonmagnetic layer, and third antiferromagnetic layers is provided. The composite film comprises a first antiferromagnetic layer; a pinned magnetic layer on the first antiferromagnetic layer; a nonmagnetic material layer on the pinned magnetic layer; and a free magnetic layer on the nonmagnetic material layer. The second antiferromagnetic layer is disposed on the free magnetic layer. The chromium nonmagnetic layer is disposed on the second antiferromagnetic layer at the center portion. The third antiferromagnetic layers are disposed on the second antiferromagnetic layer at the two side portions. The magnetization direction in the two side portions of the free magnetic layer is pinned in the track width direction and the magnetization direction in the center portion is rotatable in response to external magnetic fields.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to magnetic sensing elements for use in hard disk devices and magnetic sensors. In particular, it relates to a magnetic sensing element having excellent read characteristics that can adequately control the magnetization of free magnetic layers even with narrower tracks and to a method for fabricating the same.

2. Description of the Related Art

FIG. 36is a partial cross-sectional view of a conventional magnetic sensing element viewed from the face that opposes a recording medium. Hereinafter, this face is referred to as the “opposing face”.

Referring toFIG. 36, a composite film108is formed on a substrate101. The composite film108is constituted from an antiferromagnetic layer102, a pinned magnetic layer103, a nonmagnetic material layer104, and a free magnetic layer105. A hard bias layer106is disposed at each side of the composite film108. An electrode layer107is formed on each hard bias layer106.

The magnetization of the pinned magnetic layer103is pinned in the Y direction in the drawing by an exchange coupling magnetic field generated between the pinned magnetic layer103and the antiferromagnetic layer102. The magnetization of the free magnetic layer105is oriented in the X direction in the drawing by a longitudinal bias magnetic field.

As shown inFIG. 36, the track width Tw is determined by the width of the free magnetic layer105in the track width direction (the X direction). The track width Tw is becoming ever smaller as recording densities become higher.

However, the magnetic sensing element having the structure shown inFIG. 36cannot properly control the magnetization direction of the free magnetic layer105when the track width is small.

First, according to the structure shown inFIG. 36, the width of the free magnetic layer105must be decreased to read narrower tracks. As the track becomes narrower, regions in the free magnetic layer105affected by strong longitudinal bias magnetic fields from the hard bias layers106occupy large portions of the free magnetic layer105. The regions affected by the strong longitudinal bias magnetic fields then form dead regions that do not readily respond to external magnetic fields. Since the dead regions relatively expand, the sensitivity of the magnetic sensing element is degraded as the tracks become narrower.

Secondly, the hard bias layer106may easily become magnetically discontinuous from the free magnetic layer5. This problem is particularly acute when a bias underlayer composed of Cr is provided between the hard bias layer106and the free magnetic layer105.

Such magnetic discontinuity intensifies the adverse effects of demagnetizing fields at the two ends of the free magnetic layer105in the track width direction, often resulting in a magnetization disturbance in the free magnetic layer105, i.e., a buckling phenomenon. The buckling phenomenon occurs more frequently over large areas in the free magnetic layer105as the track becomes narrower. This results in instability in the read waveform.

Thirdly, as the gap becomes narrower, part of the longitudinal bias magnetic fields from the hard bias layers106escapes to shield layers (not shown) disposed above and below the magnetic sensing element shown in FIG.36. This disturbs the magnetization state of the shield layers and weakens the longitudinal bias magnetic field supplied to the free magnetic layer105. Thus, the magnetization of the free magnetic layer105cannot be properly controlled.

Recently, in order to overcome these problems, exchange bias methods are beginning to be employed to control the magnetization of the free magnetic layer105. One exchange bias method provides an antiferromagnetic layer disposed on a free magnetic layer.

A magnetic sensing element of an exchange bias type is manufactured, for example, through the steps shown inFIGS. 37 and 38.FIGS. 37 and 38are partial cross-sectional views of the magnetic sensing element viewed from the opposing face.

In the step shown inFIG. 37, an antimagnetic layer2composed of a PtMn alloy is formed on a substrate1. Then a pinned magnetic layer3composed of a magnetic material, a nonmagnetic material layer4, and a free magnetic layer5composed of a magnetic material are deposited on the antimagnetic layer2. A Ta film9for preventing oxidation of the free magnetic layer5when exposed to air is formed on the free magnetic layer5.

As shown inFIG. 37, a lift-off resist layer10is then formed on the Ta film9. Part of the Ta film9not covered with the resist layer10is completely removed by ion milling. At this time, part of the free magnetic layer5under the Ta film9is also removed. The removed portion is indicated by broken lines in the drawing.

Next, in the step shown inFIG. 38, a ferromagnetic layer11, a second antiferromagnetic layer12composed of an IrMn alloy, and an electrode layer13are sequentially formed on each of the exposed portions of the free magnetic layer5at the two sides of the resist layer10. The liftoff resist layer10is removed at the end to complete the exchange bias magnetic sensing element.

In the magnetic sensing element shown inFIG. 38, the track width Tw is determined by the gap between the ferromagnetic layers11in the track width direction (the X direction in the drawing). The magnetization directions of the ferromagnetic layers11are firmly pinned in the X direction in the drawing by exchange coupling magnetic fields generated between the ferromagnetic layers11and the second antiferromagnetic layers12. As a result, two side portions A of the free magnetic layer5located under the ferromagnetic layers11are strongly magnetized in the X direction by ferromagnetic coupling with the ferromagnetic layers11. On the other hand, the central portion B of the free magnetic layer5in the track width Tw region is only weakly magnetized to be in a single magnetic domain state such that the magnetization of the central portion B can rotate in response to external magnetic fields.

The exchange bias magnetic sensing element manufactured through the steps shown inFIGS. 37 and 38, however, has the following problems.

First, during the ion milling in the step shown inFIG. 37, not only the Ta film9but also part of the free magnetic layer5is removed. Moreover, inert gas, such as Ar, used during the ion milling readily enters the free magnetic layer5. This damage in the free magnetic layer5destroys the crystal structure in surface portions5aof the free magnetic layer5and causes lattice defects (a so-called mixing effect). As a result, the magnetic characteristics of the surface portions5aof the free magnetic layer5are often degraded.

Ideally, only the Ta film9is removed during ion milling in the step shown inFIG. 37without removing the free magnetic layer5. However, in practice, it is difficult to control the milling operation in such a manner because of the thickness of the Ta film9. The Ta film9is formed to have a thickness of approximately 30 to 50 Å. Such a large thickness is required to properly prevent the oxidation of the free magnetic layer5.

When the Ta film9is exposed to air or field-annealed to generate exchange coupling magnetic fields between the pinned magnetic layer3and the ferromagnetic layer11and between the antimagnetic layer2and the second antiferromagnetic layer12, the oxidized portion expands, and the entire thickness of the Ta film9becomes larger than that immediately after deposition. For example, a Ta film9having a thickness of approximately 30 Å immediately after deposition may expand to approximately 45 Å in thickness by the oxidation.

In order to effectively mill the Ta film9expanded by the oxidation, high-energy is required. Since high-energy ion milling has a high milling rate, it is almost impossible to stop milling at the moment the Ta film9is completely removed. In other words, when the energy is high, the margin of position for stopping the milling must be set large. Accordingly, part of the free magnetic layer5under the Ta film9is removed, and significant damage is inflicted on the free magnetic layer5by high-energy ion milling, resulting in degradation of the magnetic characteristics.

Secondly, it is difficult to stop ion milling partway of the free magnetic layer5shown inFIG. 37because the free magnetic layer5is formed to have a thickness of 30 to 40 Å and is milled using high energy. In the worst case, the two side portions A of the free magnetic layer5may be completely removed by ion milling. As described above, because the thickness of the free magnetic layer5is small, it is difficult to stop ion milling partway of the free magnetic layer5.

Thirdly, the surface of the free magnetic layer5exposed to the ion milling exhibits degraded magnetic characteristics due to the damage inflicted by the milling. Thus, the magnetic coupling (ferromagnetic exchange interaction) between the free magnetic layer5and the ferromagnetic layers11is insufficient. As a result, the thickness of the ferromagnetic layers11must be increased.

However, when the thickness of the ferromagnetic layers11is increased, the exchange coupling magnetic fields with the second antiferromagnetic layers12become weak. As a result, the magnetization of the two side portions A of the free magnetic layer5cannot be firmly pinned. This causes a problem of side reading. The resulting magnetic sensing element cannot properly meet the demand for narrower tracks.

Moreover, when the thickness of the ferromagnetic layers11is excessively large, static magnetic fields from ends of the ferromagnetic layers11may readily reach the central portion B of the free magnetic layer5, thereby degrading the sensitivity of the central portion B, which has a rotatable magnetization in response to external magnetic fields.

As described above, it has been impossible to manufacture a magnetic sensing element that can meet the demand for narrower tracks through the above-described steps of milling the two side portions of the Ta film9to expose the free magnetic layer5and depositing the ferromagnetic layers11and the second antiferromagnetic layers12on the exposed portions of the free magnetic layer5. This is because the magnetization of the free magnetic layer5cannot be properly controlled in this structure.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide an exchange-bias magnetic sensing element that can properly control the magnetization of a free magnetic layer and that can meet the trend for narrower tracks.

A first aspect of the present invention provides a magnetic sensing element comprising a composite film having a center portion and two side portions, a second antiferromagnetic layer, a chromium nonmagnetic layer, and third antiferromagnetic layers. The composite film comprises a first antiferromagnetic layer; a pinned magnetic layer on the first antiferromagnetic layer; a nonmagnetic material layer on the pinned magnetic layer; and a free magnetic layer on the nonmagnetic material layer. The second antiferromagnetic layer is disposed on the free magnetic layer. The chromium nonmagnetic layer is disposed on the second antiferromagnetic layer at the center portion. The third antiferromagnetic layers are disposed on the second antiferromagnetic layer at the two side portions.

According to this structure, the magnetization directions of the two side portions of the free magnetic layer can be properly pinned in the track width direction by exchange coupling magnetic fields with the antiferromagnetic layers. The center portion of the free magnetic layer is moderately put in a single-magnetic-domain state so that the center portion can respond to external magnetic fields.

The chromium nonmagnetic layer on the second antiferromagnetic layer at the center portion protects the second antiferromagnetic layer from oxidation by exposure to air. The chromium nonmagnetic layer may extend between the second antiferromagnetic layer and each of the third antiferromagnetic layers.

Since the free magnetic layer is covered by the second antiferromagnetic layer, the free magnetic layer does not suffer from damage inflicted by ion milling.

The chromium nonmagnetic layer is a dense layer, and the oxidation rarely progresses in the thickness direction when exposed to air. The thickness of the chromium nonmagnetic layer need not be large to protect the underlying layers from oxidation. Thus, low-energy ion milling can be employed, and a magnetic sensing element that can effectively be used with narrow tracks can be manufactured. Moreover, with the chromium nonmagnetic layer, the exchange coupling magnetic field (Hex) between the second antiferromagnetic layer and the free magnetic layer can become larger.

When the chromium nonmagnetic layer is provided between the second antiferromagnetic layer and each of the third antiferromagnetic layers, the thickness of the chromium nonmagnetic layer is preferably larger in the center portion than in the two side portions.

Preferably, the average thickness of the chromium nonmagnetic layer in the two side portions is 3 Å or less. The average thickness of the chromium nonmagnetic layer in the two side portions may be in the range of 0.2 to 1.0 Å. Moreover, the third antiferromagnetic layers may be in contact with the second antiferromagnetic layer without the chromium nonmagnetic layer therebetween.

With a chromium nonmagnetic layer having a thickness of 3 Å or less, an antiferromagnetic interaction easily occurs between the second antiferromagnetic layer and the third antiferromagnetic layer at the two side portions. Thus the second antiferromagnetic layer and the third antiferromagnetic layer function as one antiferromagnetic layer that properly firmly pin the magnetization directions of the two side portions of the free magnetic layer.

Preferably, the thickness of the chromium nonmagnetic layer is in the range of 2 to 10 Å, and more preferably in the range of 2 to 5 Å in the center portion.

Preferably, the second antiferromagnetic layer is nonantiferromagnetic in the center portion and antiferromagnetic in the two side portions.

When the center portion of the second antiferromagnetic layer is nonantiferromagnetic, it rarely transforms into an ordered structure by field annealing. Thus, no exchange coupling magnetic field is generated between the second antiferromagnetic layer and the free magnetic layer at the center portion, and the magnetization direction of the center portion of the free magnetic layer is not firmly pinned in a certain direction. Since the second antiferromagnetic layer and the third antiferromagnetic layers function as one layer, the second antiferromagnetic layer at the two side portions easily transforms into ordered structures by field annealing. Exchange coupling magnetic fields are thus generated between the second antiferromagnetic layer and the free magnetic layer in the two side portions so as to firmly pin the magnetization directions at the two side portions of the free magnetic layer in the track width direction.

Preferably, the thickness of the second antiferromagnetic layer is in the range of 5 to 50 Å, more preferably in the range of 10 to 50 Å, and most preferably in the range of 30 to 40 Å. At such a thickness, the exchange coupling magnetic field between the second antiferromagnetic layer and the free magnetic layer at the center portion is small, if any.

A second aspect of the present invention provides a magnetic sensing element comprising a composite film having a center portion and two side portions, second antiferromagnetic layers, chromium nonmagnetic layers, and third antiferromagnetic layers. The composite film comprises a first antiferromagnetic layer; a pinned magnetic layer on the first antiferromagnetic layer; a nonmagnetic material layer on the pinned magnetic layer; and a free magnetic layer on the nonmagnetic material layer. The second antiferromagnetic layers are disposed on the free magnetic layer at the two side portions. The chromium nonmagnetic layers are disposed on the second antiferromagnetic layers. The third antiferromagnetic layers disposed on the chromium nonmagnetic layers.

The magnetic sensing element according to the second aspect of the present invention differs from that according to the first aspect of the present invention in that the chromium nonmagnetic layer is always provided between the second antiferromagnetic layer and the third antiferromagnetic layer. No second antiferromagnetic layer needs to be provided at the center portion. Such differences are derived from the difference in fabrication processes.

According to the second aspect of the present invention, the second antiferromagnetic layer and the third antiferromagnetic layer are stacked on the free magnetic layer at each of the two side portions. The second and third antiferromagnetic layers function as one antiferromagnetic layer. The magnetization directions of the free magnetic layer at the two side portions are firmly pinned in the track width direction by the exchange coupling magnetic fields between the free magnetic layer and the second antiferromagnetic layer at the two side portions. The center portion of the free magnetic layer is only moderately put in a single-magnetic-domain state so that the magnetization direction thereof can rotate in response to external magnetic fields.

Since the two side portions of the free magnetic layer are covered with the second antiferromagnetic layer, they are not affected by milling.

Alternatively, the second antiferromagnetic layers may extend to the center portion so as to be connected to each other. In this manner, the entire upper face of the free magnetic layer can be protected by the second antiferromagnetic layers during ion milling.

Moreover, the chromium nonmagnetic layers may also extend to the center portion to be connected to each other.

Preferably, the second antiferromagnetic layers are nonantiferromagnetic in the center portion and antiferromagnetic in the two side portions. According to this structure, no exchange coupling magnetic field is generated between the second antiferromagnetic layer and the free magnetic layer at the center portion, and the magnetization direction of the center portion of the free magnetic layer remains rotatable. Since the second antiferromagnetic layer and the third antiferromagnetic layers function as one layer, the second antiferromagnetic layer at the two side portions easily transforms into ordered structures by field annealing. Exchange coupling magnetic fields are thus generated between the second antiferromagnetic layer and the free magnetic layer in the two side portions so as to firmly pin the magnetization directions at the two side portions of the free magnetic layer in the track width direction.

Alternatively, the third antiferromagnetic layers may extend to the center portion so as to be connected to each other; the thickness of the third antiferromagnetic layers may be smaller in the center portion than in the side portions; and the third antiferromagnetic layers may be nonantiferromagnetic in the center portion.

Preferably, the thickness of the second antiferromagnetic layers is 50 Å or less in the center portion. At such a thickness, the exchange coupling magnetic field between the antiferromagnetic layers and the free magnetic layer at the center portion is small, if any. Preferably, no antiferromagnetic layer is formed on the free magnetic layer in the center portion.

More preferably, the thickness of the antiferromagnetic layers formed on the center portion of the free magnetic layer is 40 Å or less.

Preferably, the thickness of the chromium nonmagnetic layers is in the range of 0.2 to 3 Å in the two side portions. More preferably, the thickness of the chromium nonmagnetic layers is in the range of 0.2 to 1.0 Å in the two side portions.

At a such thickness, an antiferromagnetic interaction occurs between the second antiferromagnetic layers and the third antiferromagnetic layers, and the second and third antiferromagnetic layers function as one antiferromagnetic layer that properly pins the magnetization directions of the two side portions of the free magnetic layer in the track width direction.

The magnetic sensing element of the present invention preferably further comprises a noble metal layer disposed between each nonmagnetic layer and the corresponding second antiferromagnetic layer.

When the chromium nonmagnetic layer is deposited directly on the second antiferromagnetic layer, transformation into ordered structures occurs even though the thickness of the second antiferromagnetic layer is small. As a result, the exchange coupling magnetic field between the second antiferromagnetic layer and the free magnetic layer28readily increases, and the amount of change in magnetization direction in response to external magnetic fields readily decreases. By providing the noble metal layer between the chromium nonmagnetic layer and the second antiferromagnetic layer, the tendency of the second antiferromagnetic layer to transform into ordered structures can be adequately controlled. Thus, a decrease in the rate of change in resistance can be avoided.

The noble metal layer preferably contains at least one element selected from the group consisting of Ru, Re, Pd, Os, Ir, Pt, Au, and Rh.

Preferably, the free magnetic layer comprises three magnetic sublayers. In particular, the three magnetic sublayers preferably comprise CoFe, NiFe, and CoFe, respectively.

The magnetic sensing element of the present invention may further include electrode layers on the third antiferromagnetic layers so that an electric current flows in a direction parallel to the surface of each layer of the composite film. This type of magnetic sensing element is called “current-in-the-plane (CIP) magnetic sensing element”.

Alternatively, the magnetic sensing element of the present invention may include an upper electrode layer disposed over the center portion of the composite and the third antiferromagnetic layers; and a lower electrode layers disposed at the bottom of the composite film, wherein an electric current flows in a direction perpendicular to the surface of each layer of the composite film. This type of magnetic sensing element is called “current-perpendicular-to-the-plane (CPP) magnetic sensing element”.

Preferably, the nonmagnetic material layer is made of a nonmagnetic conductive material. In such a case, the resulting magnetic sensing element is a spin-valve giant magnetoresistive (GMR) element of either a CIP type or a CPP type.

Alternatively, the nonmagnetic material layer may be made of an insulating material. In such a case, the resulting magnetic sensing element is a spin-valve tunneling magnetoresistive element (CPP-TMR).

In the present invention, the second antiferromagnetic layer is preferably made of a PtMn alloy, an X—Mn alloy, or a Pt—Mn—X′ alloy, wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, and X′ is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr.

These alloys immediately after deposition have a disordered face-centered cubic (fcc) structure and transform into an ordered face-centered tetragonal (fct) structure of a CuAuI type by annealing. As a result, a large exchange coupling magnetic field can be generate at the interface with the ferromagnetic layer.

The chromium nonmagnetic layer of the present invention promotes the transformation of these alloys into ordered structures.

When a laminate including the free magnetic layer, the second antiferromagnetic layer composed of one of these alloys, and the third antiferromagnetic layer is annealed, the PtMn alloy, the X—Mn alloy, or the Pt—Mn—X′ alloy transforms into an ordered structure. However, the region around the interface between the antiferromagnetic layer and the free magnetic layer rarely undergoes the transformation into ordered structures. When the chromium nonmagnetic layer is provided on the second antiferromagnetic layer, the transformation into ordered structure around interface is promoted, thereby increasing the magnitude of the exchange coupling magnetic field at the interface.

In the present invention, the crystal structure of the second antiferromagnetic layer is, for example, of a CuAuI type. Chromium atoms diffusing from the nonmagnetic layer partly replace the lattice points of the crystal lattice constituted from atoms of Pt and Mn, the crystal lattice constituted from atoms of X and Mn, or the crystal lattice constituted from atoms of Pt, Mn, and X′.

The present invention also provides a method for fabricating the magnetic sensing element. The method comprises (a) depositing a first antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic material layer, a free magnetic layer, a second antiferromagnetic layer, and a chromium nonmagnetic layer on a substrate so as to form a composite on the substrate; (b) field-annealing the composite to generate an exchange coupling magnetic field between the first antiferromagnetic layer and the pinned magnetic layer so as to pin the magnetization direction of the pinned magnetic layer in the height direction; (c) forming a resist layer on the center of the chromium nonmagnetic layer, and partially milling the two side portions of the chromium nonmagnetic layer not covered by the resist; (d) forming a third antiferromagnetic layer on each of the two side portions of the chromium nonmagnetic layer and removing the resist layer; and (e) field-annealing the composite and the third antiferromagnetic layers to generate exchange coupling magnetic fields between the second antiferromagnetic layer and the free magnetic layer at the two side portions so as to pin the magnetization directions of the two side portions of the free magnetic layer in a direction orthogonal to the magnetization direction of the pinned magnetic layer.

In step (a) above, the layers from the first antiferromagnetic layer to the chromium nonmagnetic layer are sequentially deposited on the substrate. In step (c) above, the two side portions of the chromium nonmagnetic layer are only partially milled. By leaving part of the chromium nonmagnetic layer on each of the two side portions of the chromium nonmagnetic layer, the second antiferromagnetic layer can be protected from damage inflicted by ion milling. Moreover, because the thickness of the chromium nonmagnetic layer is small at the two side portions, the third antiferromagnetic layer and the second antiferromagnetic layer can function as one antiferromagnetic layer. As a result, the magnetization direction in the two side portions of the free magnetic layer can be properly pinned in the track width direction by the exchange coupling magnetic field between the free magnetic layer and the second antiferromagnetic layer at the two side portions. The center portion of the free magnetic layer is not as firmly magnetized as in the side portions, and the magnetization direction thereof can rotate in response to external magnetic fields.

According to this method, the free magnetic layer is not affected by ion milling. Thus, the magnetization directions of the two side portions of the free magnetic layer can be firmly pinned while the magnetization direction of the center portion is rotatable in response to external magnetic fields. Thus, the magnetization direction of the free magnetic layer can be properly controlled.

Because the chromium nonmagnetic layer is provided, the exchange coupling magnetic field (Hex) between the second antiferromagnetic layer and the free magnetic layer is larger than when a nonmagnetic layer of other material is provided. Thus, the magnetization directions of the two side portions of the free magnetic layer can be firmly pined by the two side portions of the second antiferromagnetic layer, and side reading can be reduced.

According to this method, a magnetic sensing element with few errors due to side reading having high sensitivity and superior read characteristics even with narrower tracks can be fabricated.

Preferably, in step (c) above, the thickness of the two side portions of the chromium nonmagnetic layer is in the range of 0.2 to 3 Å (average thickness), and more preferably 0.2 to 1.0 Å.

At such a thickness, an antiferromagnetic interaction can be produced between the third antiferromagnetic layers and the second antiferromagnetic layer made in step (d). As a result, the third and second antiferromagnetic layers can function as one antiferromagnetic layer, and the magnetization directions of the two side portions of the free magnetic layer can be properly pinned in the track width direction. Moreover, the second antiferromagnetic layer is not significantly damaged by ion milling.

In step (c) above, the two side portions of the chromium nonmagnetic layer not covered by the resist layer may be completely removed to expose the two side portions of the second antiferromagnetic layer, and the third antiferromagnetic layers may be formed on the exposed portions of the second antiferromagnetic layer in step (d).

In step (a) above, the thickness of the second antiferromagnetic layer is preferably in the range of 5 to 50 Å, more preferably 10 to 50 Å, and most preferably 30 to 40 Å.

In the present invention, the thickness of the second antiferromagnetic layer must not be large. If the second antiferromagnetic layer is thick, it easily transforms into an ordered structure by field annealing, and a large exchange coupling magnetic field is generated between the free magnetic layer and the second antiferromagnetic layer at the center portions.

Accordingly, the thickness of the second antiferromagnetic layer is adjusted as above to prevent generation of a large exchange coupling magnetic field between the center portions of the free magnetic layer and the second antiferromagnetic layer.

In step (a) above, the thickness of the chromium nonmagnetic layer is preferably in the range of 2 to 10 Å, and more preferably 2 to 5 Å. At such a thickness, the thickness of the chromium nonmagnetic layer can be easily adjusted by employing low-energy ion milling in step (c). As a result, the second antiferromagnetic layer does not suffer from damage inflicted by the ion milling.

The present invention also provides another method for fabricating the magnetic sensing element. The method comprises (f) depositing a first antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic material layer, a free magnetic layer, a second antiferromagnetic layer, and a chromium nonmagnetic layer on a substrate so as to form a composite on the substrate; (g) field-annealing the composite to generate an exchange coupling magnetic field between the first antiferromagnetic layer and the pinned magnetic layer so as to pin the magnetization direction of the pinned magnetic layer in the height direction; (h) partly milling the surface of the chromium nonmagnetic layer; (i) forming a third antiferromagnetic layer on the chromium nonmagnetic layer; (j) forming a mask layer on the two side portions of the third antiferromagnetic layer and milling the center portion of the third antiferromagnetic layer not covered by the mask layer; and (k) field-annealing the composite and the third antiferromagnetic layer to generate exchange coupling magnetic fields between the second antiferromagnetic layer and the free magnetic layer at the two side portions so as to pin the magnetization directions of the two side portions of the free magnetic layer in a direction orthogonal to the magnetization direction of the pinned magnetic layer.

In step (f) above, the layers from the first antiferromagnetic and the chromium nonmagnetic layer are sequentially deposited on the substrate. In step (h), the chromium nonmagnetic layer is only partly milled. Thus, the underlying second antiferromagnetic can be protected from damage inflicted by ion milling. Moreover, since the thickness of the chromium nonmagnetic layer is small, the third antiferromagnetic layer and the second antiferromagnetic layer can function as one antiferromagnetic layer by an antiferromagnetic interaction therebetween.

In step (j) above, the thickness of the center portion of the third antiferromagnetic layer is reduced by milling. In this manner, the magnetization directions of the two side portions of the free magnetic layer can be properly pinned in the track width direction by exchange coupling magnetic fields with the second antiferromagnetic layer. The magnetization direction in the center portion of the free magnetic layer is rotatable in response to external magnetic fields.

According to the above method, the free magnetic layer is not affected by ion milling. Thus, a sufficient longitudinal bias magnetic field can be provided at two side portions of the free magnetic layer, and the magnetization of the free magnetic layer can be properly controlled.

According to this method, a magnetic sensing element having high sensitivity and superior read characteristics even with narrower tracks can be fabricated.

Preferably, in step (f) above, the thickness of the chromium nonmagnetic layer is in the range of 5 to 50 Å, more preferably 10 to 50 Å, and most preferably 30 to 40 Å. At such a thickness, the center portion of the second antiferromagnetic layer rarely transforms into an ordered structure by field annealing, and no exchange coupling magnetic field is generated between the center portion of the second antiferromagnetic layer and the center portion of the free magnetic layer. Thus, the center portion of the free magnetic layer can be moderately put to a single-magnetic-domain state so that the magnetization direction thereof can rotate in response to external magnetic fields.

In step (f) above, the thickness of the chromium nonmagnetic layer is preferably 2 to 10 Å, and more preferably 2 to 5 Å. In this manner, the thickness of the chromium nonmagnetic layer can be easily adjusted by employing low-energy ion milling in step (h). As a result, the second antiferromagnetic layer does not suffer from damage inflicted by the ion milling.

In step (h), the chromium nonmagnetic layer is preferably milled to a thickness of 0.2 to 3.0 Å, and more preferably 0.2 to 1.0 Å (average thickness). At such a thickness, an antiferromagnetic interaction can be generated between the two side portions of the third antiferromagnetic layer and the second antiferromagnetic layer, and the second and third antiferromagnetic layers can function as one antiferromagnetic layer. As a result, the magnetization directions at the two side portions of the free magnetic layer can be pinned in the track width direction.

In step (j) above, part of the third antiferromagnetic not covered by the mask layer may be completely removed so as to expose the chromium nonmagnetic layer.

In step (j) above, part of the third antiferromagnetic layer not covered by the mask layer may be completely removed so as to expose the chromium nonmagnetic layer, and the exposed portion of the chromium nonmagnetic layer may also be completely removed to expose the second antiferromagnetic layer.

Moreover, step (k) of field annealing may be performed between the steps (i) and (j).

Preferably, in steps (a) and (f), a noble metal layer is provided between the second antiferromagnetic layer and the chromium nonmagnetic layer.

When the chromium nonmagnetic layer is disposed on the second antiferromagnetic layer, the second antiferromagnetic layer readily transforms to an ordered structure even when the second antiferromagnetic layer has a small thickness. This generates a large exchange coupling magnetic field between the center portions of the free magnetic layer and the antiferromagnetic layer and reduces the amount of change in magnetization direction in response to external magnetic fields. By providing the noble metal layer between the chromium nonmagnetic layer and the second antiferromagnetic layer, the transformation of the second antiferromagnetic layer into an ordered structure can be properly controlled, and a decrease in the rate of change in magnetic resistance can be prevented.

The noble metal layer preferably contain at least one element selected from the group consisting of Ru, Re, Pd, Os, Ir, Pt, Au, and Rh.

Preferably, in steps (a) and (f) above, the free magnetic layer is constituted from three magnetic sublayers. The three magnetic sublayers are preferably made of CoFe, NiFe, and CoFe, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG. 1is a partial cross-sectional view of a magnetic sensing element (spin-valve thin film element) according to a first embodiment of the present invention viewed from the face of the magnetic sensing element opposing a recording medium. Hereinafter, this face is referred to as the “opposing face”.

Referring toFIG. 1, a seed layer21composed of a NiFe alloy, a NiFeCr alloy, elemental Cr, or the like is formed on a substrate20. For example, the seed layer21is composed of (Ni0.8Fe0.2)60 at %Cr40 at %and has a thickness of 60 Å.

A first antiferromagnetic layer22is formed on the seed layer21. The first antiferromagnetic layer22is composed of a PtMn alloy, an X—Mn alloy, or a Pt—Mn—X′ alloy wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, and X′ is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr.

When the first antiferromagnetic layer22composed of any one of these alloys is annealed, an exchange coupling film that generates a large exchange coupling magnetic field consisting of the first antiferromagnetic layer22and a pinned magnetic layer23described below can be obtained. In particular, when the first antiferromagnetic layer22is composed of a PtMn alloy, the resulting exchange coupled film exhibits an exchange coupling magnetic field of at least 48 kA/m, for example, more than 64 kA/m, and has a blocking temperature of 380° C. The blocking temperature is the temperature at which the generated exchange coupling magnetic field vanishes.

These alloys immediately after deposition have a disordered face-centered cubic (fcc) structure and transform into an ordered face-centered tetragonal (fct) structure of a CuAuI type by annealing.

The thickness of the first antiferromagnetic layer22around the center in the track width direction is 80 to 300 Å.

A pinned magnetic layer23is formed on the first antiferromagnetic layer22. The pinned magnetic layer23has a synthetic ferrimagnetic structure comprising three layers, namely, a magnetic sublayer24, a nonmagnetic interlayer25, and a magnetic sublayer26.

The magnetic sublayers24and26are composed of a magnetic material, for example, a NiFe alloy, elemental Co, a CoNiFe alloy, a CoFe alloy, or a CoNi alloy. The magnetic sublayers24and26are preferably composed of the same material.

The nonmagnetic interlayer25is composed of a nonmagnetic material containing at least one of Ru, Rh, Ir, Cr, Re, and Cu. Preferably, the nonmagnetic interlayer25is composed of Ru.

A nonmagnetic material layer27is formed on the pinned magnetic layer23. The nonmagnetic material layer27prevents the pinned magnetic layer23and a free magnetic layer28described later from being magnetically coupled to each other. Since sensing current mainly flows in the nonmagnetic material layer27, the nonmagnetic material layer27is preferably composed of a conductive nonmagnetic material such as Cu, Cr, Au, or Ag. Preferably, the nonmagnetic material layer27is composed of Cu.

A free magnetic layer28is formed on the nonmagnetic material layer27. In the embodiment shown inFIG. 1, the free magnetic layer28has a two-layer structure comprising an anti-diffusion sublayer29and a magnetic material sublayer30. The anti-diffusion sublayer29is composed of Co, CoFe, or the like and prevents interdiffusion between the free magnetic layer28and the nonmagnetic material layer27. The magnetic material sublayer30is disposed on the anti-diffusion sublayer29and is composed of a NiFe alloy, for example.

A second antiferromagnetic layer31is disposed on the free magnetic layer28. As with the first antiferromagnetic layer22, the second antiferromagnetic layer31is composed of a PtMn alloy, an X—Mn alloy, or a Pt—Mn—X′ alloy, wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, and X′ is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr.

In the embodiment shown inFIG. 1, a nonmagnetic layer32is disposed on the second antiferromagnetic layer31. A third antiferromagnetic layer33is disposed on each of the two side portions32aof the nonmagnetic layer32. As with the first antiferromagnetic layer22, the third antiferromagnetic layers33are composed of a PtMn alloy, an X—Mn alloy, or a Pt—Mn—X′ alloy, wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, and X′ is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr. Preferably, the third antiferromagnetic layer33and the second antiferromagnetic layer31are composed of the same material.

An electrode layer34is disposed on each of the third antiferromagnetic layers33. The electrode layers34are composed of, for example, Au, W, Cr, Ru, or Ta.

In this embodiment, the gap between the third antiferromagnetic layers33and the gap between the electrode layers34widens along the Z direction in the drawing, as shown in FIG.1. Accordingly, ends33aof the third antiferromagnetic layers33and ends34aof the electrode layers34are formed as slopes having either flat surfaces or curved surfaces.

The features of the magnetic sensing element of this embodiment shown inFIG. 1will now be described.

As shown inFIG. 1, the second antiferromagnetic layer31is disposed on the free magnetic layer28, and the third antiferromagnetic layers33is formed on each of two side portions C of the second antiferromagnetic layer31, with the nonmagnetic layer32therebetween. The two side portions32aof the nonmagnetic layer32disposed between the second antiferromagnetic layer31and the third antiferromagnetic layers33have a small thickness. Preferably, the two side portions32ahave a thickness in the range of 0.2 to 3 Å, and more preferably 0.2 to 1.0 Å.

The nonmagnetic layer32is composed of Cr. The average thickness can be calculated by X-ray fluorescence analysis.

The average thickness of the nonmagnetic layer32is sometimes less than 1 Å. As is widely known, no uniform thin film has a thickness of less than 1 Å since 1 Å corresponds to the diameter of one atom or less. However, in a nonuniform thin film containing unevenly distributed Cr atoms, there exist regions with chromium atoms and regions without any chromium atoms. Accordingly, the average thickness of the nonmagnetic layer32is sometimes less than 1 Å. At such a thickness, ferromagnetic interaction occurs between the second antiferromagnetic layer31and the third antiferromagnetic layers33through the nonmagnetic layer32. As a result, the second antiferromagnetic layer31and the third antiferromagnetic layers33readily function as a single antiferromagnetic layer.

In view of the above, the embodiment shown inFIG. 1has a structure similar to a magnetic sensing element comprising a ferromagnetic layer with a large thickness disposed on each of the two side portions C of the free magnetic layer28. The magnetization directions of the two side portions C of the free magnetic layer28are properly pinned in the track width direction (the X direction in the drawing) by an exchange coupling magnetic field with the two side portions C of the second antiferromagnetic layer31.

In the embodiment shown inFIG. 1, the second antiferromagnetic layer31also covers a center portion D of the free magnetic layer28. However, the third antiferromagnetic layers33are not disposed over the center portion D.

In this embodiment, the thickness h1of the second antiferromagnetic layer31is controlled during deposition so that the center portion D of the second antiferromagnetic layer31does not exhibit antiferromagnetic properties and become nonantiferromagnetic or nonmagnetic instead.

The thickness h1of the second antiferromagnetic layer31is preferably in the range of 5 to 50 Å, more preferably 10 to 50 Å, and most preferably 30 to 40 Å.

Since the nonmagnetic layer32disposed on the second antiferromagnetic layer31functions as a protective layer, the antiferromagnetic characteristics at the two side portions of the second antiferromagnetic layer31during or after manufacture are prevented from being degraded. Accordingly, in this embodiment, the thickness h1of the second antiferromagnetic layer31may be 5 to 50 Å, for example, approximately 10 Å.

At such a small thickness, the center portion D of the second antiferromagnetic layer31rarely transforms into an ordered structure even after field annealing. The exchange coupling magnetic field between the center portion D of the second antiferromagnetic layer31and the center portion D of the free magnetic layer28is small, if any.

The thickness of the second antiferromagnetic layer31is at least 5 Å because, at a smaller thickness, the exchange coupling magnetic fields between the two side portions C of the second antiferromagnetic layer31and the two side portions C of the free magnetic layer28become weak. As a result, the magnetization directions of the two side portions C of the free magnetic layer28may not be sufficiently pinned in the track width direction.

Although the third antiferromagnetic layers33and the two side portions C of the second antiferromagnetic layer31function as a single antiferromagnetic layer due to the antiferromagnetic interaction via the nonmagnetic layer32, the third antiferromagnetic layer33and the second antiferromagnetic layer31are not physically a single layer. If the thickness of the second antiferromagnetic layer31is small, the second antiferromagnetic layer31only moderately transforms into an ordered structure. Thus, the exchange coupling magnetic field between the two side portions C of the second antiferromagnetic layer31and the two side portions C of the free magnetic layer28becomes weak. In view of the above, the thickness of the second antiferromagnetic layer31is set to at least 5 Å.

Moreover, shunt loss at the center portion D can be decreased and the read output can be increased by adjusting the thickness of the second antiferromagnetic layer31in the range of 5 to 50 Å.

The total of the thickness of the second antiferromagnetic layer31at the side portion C and the thickness of the third antiferromagnetic layer33is preferably in the range of 80 to 300 Å. In this manner, the two side portions C of the second antiferromagnetic layer31can properly exhibit antiferromagnetic characteristics and can be transformed in to an ordered structure by field annealing. As a result, exchange coupling magnetic fields are generated between the two side portions C of the second antiferromagnetic layer31and the two side portions C of the free magnetic layer28, and the magnetization directions of the two side portions C of the free magnetic layer28can be pinned in the track width direction.

The nonmagnetic layer32will now be explained. The nonmagnetic layer32functions as a protective layer for preventing the second antiferromagnetic layer31from being oxidized in air in a manufacturing method, as described below.

The nonmagnetic layer32is preferably composed of a material less easily oxidizable than Ta. Preferably, the nonmagnetic layer32is constituted from an element that does not affect the antiferromagnetic properties of the second antiferromagnetic layer31and the third antiferromagnetic layers33. This is because the element may diffuse into the second antiferromagnetic layer31and the third antiferromagnetic layers33during deposition or during field annealing for controlling the magnetization direction of the pinned magnetic layer23or free magnetic layer28.

In this embodiment, the nonmagnetic layer32is composed of Cr. Chromium is rarely oxidized in the thickness direction by exposure to air. Thus, the thickness of the nonmagnetic layer32is likely to be prevented from increasing due to oxidation resulting from exposure to air.

Moreover, when the nonmagnetic layer32is composed of Cr, the exchange coupling magnetic fields (Hex) between the second antiferromagnetic layer31and the free magnetic layer28at side portions can become larger than that with the nonmagnetic layer32composed of at least one of Ru, Re, Pd, Os, Ir, Pt, Au, and Rh.

When the second antiferromagnetic layer31composed of a PtMn alloy, the X—Mn alloy, or the Pt—Mn—X′ alloy is annealed along with the free magnetic layer28underneath and the third antiferromagnetic layers33on top, the PtMn alloy, the X—Mn alloy, or the Pt—Mn—X′ alloy transforms into an ordered structure. However, part around the interface between the second antiferromagnetic layer31and the free magnetic layer28does not easily transform into the ordered structure. When a nonmagnetic layer32composed of Cr is provided at the interface, the transformation into the ordered structure around the interface can progress nearly completely, thereby increasing the magnitudes of the exchange coupling magnetic fields generated at the interface.

When the nonmagnetic layer32composed of Cr is provided, chromium atoms of the nonmagnetic layer32diffuse into the second antiferromagnetic layer31. The diffused atoms promote transformation of the PtMn alloy, the X—Mn alloy, or the Pt—Mn—X′ alloy into ordered structures.

In this embodiment, because the nonmagnetic layer32, functioning as the protective layer, is disposed on the second antiferromagnetic layer31, the thickness h1of the second antiferromagnetic layer31can be reduced to a thickness in the range of 5 to 50 Å, for example, approximately 10 Å. When Cr atoms of the nonmagnetic layer32diffuse into the second antiferromagnetic layer31having such a small thickness, the transformation into ordered structures can be efficiently promoted around the interface between the second antiferromagnetic layer31and the free magnetic layer28, and the exchange coupling magnetic field generated at the interface can be increased.

Accordingly, in the magnetic sensing element of this embodiment, the magnetization of the two side portions C of the free magnetic layer28can be firmly pinned with the two side portions C of the second antiferromagnetic layer31. Thus, side reading can be reduced.

The crystal structure of the second antiferromagnetic layer31is, for example, of a CuAuI type. Chromium atoms diffusing from the nonmagnetic layer32partly replace the lattice points of the crystal lattice constituted from atoms of Pt and Mn, the crystal lattice constituted from atoms of X and Mn, or the crystal lattice constituted from atoms of Pt, Mn, and X′.

Whether chromium atoms of the nonmagnetic layer32are diffused into the second antiferromagnetic layer31and the third antiferromagnetic layers33can be examined by secondary ion mass spectrometry (SIMS) analysis, for example. When the second antiferromagnetic layer31is formed using a PtMn alloy and the nonmagnetic layer32is formed using Cr, a diffusion layer composed of a Cr—Pt—Mn alloy is formed by field annealing.

The thickness of the nonmagnetic layer32will now be explained. The nonmagnetic layer32is deposited to a thickness of 2 to 10 Å and preferably 2 to 5 Å. The nonmagnetic layer32composed of Cr is a dense layer that prevents oxidation in the thickness direction when exposed to air. Thus, the nonmagnetic layer32can adequately prevent the second antiferromagnetic layer31from being oxidized by exposure to air even at a small thickness.

The thickness of a center portion32bof the nonmagnetic layer32remains the same as initially deposited. This is because the center portion32bis not affected by ion milling, as will be described in later sections in the description of the fabrication process.

The two side portions32aof the nonmagnetic layer32are milled by ion milling. The thickness of the two side portions32ais smaller than the center portion32bof the nonmagnetic layer32. The reason for making the thickness of the center portion32blarger than that of the two side portions32ais to properly produce an antiferromagnetic interaction between the two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layers33so that the second antiferromagnetic layer31and the third antiferromagnetic layers33can function as a single antiferromagnetic layer. Note that the nonmagnetic layer32is provided between the second antiferromagnetic layer31and the third antiferromagnetic layers33. When the thickness of the nonmagnetic layer32is large, the concentration of Cr, which is a nonmagnetic substance, does not sufficiently decrease as a result of diffusion, and the nonmagnetic layer32remains thick after annealing. This eliminates the antiferromagnetic interaction between the second antiferromagnetic layer31and the third antiferromagnetic layers33. Since the second antiferromagnetic layer31alone is so thin that no exchange coupling magnetic field is generated between the second antiferromagnetic layer31alone and the free magnetic layer28, the magnetization of the two side portions C of the free magnetic layer28cannot be properly pinned.

As described above, the thickness of the two side portions32aof the nonmagnetic layer32is preferably 3 Å or less, and more preferably 1.0 Å or less. At such a small thickness, an antiferromagnetic interaction occurs between the two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layers33and the second antiferromagnetic layer31and the third antiferromagnetic layers33can thus function as a single antiferromagnetic layer.

The two side portions32aof the nonmagnetic layer32preferably have an average thickness of 0.2 Å or more. In this manner, the second antiferromagnetic layer31can remain unaffected by the ion milling and can thus exhibit sufficient magnetic characteristics.

As shown inFIG. 1, the two side portions32aof the nonmagnetic layer32can be milled to a small thickness of 3 Å or less because low-energy ion milling can be employed. The nonmagnetic layer32is formed as a thin layer, i.e., 2 to 10 Å, or more preferably, 2 to 5 Å, from the beginning. Thus, the thickness of the nonmagnetic layer32can be properly adjusted by employing low-energy ion milling. The milling rate is lower compared to that of high-energy ion milling, and it is relatively easy to stop milling before completely removing the nonmagnetic layer32.

Here, the term “low-energy ion milling” refers to ion milling employing ion beams having beam voltages (accelerating voltage) of less than 1,000 V. For example, beam voltages in the range of 100 to 500 V may be employed. In this embodiment, an Ar ion beam having a beam voltage of 200 V is used.

Preferably, a noble metal layer90is disposed between the nonmagnetic layer32and the second antiferromagnetic layer31, as indicated by a broken line in FIG.1.

When the nonmagnetic layer32is deposited directly on the second antiferromagnetic layer31, transformation into an ordered structure occurs even though the thickness of the second antiferromagnetic layer31is small. As a result, the exchange coupling magnetic field between the second antiferromagnetic layer31and the center portion of the free magnetic layer28readily increases, and the amount of change in the magnetization direction in response to external magnetic fields readily decreases. By providing the noble metal layer90between the nonmagnetic layer32and the second antiferromagnetic layer31, the tendency of the second antiferromagnetic layer31to transform into ordered structures can be adequately controlled. Accordingly, a decrease in the rate of change in magnetic resistance can be prevented.

The noble metal layer90is composed of at least one element selected from the group consisting of Ru, Re, Pd, Os, Ir, Pt, Au, and Rh.

In the embodiment shown inFIG. 1, the track width Tw is defined by the gap between the lower portions of the third antiferromagnetic layers33in the track width direction (the X direction in the drawing). The track width Tw is preferably 0.2 μm or less.

In the embodiment shown inFIG. 1, the magnetization directions of the two side portions C of the free magnetic layer28are properly pinned in the track width direction (the X direction). In contrast, the magnetization direction of the center portion D of the free magnetic layer28is only moderately put in a single-magnetic-domain state so that the magnetization direction can rotate in response to external magnetic fields. The length of the center portion D of the free magnetic layer28in the track width direction is approximately the same as the track width Tw. In this manner, the magnetization direction of part of the free magnetic layer28corresponding to the track width Tw can properly rotate in response to external magnetic fields.

In this embodiment, the second antiferromagnetic layer31is formed on the free magnetic layer28, and the nonmagnetic layer32is milled by ion milling. Thus, there is no danger of the free magnetic layer28being removed by ion milling, and magnetic characteristics of the free magnetic layer28are not degraded by damage inflicted by ion milling.

Moreover, since the second antiferromagnetic layer31is formed on the free magnetic layer28and the third antiferromagnetic layers33are formed on the two side portions C of the second antiferromagnetic layer31with the nonmagnetic layer32therebetween. According to this structure the magnetization of the free magnetic layer28can be properly controlled even with narrow tracks. Thus, a magnetic sensing element that meets the demand for narrower tracks can be obtained.

Second Embodiment

FIG. 2is a partial cross-sectional view of a magnetic sensing element according to a second embodiment of the present invention.

The magnetic sensing element inFIG. 2differs from the magnetic sensing element inFIG. 1in that the nonmagnetic layer32is provided only in the gap between the third antiferromagnetic layers33, i.e., the gap corresponding to the track width Tw. No nonmagnetic layer32is provided between the third antiferromagnetic layers33and the two side portions C of the second antiferromagnetic layer31.

As in the first embodiment shown inFIG. 1, the second antiferromagnetic layer31of this embodiment shown inFIG. 2has a thickness of 5 to 50 Å. The center portion D of the second antiferromagnetic layer31exhibits nonantiferromagnetic properties. The exchange coupling magnetic field between the center portion D of the second antiferromagnetic layer31and the center portion D of the free magnetic layer28is small if any. The magnetization direction of the center portion D of the free magnetic layer28is properly oriented in the track width direction (the X direction) and rotates in response to external magnetic fields.

The second antiferromagnetic layer31are disposed on the free magnetic layer28, and the third antiferromagnetic layer33is disposed directly on each of the two side portions C of the second antiferromagnetic layer31. The second antiferromagnetic layer31exhibits antiferromagnetic properties as a result of the antiferromagnetic interaction between the second antiferromagnetic layer31and the third antiferromagnetic layers33. When these layers are annealed in a magnetic field, the two side portions C of the second antiferromagnetic layer31transforms into an ordered structure, and exchange coupling magnetic fields are produced between the second antiferromagnetic layer31and the free magnetic layer28at the two side portions C. As a result, the magnetization direction of the free magnetic layer28in the two side portions C is firmly pinned in the track width direction (the X direction in the drawing).

The nonmagnetic layer32inFIG. 2is composed of Cr. When the nonmagnetic layer32is formed using Cr, oxidation rarely progresses in the layer thickness direction when exposed to air. The nonmagnetic layer32made of Cr can prevent the second antiferromagnetic layer31from being oxidized even when the nonmagnetic layer32has a small thickness. In this embodiment, the nonmagnetic layer32preferably has a thickness of 2 to 10 Å, and more preferably 2 to 5 Å immediately after the deposition.

As will be described in a manufacturing method below, the nonmagnetic layer32is initially formed over the entire surface of the second antiferromagnetic layer31, and two side portions of the nonmagnetic layer32is subsequently removed by ion milling to expose the second antiferromagnetic layer31at the two side portions C. The third antiferromagnetic layers33are then deposited on the second antiferromagnetic layer31at the two side portions C. Since the thickness of the nonmagnetic layer32is small, i.e., approximately 2 to 10 Å, the nonmagnetic layer32can be properly removed by low-energy ion milling. Controlling the milling process so as not to remove all of the second antiferromagnetic layer31is easier compared to when high-energy ion milling is employed. Thus, less damage is inflicted to the second antiferromagnetic layer31under the nonmagnetic layer32.

As described above, since the surface of the second antiferromagnetic layer31at the two side portions C suffers less from ion milling, the second antiferromagnetic layer31maintains superior magnetic characteristics.

In the magnetic sensing element shown inFIG. 2also, Cr atoms of the nonmagnetic layer32diffuse into the second antiferromagnetic layer31. Since the nonmagnetic layer32, functioning as a protective layer, is provided on the second antiferromagnetic layer31, the thickness h1of the second antiferromagnetic layer31can be reduced to 5 to 50 Å, for example, to approximately 10 Å. Chromium atoms diffusing into the second antiferromagnetic layer31from the nonmagnetic layer32promote transformation into an ordered structure around the interface between the second antiferromagnetic layer31and the free magnetic layer28. This increases the magnitude of the exchange coupling magnetic field generated at the interface.

Accordingly, the magnetization directions of the free magnetic layer28at the two side portions C can be firmly pinned by the two side portions C of the second antiferromagnetic layer31. Side reading can be reduced.

The crystal structure of the second antiferromagnetic layer31is, for example, of a CuAuI type. Chromium atoms diffusing from the nonmagnetic layer32partly replace the lattice points of the crystal lattice constituted from atoms of Pt and Mn, the crystal lattice constituted from atoms of X and Mn, or the crystal lattice constituted from atoms of Pt, Mn, and X′.

In the embodiment shown inFIG. 2, the second antiferromagnetic layer31is disposed on the free magnetic layer28, and the nonmagnetic layer32is milled by ion milling. Unlike conventional techniques, ion milling does not affect the free magnetic layer28. The problem of magnetic characteristics degradation of the free magnetic layer28due to damage inflicted by ion milling does not occur.

According to the structure shown inFIG. 2, the magnetization directions of the free magnetic layer28can be properly controlled even with narrower tracks, and a magnetic sensing element that can meet the demand for narrower tracks can be obtained.

Note that the second antiferromagnetic layer31at the two side portions C may be partially milled, as shown by a broken line E in FIG.2. In such a case, the thickness of the second antiferromagnetic layer31at the two side portions C becomes smaller than the thickness at the center portion D. However, since the second antiferromagnetic layer31at the two side portions C is removed by low-energy ion milling, the damage inflicted to the two side portions C is less compared to when high-energy ion milling is employed. The second antiferromagnetic layer31at the two side portions C shows antiferromagnetic characteristics and generates exchange coupling magnetic fields sufficient for firmly pinning the magnetization direction of the free magnetic layer28at the two side portions C.

Third Embodiment

FIG. 3is a partial cross-sectional view of a magnetic sensing element according to a third embodiment of the present invention viewed from the opposing face.

The embodiment shown inFIG. 3differs from that shown inFIG. 1in that the nonmagnetic layer32has a uniform thickness. In other words, the center portion32band the two side portions32aof the nonmagnetic layer32have the same thickness.

When the thickness of the nonmagnetic layer32exceeds 3 Å, the concentration of Cr, which is the nonmagnetic substance, does not sufficiently decrease as a result of diffusion, and the nonmagnetic layer32remains thick after annealing. This eliminates the antiferromagnetic interaction between the second antiferromagnetic layer31and the third antiferromagnetic layers33and inhibits the second antiferromagnetic layer31at the two side portions C and the third antiferromagnetic layers33from functioning as a single antiferromagnetic layer. Since the second antiferromagnetic layer31alone is so thin that no exchange coupling magnetic field is generated between the second antiferromagnetic layer31alone and the free magnetic layer28, the two side portions C of the second antiferromagnetic layer31do not properly transform into an ordered structure by field annealing. As a result, the exchange coupling magnetic fields generated between the two side portions C of the second antiferromagnetic layer31and the free magnetic layer28becomes small, if any. Moreover, the magnetization of the two side portions C of the free magnetic layer28cannot be firmly pinned in the track width direction (the X direction).

Accordingly, in this embodiment, the thickness of the nonmagnetic layer32should be 3 Å or less. More preferably, the thickness of the nonmagnetic layer32is 1 Å or less. The nonmagnetic layer32may have an average thickness of 0.2 Å. In other words, the average thickness of the nonmagnetic layer32is preferably in the range of 0.2 to 3 Å, and more preferably in the range of 0.2 to 1 Å.

As in the first embodiment, the second antiferromagnetic layer31of the third embodiment shown inFIG. 3preferably has a thickness of 5 to 50 Å. The center portion D of the second antiferromagnetic layer31exhibits nonantiferromagnetic or nonmagnetic properties. The exchange coupling magnetic field between the center portion D of the second antiferromagnetic layer31and the center portion D of the free magnetic layer28is small, if any. The magnetization direction of the center portion D of the free magnetic layer28is properly oriented in the track width direction (the X direction) and rotates in response to external magnetic fields.

The second antiferromagnetic layer31are disposed on the free magnetic layer28, and the third antiferromagnetic layer33is disposed on each of the two side portions C of the second antiferromagnetic layer31with the nonmagnetic layer32therebetween. The second antiferromagnetic layer31exhibits antiferromagnetic properties as a result of the antiferromagnetic interaction between the second antiferromagnetic layer31and the third antiferromagnetic layers33. When these layers are annealed in a magnetic field, the two side portions C of the second antiferromagnetic layer31transforms into an ordered structure, and exchange coupling magnetic fields are produced between the second antiferromagnetic layer31and the free magnetic layer28at the two side portions C. As a result, the magnetization direction of the free magnetic layer28in the two side portions C is firmly pinned in the track width direction (the X direction in the drawing).

Unlike conventional techniques, in this embodiment shown inFIG. 3, the free magnetic layer28is unaffected by ion milling, and the problem of magnetic characteristics degradation of the free magnetic layer28due to damage inflicted by ion milling does not occur.

According to the structure shown inFIG. 3, the magnetization directions of the free magnetic layer28can be properly controlled even with narrower tracks, and a magnetic sensing element that can meet the demand for narrower tracks can be obtained.

In the magnetic sensing element shown inFIG. 3also, chromium atoms of the nonmagnetic layer32diffuse into the second antiferromagnetic layer31. The diffusion of Cr atoms into the second antiferromagnetic layer31promotes the transformation of the PtMn alloy, the X—Mn alloy, and the Pt—Mn—X′ alloy into an ordered structure.

Accordingly, in the magnetic sensing element of this embodiment, the magnetization direction of the free magnetic layer28at the two side portions C can be firmly pinned in relation with the two side portions C of the second antiferromagnetic layer31, and side reading can be prevented.

In this embodiment, the crystal structure of the second antiferromagnetic layer31is, for example, of a CuAuI type. Chromium atoms diffusing from the nonmagnetic layer32partly replace the lattice points of the crystal lattice constituted from atoms of Pt and Mn, the crystal lattice constituted from atoms of X and Mn, or the crystal lattice constituted from atoms of Pt, Mn, and X′.

Fourth Embodiment

FIG. 4is a partial cross-sectional view of a magnetic sensing element according to a fourth embodiment of the present invention.

Referring toFIG. 4, the seed layer21, the first antiferromagnetic layer22, the pinned magnetic layer23, the nonmagnetic material layer27, the free magnetic layer28, the second antiferromagnetic layer31, and the third antiferromagnetic layers33are sequentially formed on the substrate20. The material of each layer is the same as that of the first embodiment described above.

In this embodiment shown inFIG. 4, the third antiferromagnetic layer33is formed on each of the two side portions32aof the nonmagnetic layer32. The electrode layer34is disposed on each of the third antiferromagnetic layers33with an interlayer35therebetween. The interlayer35is composed of Ta or the like.

In the embodiment shown inFIG. 4, the track width Tw is determined by the gap between the lower faces of the third antiferromagnetic layers33. The track width Tw is preferably 0.2 μm or less.

The nonmagnetic layer32covers the entire surface of the second antiferromagnetic layer31. The nonmagnetic layer32is thin and is composed of Cr. The Cr layer is rarely oxidized in the thickness direction when exposed to air.

The thickness of the nonmagnetic layer32is preferably 0.2 to 3 Å, and more preferably 0.2 to 1.0 Å. The term “thickness of 0.2 Å ” means the average thickness of the entire nonmagnetic layer32is 0.2 Å. Since the size of atoms is larger than 0.2 Å, the nonmagnetic layer32having an average thickness of 0.2 Å has an island structure including regions without atoms and regions with atoms.

When the nonmagnetic layer32has such a small thickness, an antiferromagnetic interaction can still be produced between the second antiferromagnetic layer31and the third antiferromagnetic layer33, although the nonmagnetic layer32is provided therebetween. As a result, the second antiferromagnetic layer31at the two side portions C exhibits antiferromagnetic properties and transforms into an ordered structure by field annealing. Exchange coupling magnetic fields are then produced between the second antiferromagnetic layer31and the free magnetic layer28at the two side portions C, and the magnetization of the two side portions C of the free magnetic layer28is firmly pinned in the track width direction (the X direction).

Although the second antiferromagnetic layer31is formed on the center portion D of the free magnetic layer28, the thickness of the second antiferromagnetic layer31is so small that the second antiferromagnetic layer31alone does not exhibit antiferromagnetic properties. The thickness of the second antiferromagnetic layer31is preferably 5 to 50 Å, more preferably 10 to 50 Å, and most preferably 30 to 40 Å.

With this structure, the center portion D of the second antiferromagnetic layer31rarely transforms into an ordered structure even when field annealed. The exchange coupling magnetic field between the free magnetic layer28and the second antiferromagnetic layer31at the center portion D is small, if any. The magnetization direction of the free magnetic layer28at the center portion D is moderately put in a single-magnetic-domain state so that the magnetization direction can rotate in response to external magnetic fields.

When the nonmagnetic layer32is composed of Cr, the exchange coupling magnetic fields (Hex) between the second antiferromagnetic layer31and the free magnetic layer28can become larger than that with the nonmagnetic layer32composed of at least one of Ru, Re, Pd, Os, Ir, Pt, Au, and Rh.

The material, i.e., chromium, of the nonmagnetic layer32may diffuse into the second antiferromagnetic layer31and third antiferromagnetic layers33during field annealing for controlling the magnetization directions of the resist layer38and the pinned magnetic layer23. In particular, when the second antiferromagnetic layer31and the third antiferromagnetic layers33are composed of a PtMn alloy and the nonmagnetic layer32is composed of Cr, the region around the upper face of the second antiferromagnetic layer31and the region around the lower face of each third antiferromagnetic layer33become an antiferromagnetic layer composed of Cr—Pt—Mn.

In this embodiment, the nonmagnetic layer32functioning as a protective layer is deposited on the second antiferromagnetic layer31. Thus, the thickness h1of the second antiferromagnetic layer31can be reduced to a thickness of 5 to 50 Å, e.g., approximately 10 Å. Chromium atoms diffusing from the nonmagnetic layer32into the second antiferromagnetic layer31having such a small thickness effectively promote the transformation into an ordered structure around the interface between the second antiferromagnetic layer31and the free magnetic layer28. Thus, the magnitude of the exchange coupling magnetic field generated at the interface can be increased.

Accordingly, in the magnetic sensing element of this embodiment, the magnetization of the two side portions C of the free magnetic layer28can be firmly pinned with the two side portions C of the second antiferromagnetic layer31. Thus, side reading can be reduced.

The fourth embodiment shown inFIG. 4differs from the first to third embodiment shown inFIGS. 1to3in that the end33aof each third antiferromagnetic layer33is perpendicular to the surface of the substrate20, i.e., extends along the Z direction in the drawing. Such a difference in shape is derived from the difference in the manufacturing processes, as will be described later.

Alternatively, as in the first to third embodiments shown inFIGS. 1to3, the side end face33amay be formed as a flat or curved slope in such a manner that the gap between the ends33aof the third antiferromagnetic layers33gradually increases along the Z direction.

The magnetic sensing elements shown inFIGS. 1to3are manufactured by the same process whereas the magnetic sensing elements shown inFIGS. 4to6(the fourth to six embodiments) are manufactured by a different process. The magnetic sensing elements shown inFIGS. 1to3are similar in that the center portion32bof the nonmagnetic layer32is disposed in the gap between the third antiferromagnetic layers33. In contrast, the magnetic sensing elements shown inFIGS. 4to6are similar in that the nonmagnetic layer32is provided between the third antiferromagnetic layers33and the two side portions C of the second antiferromagnetic layer31.

The structures of magnetic sensing elements according to other embodiments manufactured by the same process as that of the fourth embodiment will now be described.

Fifth Embodiment

FIG. 5is a partial cross-sectional view of a magnetic sensing element according to a fifth embodiment of the present invention viewed from the opposing face.

The magnetic sensing element of fifth embodiment differs from that of the fourth embodiment in that the third antiferromagnetic layer33is disposed on the center portion32bof the nonmagnetic layer32.

In this embodiment shown inFIG. 5, the two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layers33are separated from each other by the nonmagnetic layer32having a thickness of 0.2 to 3 Å therebetween and function as a single antiferromagnetic layer as a result of an antiferromagnetic interaction. The two side portions C of the second antiferromagnetic layer31exhibit antiferromagnetic properties. When field-annealed, the two side portions C of the second antiferromagnetic layer31transform into an ordered structure, and exchange coupling magnetic fields are generated between the second antiferromagnetic layer31and the free magnetic layer28at the two side portions C. The two side portions C of the free magnetic layer28is thereby firmly pinned in the track width direction (the X direction).

The thickness of the third antiferromagnetic layer33is smaller in the center portion D than in the two side portions C.

Thus, the sum of the thickness h2of the second antiferromagnetic layer31the thickness h3of the third antiferromagnetic layer33at the center portion D must be small. Otherwise, the second antiferromagnetic layer31exhibits antiferromagnetic properties by an antiferromagnetic interaction with then third antiferromagnetic layer33, and ah exchange coupling magnetic field is generated between the second antiferromagnetic layer31and the free magnetic layer28at the center portion D, which is undesirable.

Thus, the sum of the thickness h2and the thickness h3is preferably in the range of 5 to 50 Å, more preferably 10 to 50 Å, and most preferably 30 to 40 Å.

At such a thickness, the center portion D of the second antiferromagnetic layer31rarely transforms into an ordered structure by field annealing, and the antiferromagnetic interaction rarely occurs between the second antiferromagnetic layer31and the third antiferromagnetic layer33. Thus, the second antiferromagnetic layer31does not exhibit antiferromagnetic properties. The exchange coupling magnetic field generated between the second antiferromagnetic layer31and the free magnetic layer28at the center portion D is small, if any. The magnetization direction in the center portion D of the free magnetic layer28is prevented from being pinned as firmly as the magnetization directions in the two side portions C.

In the embodiment shown inFIG. 5, the center portion D of the free magnetic layer28is moderately put in a single-magnetic-domain state so that the magnetization direction can rotate in response to external magnetic fields. This magnetic sensing element has superior sensitivity that can meet the demand for narrow tracks.

When the nonmagnetic layer32is composed of Cr, the exchange coupling magnetic fields (Hex) between the second antiferromagnetic layer31and the free magnetic layer28become larger than that with the nonmagnetic layer32composed of at least one of Ru, Re, Pd, Os, Ir, Pt, Au, and Rh.

Accordingly, in the magnetic sensing element of this embodiment, the magnetization of the two side portions C of the free magnetic layer28can be firmly pinned with the two side portions C of the second antiferromagnetic layer31. Thus, side reading can be reduced.

Preferably, the noble metal layer90is disposed between the nonmagnetic layer32and the second antiferromagnetic layer31.

When the nonmagnetic layer32is deposited directly on the second antiferromagnetic layer31, transformation of the second antiferromagnetic layer31into an ordered structure occurs even though the thickness of the second antiferromagnetic layer31is small. As a result, the exchange coupling magnetic field between the second antiferromagnetic layer31and the free magnetic layer28at the center portion readily increases, and the amount of change in the magnetization direction in response to external magnetic fields readily decreases. By providing the noble metal layer90between the nonmagnetic layer32and the second antiferromagnetic layer31, the tendency of the second antiferromagnetic layer31toward transformation into ordered structures can be adequately controlled. Accordingly, a decrease in the rate of change in magnetic resistance can be prevented.

The noble metal layer90is composed of at least one element selected from the group consisting of Ru, Re, Pd, Os, Ir, Pt, Au, and Rh.

Sixth Embodiment

FIG. 6is a partial cross-sectional view of a magnetic sensing element according to a sixth embodiment of the present invention viewed from the opposing face.

The magnetic sensing element shown inFIG. 6differs from that shown inFIG. 4in that no nonmagnetic layer32is provided in the gap between the third antiferromagnetic layers33and that part of the second antiferromagnetic layer31is removed.

In the embodiment shown inFIG. 6, the nonmagnetic layer32composed of Cr having a thickness of 0.2 to 3 Å is formed on the third antiferromagnetic layer33at each of the two side portions C, and the third antiferromagnetic layer33is formed on each nonmagnetic layer32. The sum of the thickness of the third antiferromagnetic layer33and the second antiferromagnetic layer31at each of the two side portions C is preferably large, namely, 80 to 300 Å.

According to this structure, an antiferromagnetic interaction occurs between the two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layers33through the nonmagnetic layers32. The two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layer33functions as a single antiferromagnetic layer, and the two side portions C of the second antiferromagnetic layer31thus exhibit antiferromagnetic properties. The two side portions C of the second antiferromagnetic layer31transform into an ordered structure by field annealing, and exchange coupling magnetic fields are generated between the second antiferromagnetic layer31and the free magnetic layer28at the two side portions C. As a result, the two side portions C of the free magnetic layer28is firmly pinned in the track width direction (the X direction).

The thickness of the second antiferromagnetic layer31at the center portion D is small, namely, 5 to 50 Å. At such a small thickness, the center portion D of the second antiferromagnetic layer31does not exhibit antiferromagnetic properties and does not transform into an ordered structure by field annealing. The exchange coupling magnetic field between the second antiferromagnetic layer31and the free magnetic layer28at the center portion D is small, if any. Accordingly, the center portion D of the free magnetic layer28is moderately put to a single-magnetic-domain state so that the magnetization direction of the center portion D can rotate in response to external magnetic fields. Thus, a magnetic sensing element having superior sensitivity that can meet the demand for narrower tracks can be obtained.

Alternatively, the center portion D of the second antiferromagnetic layer31may be completely removed, as indicated by broken lines F inFIG. 6so as to expose the center portion D of the free magnetic layer28. In this manner, however, the exposed center portion D of the free magnetic layer28is likely to suffer damage inflicted by ion milling or reactive ion etching (RIE). It is preferable to leave some of the second antiferromagnetic layer31on the center portion D of the free magnetic layer28.

In the embodiment shown inFIG. 6, the center portion D of the second antiferromagnetic layer31is removed by ion milling. Damage inflicted by ion milling on the center portion D of the second antiferromagnetic layer31may degrade the magnetic characteristics. However, the center portion D of the second antiferromagnetic layer31is sufficiently thin so as not to exhibit antiferromagnetic properties and thus does not magnetically influence layers such as free magnetic layer28. Damage on the center portion D of the second antiferromagnetic layer31by ion milling is not likely to significantly affect the read characteristics.

When the nonmagnetic layer32is composed of Cr, the exchange coupling magnetic fields (Hex) between the second antiferromagnetic layer31and the free magnetic layer28at side portions C can become larger than that with the nonmagnetic layer32composed of at least one of Ru, Re, Pd, Os, Ir, Pt, Au, and Rh.

Accordingly, in the magnetic sensing element of this embodiment, the magnetization of the two side portions C of the free magnetic layer28can be firmly pinned with the two side portions C of the second antiferromagnetic layer31. Thus, side reading can be reduced.

In the above-described fourth to sixth embodiments shown inFIGS. 4to6, instead of providing a separate nonmagnetic layer32, chromium atoms may be diffused into the second antiferromagnetic layer31. In such a case, the concentration of Cr atoms preferably increases toward the upper face of the second antiferromagnetic layer31.

In the magnetic sensing elements according to the first to sixth embodiments shown inFIGS. 1to6, the electrode layer34is disposed on the third antiferromagnetic layer33disposed on each of two sides of the composite comprising layers from the substrate20to the second antiferromagnetic layer31. According to this structure, an electric current flows in the composite in a direction parallel to the surfaces of layers constituting the composite (a current-in-the-plane (CIP) magnetic sensing element).

Seventh Embodiment

FIG. 7is a partial cross-sectional view of a magnetic sensing element according to a seventh embodiment of the present invention.

As shown inFIG. 7, the magnetic sensing element has a lower shield layer65and an upper shield layer68at the bottom and the top, respectively, of the composite film that includes layers from the seed layer21to the second antiferromagnetic layer31. The shield layers65and68also function as electrode layers. An electric current flows in the composite film between the shield layers65and68in a direction perpendicular to the surfaces of the layers of the composite film (current-perpendicular-to-the-plane (CPP) magnetic sensing element). The present invention is applicable to CPP magnetic sensing elements.

The layer structure of the composite film is the same as that of the first embodiment. The description is omitted to avoid redundancy. Note that the seed layer21shown inFIG. 7may be omitted.

As shown inFIG. 7, the lower shield layer65that functions as the lower electrode is disposed under the seed layer21. The lower shield layer65is made by plating a magnetic material such as permalloy (NiFe).

The third antiferromagnetic layer33is formed on each of the two side portions C of the composite film with the nonmagnetic layer32therebetween. An insulating layer67is formed over the upper face33band the end33a.

Referring again toFIG. 7, the upper shield layer68that also functions as the upper electrode is disposed over the insulating layer67and the center portion32bof the nonmagnetic layer32.

According to this structure the electric current flows in the composite film in a direction parallel to the surfaces of the layers of the composite film.

Since the upper faces33band the ends33aof the third antiferromagnetic layer33are covered with the insulating layers67, the electric current flowing from the upper shield layer68into the composite film does not shunt to the third antiferromagnetic layers33. Thus, the structure shown inFIG. 7prevents the current path from deviating outside the track width Tw. A CPP magnetic sensing element having a large output can be obtained.

Ends67aof the insulating layers67preferably cover the two sides of the center portion32bof the nonmagnetic layer32, as indicated by a dotted chain line in FIG.7. According to this structure, the electric current can be prevented from shunting into the third antiferromagnetic layers33.

A nonmagnetic layer69indicated by a broken line inFIG. 7may be provided over the insulating layer67and the center portion32bof the nonmagnetic layer32, if necessary. The nonmagnetic layer69is preferably composed of a nonmagnetic conductive material such as Ta, Ru, Rh, Ir, Cr, Re, or Cu. The nonmagnetic layer69functions as an upper gap layer. Since the nonmagnetic layer69is disposed on the surface of the center portion D of the composite film, which is the entrance and exit of the electric current, an insulating material that inhibits the current from flowing into the sensing element is not preferred. The nonmagnetic layer69is preferably made of a nonmagnetic conductive material.

In this embodiment, the nonmagnetic material layer27shown inFIG. 7may be made of a nonmagnetic conductive material so as to make a CPP spin-valve GMR head. Alternatively, the nonmagnetic material layer27may be made of an insulating material such as Al2O3or SiO2so as to make a CPP spin-valve tunneling magnetoresistive (TMR) head.

A tunneling magnetoresistive element utilized a spin tunneling effect to generate changes in resistance. When the magnetization directions of the pinned magnetic layer23and the free magnetic layer28are antiparallel to each other, tunneling current is prevented from flowing through the nonmagnetic material layer27, thereby giving the maximum resistance. When the magnetization directions of the pinned magnetic layer23and the free magnetic layer28are parallel to each other, the tunneling current flows easily, thereby giving the minimum resistance.

Based on this principle, as the magnetization direction of the free magnetic layer28changes in response to an external magnetic field, a change in electrical resistance is detected as a change in voltage (constant current operation) or as a change in current (constant voltage operation) so as to detect the leakage magnetic field from a recording medium.

Eighth and Ninth Embodiments

FIG. 8shows a magnetic sensing element according to an eighth embodiment of the present invention. The magnetic sensing element is of a CPP type combining the magnetic sensing element shown in FIG.2and the magnetic sensing element shown in FIG.7.FIG. 9shows a magnetic sensing element according to a ninth embodiment of the present invention. The magnetic sensing element of this embodiment is of a CPP type combining the magnetic sensing element shown in FIG.3and the magnetic sensing element shown in FIG.7.

Tenth Embodiment

FIG. 10shows a magnetic sensing element according to a tenth embodiment of the present invention. The magnetic sensing element is of a CPP type combining the magnetic sensing element shown in FIG.4and the magnetic sensing element shown in FIG.7. The magnetic sensing element shown inFIG. 10differs from that shown inFIG. 7in that first insulating layer70is formed on each upper face33bof the third antiferromagnetic layer33and that a separate second insulating layer71is formed on each end33aof the third antiferromagnetic layer33. These differences are derived from differences in fabrication methods.

The first insulating layer70and the second insulating layer71have the same function as that of the insulating layer67shown in FIG.7. The first and second insulating layers70and71properly prevents an electric current flowing in the composite film from shunting into the third antiferromagnetic layers33from the upper shield layer68.

The first and second insulating layers70and71are composed of an insulating material such as Al2O3, SiO2, AlN, Al—Si—O—N, Al—Si—O, Ti2O3, Ti3O5, or Ta2O5.

In the embodiment shown inFIG. 10, the end33aof the third antiferromagnetic layer33is perpendicular with respect to the track width direction (the X direction). Alternatively, the gap between the third antiferromagnetic layers33may be arranged to gradually increase along the Z direction. In such a case each end33amay be formed as a flat or curved slope.

When the ends33aare formed as flat or curved slopes, it is relatively easy to deposit the second insulating layers71to a proper thickness on the ends33a. Thus, shunt loss can be decreased.

As shown inFIG. 10, the upper face33band the ends33aof the third antiferromagnetic layer33are covered with the first and second insulating layers70and71. According to this structure, an electric current flowing in the composite film does not shunt into the third antiferromagnetic layers33and flows within the track width Tw determined by the gap between the second insulating layers71. The magnetic sensing element shown inFIG. 10can thus exhibit large output.

The nonmagnetic layer69may be provided over the first and second insulating layers70and71and the center portion D of the composite film, as indicated by a broken line in FIG.10. The nonmagnetic layer69is preferably composed of a nonmagnetic conductive material such as Ta, Ru, Rh, Ir, Cr, Re, or Cu. The nonmagnetic layer69functions as an upper gap layer. Since the nonmagnetic layer69is disposed on the surface of the center portion D of the composite film, which is the entrance and exit of the electric current, an insulating material that inhibits the current from flowing into the sensing element is not preferred. The nonmagnetic layer69is preferably made of a nonmagnetic conductive material.

In this embodiment shown inFIG. 10, the nonmagnetic material layer27may be made of a nonmagnetic conductive material so as to make a CPP spin-valve GMR head. Alternatively, the nonmagnetic material layer27may be made of an insulating material such as Al2O3or SiO2so as to make a CPP spin-valve tunneling magnetoresistive (TMR) head.

Eleventh and Twelfth Embodiments

FIG. 11shows a CPP magnetic sensing element according to a eleventh embodiment of the present invention combining the magnetic sensing element shown in FIG.5and the magnetic sensing element shown in FIG.10.FIG. 12shows a CPP magnetic sensing element according to a twelfth embodiment of the present invention combining the magnetic sensing element shown in FIG.6and the magnetic sensing element shown in FIG.10.

Thirteenth and Fourteenth Embodiments

Magnetic sensing elements according to the thirteenth and fourteenth embodiments of the present invention shown inFIGS. 13 and 14are the same as those shown inFIGS. 7 and 12in that they are of a CPP type but differ in the shape of the lower shield layer65.

Referring now toFIG. 13, the lower shield layer65, which also functions as the lower electrode, of the magnetic sensing element according of the thirteenth embodiment has a protrusion65aat the center portion D in the track width direction (the X direction). The protrusion65aprojects toward the composite film in the Z direction. An upper face65a1of the protrusion65ais in contact with the lower face of the seed layer21. In this structure, an electric current flows into the composite film via the protrusion65a(or an electric current flows from the composite film to the protrusion65a).

In the thirteenth embodiment shown inFIG. 13, an insulating layer78is formed on each of two side portions65bof the lower shield layer65in the track width direction and between the side portion65band the seed layer21. The insulating layer78is composed of an insulating material such as Al2O3, SiO2, AlN, Al—Si—O—N, Al—Si—O, Ti2O3, Ti3O5, or Ta2O5.

In the embodiment shown inFIG. 13, the current path is narrowed by the protrusion65aof the lower shield layer65. Since the insulating layers78are provided between the composite film and the two side portions65bof the lower shield layer65, the electric current flowing in the composite film is prevented from shunting through the two side portions65b. As a result, the magnetic sensing element exhibits large output with narrower effective track width.

In the embodiment shown inFIG. 13, the length of the upper face65a1of the protrusion65aof the lower shield layer65in the track width direction (the X direction) is the same as that of the center portion D in the track width direction (the X direction). Alternatively, the length of the upper face65a1in the track width direction may be larger than that of the center portion D. Most preferably, the length of the upper face65a1in the track width direction is the same as that of the track width Tw. In this manner, an electric current can be effectively supplied to the magnetic sensing element only in the side portion. Thus, the magnetic sensing element exhibits a large output.

As shown inFIG. 13, two side faces65a2of the protrusion65aare formed as flat or curved slopes so that the length of the protrusion65ain the track width direction gradually increases along the direction opposite to the Z direction. Alternatively, the two side faces65a2may be perpendicular to the track width direction (the X direction).

The magnetic sensing element of the fourteenth embodiment shown inFIG. 14also has the lower shield layer65having the same shape as in the thirteenth embodiment shown in FIG.13. Since the arrangement of the upper face65a1, the seed layer21, and the insulating layers78are the same as in the thirteenth embodiment, the description thereof is omitted to avoid redundancy.

The fourteenth embodiment differs from the thirteenth embodiment in that no insulating layer67is provided on the upper face33band the ends33aof the third antiferromagnetic layer33. Moreover, the upper shield layer68, which also functions as the upper electrode, is in direct contact with the center portion D of the composite film and the third antiferromagnetic layers33.

In the embodiment shown inFIG. 14, the upper shield layer68is not insulated from the third antiferromagnetic layers33. Thus, the current path tends to broaden beyond the track width Tw, and the output may be degraded as a result. However, since the protrusion65aof the lower shield layer65narrows the current path at the bottom face of the magnetic sensing element, the broadening of the current path can be inhibited, and a decrease in output can be avoided.

Preferably, the upper face65a1of the protrusion65aformed in the lower shield layer65is flush with the upper faces of the insulating layers78disposed at the sides. In this manner, layers of the composite film can be formed parallel to each other in the track width direction, and a magnetic sensing element having superior read characteristics can be made.

Note that the thirteenth and fourteenth embodiments shown inFIGS. 13 and 14may be applied to a CPP magnetic sensing element shown inFIGS. 8to12.

The CPP magnetic sensing elements shown inFIGS. 7to14have the lower and upper shield layers (electrodes)65and68in contact with the bottom and the top of the composite film, respectively, so that no separate electrode layers are necessary. Thus, the process for making CPP magnetic sensing elements can be simplified.

Moreover, when the shield layers also function as electrodes, the gap length G1between shield layers can be decreased (refer to FIG.7). Note when the nonmagnetic layer69is provided, the gap length G1also determined by the thickness of the nonmagnetic layer69. Accordingly, a magnetic sensing element that can meet the trend for higher recording density can be obtained.

The application of the present invention is not limited to the embodiments shown inFIGS. 7to14. An electrode layer composed of Au, W, Cr, Ta, or the like may be provided at the bottom and/or the top of the composite film, and a shield layer composed of magnetic material may be disposed on the surface of the electrode layer remote from the magnetic sensing element.

The free magnetic layer28of the present invention will now be described.

The free magnetic layer28shown in each of the first to fourteenth embodiments shown inFIGS. 1to14has a two-layer structure comprising the anti-diffusion sublayer29and the magnetic material sublayer30. The anti-diffusion sublayer29is composed of Co, CoFe, or the like and prevents interdiffusion between the free magnetic layer28and the nonmagnetic material layer27. The magnetic material sublayer30is disposed on the anti-diffusion sublayer29and is composed of a magnetic material such as a NiFe alloy.

Alternatively, the free magnetic layer28may be of a single layer structure composed of a magnetic material such as a NiFe alloy, a CoFe alloy, a CoFeNi alloy, elemental Co, or a CoNi alloy. Preferably, the free magnetic layer is composed of a CoFeNi alloy.

FIG. 15is an enlarged partial cross-sectional view of an example of the free magnetic layer28according to the present invention viewed from the opposing face.

InFIG. 15, the free magnetic layer28has a three-layer structure comprising a magnetic material sublayers36to38. The magnetic material sublayer36is an anti-diffusion sublayer for preventing the diffusion of atoms into the nonmagnetic material layer27. The magnetic material sublayer36is composed of CoFe, Co, or the like.

The magnetic material sublayer38is in contact with the second antiferromagnetic layer31. The magnetic material sublayer38is preferably made of a CoFe alloy so that the magnitude of the exchange coupling magnetic field generated between the magnetic material sublayer38and the second antiferromagnetic layer31can be increased.

An example of the materials for the three-layer structure is magnetic material sublayer36: CoFe/magnetic material sublayer37: NiFe/magnetic material sublayer38: CoFe.

The thickness of the free magnetic layer28composed of only a magnetic material is preferably approximately 30 to 40 Å. An example of the composition of a CoFe alloy used in the free magnetic layer28is Co: 90 at % and Fe: 10 at %.

FIG. 16is an enlarged partial cross sectional view of another example of the free magnetic layer28. The free magnetic layer28shown inFIG. 16has a so-called synthetic ferrimagnetic structure. With this structure, the effective magnetic thickness of the free magnetic layer28can be decreased without significantly decreasing the physical thickness of the free magnetic layer28. Thus, the sensitivity toward external magnetic fields can be enhanced.

Referring toFIG. 16, the free magnetic layer28is constituted from magnetic sublayers39and41and a nonmagnetic interlayer40. The magnetic sublayers39and41are composed of a magnetic material such as a NiFe alloy, a CoFe alloy, a CoFeNi alloy, elemental Co, or a CoNi alloy. Preferably, at least one of the magnetic sublayers39and41is composed of a CoFeNi alloy. The CoFeNi alloy preferably contains 9 to 17 at % of Fe, 0.5 to 10 at % of Ni, and the balance being Co.

In this manner, the coupling magnetic field resulting from a Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction can be increased. In particular, the spin-flop magnetic field (Hsf) can be increased to approximately at least 293 kA/m. As a result, the magnetization directions of the magnetic sublayers39and41can be properly oriented antiparallel to each other. Moreover, by using the CoFeNi alloy satisfying the above-described composition ranges, the magnetostriction of the free magnetic layer28can be adjusted within the range of −3×10−6to 3×10−6, and the coercive force can be reduced to 790 A/m or less. Moreover, the soft magnetic characteristics of the free magnetic layer28can be improved, and a decrease in amount of change in resistance (ΔR) and in rate of change in resistance (ΔR/R) due to diffusion of Ni atoms between the free magnetic layer28and the nonmagnetic material layer27can be avoided.

The nonmagnetic interlayer40is preferably made of at least one selected from the group consisting of Ru, Rh, Ir, Cr, Re, and Cu.

The thickness of the magnetic sublayer39is, for example, approximately 35 Å. The thickness of the nonmagnetic interlayer40is, for example, approximately 9 Å. The thickness of the magnetic sublayer41is, for example, approximately 15 Å.

Fifteenth Embodiment

A magnetic sensing element having the free magnetic layer28of a synthetic ferromagnetic structure is illustrated inFIG. 19(a fifteenth embodiment). As shown inFIG. 19, the layers from the magnetic sublayer41and above are completely removed at the center portion D, and the nonmagnetic interlayer40is exposed between the third antiferromagnetic layers33. According to this structure, the center portion D of the free magnetic layer28does not have a synthetic ferrimagnetic structure and functions as a free magnetic layer composed of only a normal magnetic layer. In contrast, the two side portions C of the free magnetic layer28have a synthetic ferrimagnetic structure. This structure increases the magnitude of the unidirectional bias magnetic field, reliably pins the magnetization directions of the two side portions C of the free magnetic layer28in the track width direction, and prevents side reading.

An anti-diffusion layer composed of a CoFe alloy, elemental Co, or the like may be formed between the magnetic sublayer and the nonmagnetic material layer27. Moreover, a magnetic layer made of a CoFe alloy may be provided between the magnetic sublayer41and the second antiferromagnetic layer31.

In such a case, the CoFeNi alloy constituting the magnetic sublayer and/or the magnetic sublayer41preferably contains 7 to 15 at % of Fe, 5 to 15 at % of Ni, and the balance being Co.

With this alloy, the magnitude of the coupling magnetic field resulting from a Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction can be increased. In particular, the spin-flop magnetic field (Hsf) can be increased to approximately at least 293 kA/m. As a result, the magnetization directions of the magnetic sublayers39and41can be properly oriented antiparallel to each other. Moreover, by using the CoFeNi alloy satisfying the above-described composition ranges, the magnetostriction of the free magnetic layer28can be adjusted within the range of −3×10−6to 3×10−6, and the coercive force can be reduced to 790 A/m or less. Moreover, the soft magnetic characteristics of the free magnetic layer28can be improved.

When the free magnetic layer28has a synthetic ferrimagnetic structure, chromium atoms diffusing from the nonmagnetic layer32preferably exist in a region at the nonmagnetic-interlayer40side from the interface between the magnetic sublayer41and the second antiferromagnetic layer31. More preferably, a chromium-atom-free region exists in a region at the second-antiferromagnetic-layer-31-side from the interface between the magnetic sublayer41and the nonmagnetic interlayer40.

In this manner, the magnitude of the coupling exchange coupling magnetic field (Hex) between the magnetic sublayer41and the second antiferromagnetic layer31can be increased. Moreover, the magnitudes of the antiparallel coupling magnetic between the magnetic sublayer41and the magnetic sublayer with the nonmagnetic interlayer40therebetween resulting from the RKKY interaction can be increased. Thus, the unidirectional exchange bias magnetic fields (Hex*) at the two side portions of the free magnetic layer28can be increased compared to conventional techniques.

The unidirectional exchange bias magnetic field (Hex*) at the two side portions of the free magnetic layer28can still be increased when the chromium content at the interface between the magnetic sublayer41and the second antiferromagnetic layer31is larger than the chromium content at the interface between the nonmagnetic interlayer40and the magnetic sublayer41.

However, in order to increase the coupling magnetic field between the magnetic sublayer and the magnetic sublayer41as a result of the RKKY interaction, a chromium-free magnetic region preferably exists at the interface between the nonmagnetic interlayer40and the magnetic sublayer41.

FIG. 17is a partial enlarged cross-sectional view showing another example of the free magnetic layer28. As shown inFIG. 17, the free magnetic layer28has magnetic material sublayers42and44and a specular film43disposed between the magnetic material sublayers42and44. The specular film43may include defective parts (pinholes) G, as shown in FIG.18. The magnetic material sublayers42and44are magnetized in antiparallel to each other with the specular film43therebetween.

The magnetic material sublayers42and44is made of a magnetic material such as a NiFe alloy, a CoFe alloy, a CoFeNi alloy, elemental Co, or a CoNi alloy.

When the specular film43is in the free magnetic layer28, conduction electrons, such as spin-up conduction electrons, are specular-reflected at the specular film43while maintaining their spinning state, i.e., the energy and the quantum state. The reflected spin-up conduction electrons change the direction and can pass through the free magnetic layer.

Thus, the mean free path λ+of the spin-up conduction electrons can be increased by providing the specular film43. Accordingly, the difference between the mean free path λ+of the spin-up conduction electrons and the mean free path λ−of the spin-down conduction electrons can be widened, and the rate of change in resistance (ΔR/R) and the output can be improved.

The specular film43is made as follows. The layers up to the magnetic material sublayer42are first deposited, and the surface of the magnetic material sublayer42is oxidized. The oxidized part of the magnetic material sublayer42functions as the specular film43. The nonmagnetic material layer44is then deposited on the specular film43.

Examples of the material of the specular film43include oxides such as Fe—O, Ni—O, Co—O, Co—Fe—O, Co—Fe—Ni—O, Al—O, Al-Q-O (wherein Q is at least one selected from the group consisting of B, Si, N, Ti, V, Cr, Mn, Fe, Co, and Ni), and R—O (wherein R is at least one selected from the group consisting of Cu, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W); nitrides such as Al—N, Al-Q-N (wherein Q is at least one selected from the group consisting of B, Si, O, Ti, V, Cr, Mn, Fe, Co, and Ni), and R—N (wherein R is at least one selected from the group consisting of Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, and W); and Heusler alloys.

FIG. 18is a partial enlarged cross-sectional view of yet another example of the free magnetic layer28.

The free magnetic layer28shown inFIG. 18is constituted from a magnetic sublayer45and a back sublayer46. The back sublayer46is disposed between the magnetic sublayer45and the second antiferromagnetic layer31. The back sublayer46is made of, for example, Cu, Au, Cr, or Ru. The magnetic sublayer45is made of a magnetic material such as a NiFe alloy, a CoFe alloy, a CoFeNi alloy, elemental Co, or a CoNi alloy.

The back sublayer46is formed to extend the mean free path of the spin-up conduction electrons that contribute to the magnetoresistive effect. By a so-called spin-filter effect, the resulting magnetic sensing element exhibits a large rate of change in resistance and can meet the demand for higher recording densities. Since the back sublayer46functions as a medium for the exchange coupling, the magnitude of the exchange coupling magnetic field between the second antiferromagnetic layer31and the nonmagnetic material layer4may slightly decrease, but is still maintained at a sufficient magnitude.

Sixteenth Embodiment

FIG. 20shows a magnetic sensing element according to a sixteenth embodiment of the present invention. The magnetic sensing element shown inFIG. 20is based on the structures shown inFIGS. 10 and 19. In particular, the first insulating layer70is disposed on each of the upper faces33bof the third antiferromagnetic layers33, and the second insulating layer71is formed on the end33aof each third antiferromagnetic layer33and on the end of each of the second antiferromagnetic layers31. The lower shield layer (electrode)65composed of a magnetic material is disposed at the bottom of the composite film. The upper shield layer68is disposed to cover the first insulating layer70, the second insulating layer71, and the center portion D of the composite film.

Alternatively, the nonmagnetic layer69composed of a nonmagnetic conductive material such as Ta may be provided between the upper shield layer68and the first insulating layer70, between the upper shield layer68and the second insulating layer71, and between the center portion D of the composite film and the upper shield layer68, as indicated by a broken line in FIG.20.

The second antiferromagnetic layer31of each magnetic sensing element shown inFIGS. 1to14,19, and20is composed of, for example, a Cr-containing PtMn alloy, an Cr-containing X—Mn alloy, wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, or a Cr-containing Pt—Mn—X′ alloy, wherein X′ is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Ni, Ar, Ne, Xe, and Kr, may also be used to form the second antiferromagnetic layer31.

When the second antiferromagnetic layer31is composed of a PtMnCr alloy, X—Mn—Cr alloy, or a Pt—Mn—X—Cr alloy, the region around the interface between the second antiferromagnetic layer31and the free magnetic layer28can easily transform into an ordered structure by annealing. Thus, in such a case, the thickness of the second antiferromagnetic layer31is adjusted in the range of 5 to 10 Å so as to prevent the second antiferromagnetic layer31from transforming into an ordered structure prior to the formation of the third antiferromagnetic layer33.

In each of the above-described embodiments of the present invention, the nonmagnetic layer32is made of Cr. Alternatively, the nonmagnetic layer32may be made of at least one of Ti, Zr, Hf, V, Nb, Al, Si, Mo, W, Y, and rare earth elements.

FIGS. 21to23show steps of fabricating the magnetic sensing element show in FIG.1.FIGS. 21 and 23are partial cross-sectional viewed from the opposing face.

In the step shown inFIG. 21, the seed layer21, the first antiferromagnetic layer22, the pinned magnetic layer23, the nonmagnetic material layer27, the free magnetic layer28, the second antiferromagnetic layer31, and the nonmagnetic layer32are sequentially formed on the substrate20. These layers are formed by sputtering or vapor deposition. The pinned magnetic layer23shown inFIG. 21has, for example, a synthetic ferrimagnetic structure comprising the magnetic sublayers24and26composed of a CoFe alloy or the like and the nonmagnetic interlayer25composed of Ru. The nonmagnetic interlayer25is disposed between the magnetic sublayers24and26. The free magnetic layer28has, for example, a synthetic ferrimagnetic structure comprising the anti-diffusion sublayer29composed of a CoFe alloy or the like and the magnetic material sublayer30composed of a NiFe alloy.

Preferably, the first antiferromagnetic layer22is composed of a PtMn alloy, an X—Mn alloy, or a Pt—Mn—X′ alloy, wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, and X′ is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr.

Preferably, the second antiferromagnetic layer31is composed of a PtMn alloy, an X—Mn alloy, or a Pt—Mn—X′ alloy, wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, and X′ is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr.

The PtMn alloy and the X—Mn alloy preferably contain 37 to 63 at % of Pt and X, respectively. The PtMn alloy and the X—Mn alloy preferably contain 47 to 57 at % of Pt and X, respectively.

The Pt—Mn—X′ alloy preferably contains 37 to 63 at %, and, more preferably, 47 to 57 at % of X′+Pt. The Pt—Mn—X′ preferably contains 0.2 to 10 at % of X′. However, when the X′ is at least one of Pd, Ir, Rh, Ru, Os, Ni, and Fe, the X′ content is preferably in the range of 0.2 to 40 at %.

The thickness of the first antiferromagnetic layer22is preferably in the range of 80 to 300 Å. At such a thickness, a large exchange coupling magnetic field can be generated between the first antiferromagnetic layer22and the pinned magnetic layer23by field annealing. In particular, an exchange coupling magnetic field of 48 kA/m or more, for example, exceeding 64 kA/m can be generated.

The thickness of the second antiferromagnetic layer31is preferably in the range of 5 to 50 Å, more preferably, 10 to 50 Å, and most preferably 30 to 40 Å.

One of the features of the present invention is to form the second antiferromagnetic layer31at such a small thickness.

When the second antiferromagnetic layer31has a thickness of 50 Å or less, the second antiferromagnetic layer31exhibits nonantiferromagnetic properties. Thus, the second antiferromagnetic layer31rarely transforms into an ordered structure even after a first field annealing process described below. As a result, the exchange coupling magnetic field between the second antiferromagnetic layer31and the free magnetic layer28is small, if any. The magnetization direction of the free magnetic layer28is not as firmly pinned as the pinned magnetic layer23.

The thickness of the second antiferromagnetic layer31is preferably at least 5 Å, and more preferably at least 10 Å. Otherwise, the two side portions C of the second antiferromagnetic layer31do not easily exhibit antiferromagnetic properties even after the third antiferromagnetic layers33are formed. As a result, an exchange coupling magnetic field having a proper magnitude cannot be generated between the free magnetic layer28and the second antiferromagnetic layer31at the two side portions C.

Referring again toFIG. 21, the nonmagnetic layer32also prevents the second antiferromagnetic layer31from oxidation resulting from exposure to air.

The nonmagnetic layer32is made of Cr. The dense nonmagnetic layer32composed of Cr is rarely oxidized in the thickness direction by exposure to air. Thus, the thickness of the nonmagnetic layer32need not be large to prevent the oxidization of the second antiferromagnetic layer31. The thickness of the nonmagnetic layer32is preferably 2 to 10 Å, and more preferably 2 to 5 Å.

Another feature of the present invention is to form the nonmagnetic layer32with Cr at a small thickness such as approximately 2 to 10 Å. This allows low energy ion milling in the step shown in FIG.22. The milling process can be more accurately controlled, as will be described below in the step shown in FIG.22.

The layers up to the nonmagnetic layer32shown inFIG. 21disposed on the substrate20are then subjected to first field annealing. In particular, the layers are annealed at a first annealing temperature while applying a first magnetic field in a direction orthogonal to the track width direction, i.e., a first magnetic field in the Y direction orthogonal to the X direction. By the first field annealing, the exchange coupling magnetic field is generated between the first antiferromagnetic layer22and magnetic sublayer24of the pinned magnetic layer23, and the magnetic sublayer24is magnetized in the Y direction. The magnetic sublayer26is magnetized in a direction opposite to the Y direction by exchange coupling resulting from the RKKY interaction with the magnetic sublayer24. For example, the first annealing temperature is 270° C., and the magnitude of the applied magnetic field is 800 kA/m.

As described above, the magnitude of the exchange coupling magnetic field between the second antiferromagnetic layer31and the magnetic material sublayer30is small, if any. This is because the second antiferromagnetic layer31has a small thickness of 50 Å or less and thus does not exhibit antiferromagnetic properties.

Chromium atoms constituting the nonmagnetic layer32diffuse into the second antiferromagnetic layer31by the first field annealing. The region of the second antiferromagnetic layer31close to the interface with the nonmagnetic layer32thus contains Cr in addition to the material of the second antiferromagnetic layer31. The concentration of Cr is higher in the upper part of the second antiferromagnetic layer31than in the lower part of the second antiferromagnetic layer31. The Cr concentration gradually decreases toward the lower face of the second antiferromagnetic layer31. Such a gradual change in composition can be examined with a SIMS analyzer or the like.

Next, in the step shown inFIG. 22, a resist layer is formed on the upper face of the nonmagnetic layer32. The resist layer is exposed and developed so as to leave a resist layer49having the shape shown inFIG. 22on the nonmagnetic layer32. For example the resist layer49is a lift-off resist layer.

The two side portions32aof the nonmagnetic layer32not covered by the resist layer49are then partly removed by ion milling in the direction indicated by arrows H in FIG.22. Portions of the nonmagnetic layer32indicated by broken lines inFIG. 22are removed as a result.

The two side portions32aof the nonmagnetic layer32are partly removed for the following reasons. The thickness of the two side portions32amust be small in order to induce an antiferromagnetic interaction between the third antiferromagnetic layers33and the two side portions C of the second antiferromagnetic layer31in the subsequent step. Otherwise, the two side portions C of the second antiferromagnetic layer31do not exhibit antiferromagnetic properties, and the magnetization directions at the two side portions C of the free magnetic layer28cannot be firmly pinned.

The two side portions32aof the nonmagnetic layer32are preferably milled to a thickness of 3 Å or less, and more preferably 1.0 Å or less by ion milling. In this manner, an antiferromagnetic interaction can be induced between the two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layers33. As a result, the two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layers33can function as a single antiferromagnetic layer, and the two side portions C of the second antiferromagnetic layer31can exhibit antiferromagnetic properties. In order to protect the surfaces of the Cs of the second antiferromagnetic layer31, the thickness of the two side portions32ais preferably at least 0.2 Å (average thickness).

In the ion milling step shown inFIG. 22, low-energy ion milling is employed. This is because the nonmagnetic layer32has a small thickness of approximately 2 to 10 Å, and more preferably 2 to 5 Å.

According to a conventional process shown inFIG. 37that uses the Ta film9, the Ta film9itself is oxidized by exposure to air. Thus, the thickness of the Ta film9must be 30 to 50 Å in order to sufficiently protect the underlying layer from oxidizing. Since the volume of the Ta film9increases by the oxidation, the thickness of the Ta film9may exceed 50 Å. To remove the Ta film9of such a large thickness, high-energy ion milling must be performed. However, it is difficult to control the milling process to partly remove the Ta film9. The surface of the free magnetic layer5is often partly removed and suffers from damage due to the ion milling.

In the present invention, the thickness of the nonmagnetic layer32composed of Cr is approximately 2 to 10 Å, and 2 to 5 Å and still properly prevents the second antiferromagnetic layer31from being oxidized. Moreover, since low-energy ion milling is employed, it is easy to control the milling of the insulating layers33to stop partway.

Here, the term “low-energy ion milling” refers to ion milling employing ion beams having beam voltages (accelerating voltage) of less than 1,000 V. For example, beam voltages in the range of 100 to 500 V may be employed. In this embodiment, an Ar ion beam having a beam voltage of 200 V is used.

The time for milling is preferably approximately 20 to 40 seconds. The milling angle is 30 to 70 degrees, and more preferably 40 to 60 degrees with respect to an axis perpendicular to the surface of the substrate20. In this manner, the antiferromagnetic interaction between the two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layers33can be intensified, and the magnitudes of the exchange coupling magnetic fields generated between the second antiferromagnetic layer31and the free magnetic layer28at the two side portions C can be increased.

Next, the step shown inFIG. 23is performed. In this step, the third antiferromagnetic layer33and the electrode layer34are sequentially deposited on each of the two side portions32aof the nonmagnetic layer32by sputtering or vapor deposition. The ends33aof the third antiferromagnetic layers33and the ends32aof the electrode layers34are formed as flat or curved slopes so that the gap between the third antiferromagnetic layers33and the gap between the electrode layers34gradually increases along the Z direction.

In this embodiment, the gap between the lower portions of the third antiferromagnetic layers33determines the track width Tw.

The third antiferromagnetic layer33is preferably composed of the same antiferromagnetic material as that of the second antiferromagnetic layer31.

In the step shown inFIG. 23, the sum of the thickness of each third antiferromagnetic layer33and the thickness of the second antiferromagnetic layer31is preferably 80 to 300 Å. The thickness of the third antiferromagnetic layers33is preferably adjusted accordingly. At such a thickness, the two side portions C of the second antiferromagnetic layer31, which alone do not exhibit antiferromagnetic properties, readily exhibit antiferromagnetic properties.

After the electrode layers34are formed as shown inFIG. 23, the resist layer49along with layers33cand34bdeposited during the formation of the third antiferromagnetic layers33and the electrode layers34, respectively, is removed by lifting-off.

Next, a second field annealing is performed. This time, the magnetic field is applied in the track width direction (the X direction in the drawing). In the second field annealing, the applied magnetic field, i.e., the second magnetic field, is smaller than the exchange anisotropic magnetic field of the first antiferromagnetic layer22, and the annealing temperature is lower than the blocking temperature of the first antiferromagnetic layer22. The magnitude of the second magnetic field is preferably larger than the saturation magnetization field and the demagnetizing fields of the free magnetic layer28. In this manner, the exchange anisotropic magnetic field of the second antiferromagnetic layer31can be oriented in the track width direction (the X direction) without changing the direction of the exchange anisotropic magnetic field of the first antiferromagnetic layer22. The second annealing temperature is, for example 250° C., and the magnitude of the applied magnetic field is 24 kA/m.

Since the third antiferromagnetic layers33are formed on the two side portions C of the second antiferromagnetic layer31with the nonmagnetic layer32therebetween, the antiferromagnetic interaction between the second antiferromagnetic layer31and the third antiferromagnetic layers33is intensified, and the two side portions C of the second antiferromagnetic layer31, which alone do not exhibit antiferromagnetic properties, exhibit antiferromagnetic properties.

As a result, the two side portions C of the second antiferromagnetic layer31properly transform into an ordered structure by the second field annealing, and exchange coupling magnetic fields of proper magnitudes are produced between the free magnetic layer28and the second antiferromagnetic layer31at the two side portions C. Accordingly, the magnetization directions of the two side portions C of the free magnetic layer28are pinned in the track width direction (the X direction in the drawing).

The exchange coupling magnetic field is also generated between the second antiferromagnetic layer31and the free magnetic layer28at the side portion C by the second field annealing. However, the exchange coupling magnetic field is small, if any, and does not pin the magnetization direction of the center portion D of the free magnetic layer28as firmly as in the two side portions C.

The center portion D of the free magnetic layer28is moderately put in a single-magnetic-domain state. The magnetization direction in the center portion D can rotate in response to external magnetic fields.

Chromium atoms of the nonmagnetic layer32also diffuse into the second antiferromagnetic layer31and the third antiferromagnetic layers33as a result of the second field annealing. Thus, the second antiferromagnetic layer31and the third antiferromagnetic layer33after the second annealing contain chromium. The Cr concentration of the second antiferromagnetic layer31is higher in the upper part and lower in the bottom part. The Cr concentration of each third antiferromagnetic layer33is higher in the lower part and lower in the upper part. The Cr concentration in the second antiferromagnetic layer31gradually decreases along the direction opposite to the Z direction (the downward direction in the drawing). The Cr concentration in the third antiferromagnetic layer33gradually decreases along the Z direction (the upward direction in the drawing). Such a gradual change in concentration can be examined by a SIMS analyzer.

As the chromium atoms of the nonmagnetic layer32diffuse into the second antiferromagnetic layer31, the PtMn alloy, the X—Mn alloy, or the Pt—Mn—X′ alloy constituting the second antiferromagnetic layer31transforms into an ordered structure.

Since the nonmagnetic layer32is deposited on the second antiferromagnetic layer31to protect the second antiferromagnetic layer31, the thickness h1of the second antiferromagnetic layer31can be decreased to a thickness in the range of 5 to 50 Å, for example, approximately 10 Å. As Cr atoms diffuse into the second antiferromagnetic layer31having such a small thickness, the region around the interface between the second antiferromagnetic layer31and the free magnetic layer28rapidly transforms into an ordered structure, and the magnitude of the exchange coupling magnetic field at the interface can be increased.

Accordingly, in the resulting magnetic sensing element, the magnetization directions of the free magnetic layer28at the two side portions C can be firmly pinned by the two side portions C of the second antiferromagnetic layer31. Side reading can be reduced.

The crystal structure of the second antiferromagnetic layer31is, for example, of a CuAuI type. Chromium atoms diffusing from the nonmagnetic layer32partly replace the lattice points of the crystal lattice constituted from atoms of Pt and Mn, the crystal lattice constituted from atoms of X and Mn, or the crystal lattice constituted from atoms of Pt, Mn, and X′.

As described above, the magnetization direction of the free magnetic layer28can be properly controlled by employing the production method of the present invention. A magnetic sensing element having superior sensitivity compatible with narrower tracks can be produced.

A process for fabricating the magnetic sensing element shown inFIG. 2will now be described. The magnetic sensing element is made through the steps shown inFIGS. 21to23. During the step of ion milling shown inFIG. 22, the two side portions32aof the nonmagnetic layer32composed of Cr are completely removed. As is previously described, the thickness of the nonmagnetic layer32is so small that the nonmagnetic layer32can be milled by low-energy ion milling. Since the milling rate is low in the low-energy ion milling compared to high-energy ion milling, milling can be stopped immediately after the nonmagnetic layer32is completely removed. Thus, damage inflicted to the surface of the second antiferromagnetic layer31by milling can be minimized.

Since second antiferromagnetic layer31is not significantly affected by milling, the magnetic characteristics of the second antiferromagnetic layer31can be maintained at a satisfactory level.

The surface of the second antiferromagnetic layer31may be partly milled, as indicated by broken lines E in FIG.2. However, the surface of the second antiferromagnetic layer31is not significantly damaged. Thus, the two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layers33can function as a single antiferromagnetic layer, and the two side portions C of the second antiferromagnetic layer31can properly exhibit antiferromagnetic properties. When subjected to second field annealing, the two side portions C of the second antiferromagnetic layer31transform into an ordered structure, and exchange coupling magnetic fields are generated between the free magnetic layer28and the second antiferromagnetic layer31at the two side portions C. As a result the magnetization directions of the two side portions C of the free magnetic layer28can be pinned in the track width direction (the X direction).

The magnetic sensing element shown inFIG. 3can be manufactured by performing the step shown inFIG. 21, forming the resist layer49in the step shown inFIG. 22, and performing the step shown in FIG.23. In other words, no ion milling is performed during the step shown in FIG.22.

In order to make the magnetic sensing element shown inFIG. 3, the thickness of the nonmagnetic layer32is adjusted to be 3 Å or less, and more preferably 1 Å or less, in the step shown in FIG.21. Alternatively, the nonmagnetic layer32is deposited to a thickness of 2 to 10 Å, and more preferably 2 to 5 Å and is then milled to a thickness of 3 Å or less, and more preferably 1 Å or less by ion milling. The nonmagnetic layer32is preferably at least 0.2 Å in average thickness.

When the nonmagnetic layer32has a thickness of 3 Å or less, an antiferromagnetic interaction can be induced between the two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layers33. There is no need to completely remove or reduced to thickness of the two side portions32aof the nonmagnetic layer32by ion milling in the step shown in FIG.22.

The nonmagnetic layer32constituted from the center portion32band the two side portions32aof a uniform thickness can be formed through the steps described above.

When the free magnetic layer28having a structure shown inFIG. 16orFIG. 18is to be formed by this production method through steps shown inFIGS. 21to23, an additional step of covering the third antiferromagnetic layers33and the electrode layers34with a resist layer and removing the exposed center portion32bof the nonmagnetic layer32, the center portion of the second antiferromagnetic layer31, and the center portion of the magnetic sublayer41shown inFIG. 16or the back sublayer46shown inFIG. 19by ion milling or the like is provided.

The above description regards the methods for fabricating the CIP magnetic sensing elements shown inFIGS. 1to3. Methods for fabricating the CPP magnetic sensing elements shown inFIGS. 7to9will now be described. Only the steps different from those for fabricating the CIP magnetic sensing elements shown inFIGS. 1to3will be described below.

First, the steps shown inFIGS. 21 and 22are performed. Subsequently, in the step shown inFIG. 24, the third antiferromagnetic layers33are sputter-deposited on the two side portions32aof the nonmagnetic layer32. The sputtering is performed in the direction indicated by arrow N at a sputtering angle of θ1(an angle with respect to the axis parallel to the Z direction). The insulating layers67are then sputter-deposited over the upper face33band the ends33aof the third antiferromagnetic layer33. This sputtering is performed in the direction indicated by arrow K at a sputtering angle of θ2(an angle with respect to the axis parallel to the Z direction).

The angles θ1and θ2may be the same or different. Preferably, the sputtering angle θ2is larger than the sputtering angle θ1. In this manner, the ends67acan be extended over the two side ends of the center portion32bof the nonmagnetic layer32. Preferably, the angles θ1and θ2are not zero.

A method for fabricating the magnetic sensing element shown inFIG. 10will now be described.FIGS. 25to27are partial cross-sectional views of the magnetic sensing element viewed from the opposing face showing the steps of the fabrication method.

In the step shown inFIG. 25, the seed layer21, the first antiferromagnetic layer22, the pinned magnetic layer23, the nonmagnetic material layer27, the free magnetic layer28, the second antiferromagnetic layer31, and the nonmagnetic layer32are sequentially deposited on the substrate20by sputtering or vapor deposition. The pinned magnetic layer23inFIG. 25has a synthetic ferrimagnetic structure comprising the magnetic sublayers24and26composed of, for example, a CoFe alloy and the nonmagnetic interlayer25composed of, for example, Ru disposed between the magnetic sublayers24and26. The free magnetic layer28is constituted from the anti-diffusion sublayer29composed of, for example, a CoFe alloy and the magnetic material sublayer30composed of a NiFe alloy, for example.

The first antiferromagnetic layer22is preferably composed of a PtMn alloy, an X—Mn alloy, or a Pt—Mn—X′ alloy, wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, and X′ is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr.

The second antiferromagnetic layer31is preferably composed of a PtMn alloy, an X—Mn alloy, or a Pt—Mn—X′ alloy, wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, and X′ is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Cr, Ni, Ar, Ne, Xe, and Kr.

The PtMn alloy and the X—Mn alloy preferably contain 37 to 63 at % of Pt and X, respectively. The PtMn alloy and the X—Mn alloy preferably contain 47 to 57 at % of Pt and X, respectively.

The Pt—Mn—X′ alloy preferably contains 37 to 63 at %, and, more preferably, 47 to 57 at % of X′+Pt. The Pt—Mn—X′ preferably contains 0.2 to 10 at % of X′. However, when the X′ is at least one of Pd, Ir, Rh, Ru, Os, Ni, and Fe, the X′ content is preferably in the range of 0.2 to 40 at %.

The thickness of the first antiferromagnetic layer22is preferably in the range of 80 to 300 Å. At such a thickness, a large exchange coupling magnetic field can be generated between the first antiferromagnetic layer22and the pinned magnetic layer23by field annealing. In particular, an exchange coupling magnetic field of 48 kA/m or more, for example, exceeding 64 kA/m can be generated.

The thickness of the second antiferromagnetic layer31is preferably in the range of 5 to 50 Å, more preferably, 10 to 50 Å, and most preferably 30 to 40 Å.

One of the features of the present invention is to form the second antiferromagnetic layer31at such a small thickness.

When the second antiferromagnetic layer31has a thickness of 50 Å or less, the second antiferromagnetic layer31exhibits nonantiferromagnetic properties. Thus, the second antiferromagnetic layer31rarely transforms into an ordered structure even after a first field annealing process described below. As a result, the exchange coupling magnetic field between the second antiferromagnetic layer31and the free magnetic layer28is small, if any. The magnetization direction of the free magnetic layer28is not as firmly pinned as the pinned magnetic layer23.

The thickness of the second antiferromagnetic layer31is preferably at least 5 Å, and more preferably at least 10 Å. Otherwise, the two side portions C of the second antiferromagnetic layer31do not easily exhibit antiferromagnetic properties even after the third antiferromagnetic layers33are formed. As a result, an exchange coupling magnetic field having a proper magnitude cannot be generated between the free magnetic layer28and the second antiferromagnetic layer31at the two side portions C.

Referring again toFIG. 25, the nonmagnetic layer32also prevents the second antiferromagnetic layer31from oxidation resulting from exposure of the composite film to air.

The nonmagnetic layer32is made of Cr. The nonmagnetic layer32composed of Cr is dense and is rarely oxidized in the thickness direction by exposure to air. Thus, the thickness of the nonmagnetic layer32need not be large to prevent the oxidization of the second antiferromagnetic layer31. The thickness of the nonmagnetic layer32is preferably 2 to 10 Å, and more preferably to 5 Å.

Another feature of the present invention is to form the nonmagnetic layer32with Cr at a small thickness such as approximately 2 to 10 Å. This allows performance of low energy ion milling, which is relatively easy to control, in the subsequent step.

Referring again toFIG. 25, after the layers up to the nonmagnetic layer32are deposited on the substrate20, first field annealing is performed. In particular, the layers are annealed at a first annealing temperature while applying a first magnetic field in a direction orthogonal to the track width direction, i.e., a first magnetic field in the Y direction orthogonal to the X direction. By the first field annealing, the exchange coupling magnetic field is generated between the first antiferromagnetic layer22and magnetic sublayer24of the pinned magnetic layer23, and the magnetic sublayer24is magnetized in the Y direction. The magnetic sublayer26is magnetized in a direction opposite to the Y direction by exchange coupling resulting from the RKKY interaction with the magnetic sublayer24. For example, the first annealing temperature is 270° C., and the magnitude of the applied magnetic field is 800 kA/m.

As described above, the second antiferromagnetic layer31rarely transforms into an ordered structure by the first field annealing since the thickness is small, and the magnitude of the exchange coupling magnetic field between the second antiferromagnetic layer31and the magnetic material sublayer30is small, if any. This is because the second antiferromagnetic layer31has a small thickness of 50 Å or less and thus does not exhibit antiferromagnetic properties.

Chromium atoms constituting the nonmagnetic layer32diffuse into the second antiferromagnetic layer31by the first field annealing. The region of the second antiferromagnetic layer31close to the interface with the nonmagnetic layer32thus contains Cr in addition to the material of the second antiferromagnetic layer31. The concentration of Cr is higher in the upper part of the second antiferromagnetic layer31than in the lower part of the second antiferromagnetic layer31. The Cr concentration gradually decreases toward the lower face of the second antiferromagnetic layer31. Such a gradual change in composition can be examined with a SIMS analyzer or the like.

Next, in the step shown inFIG. 25, the entire surface of the nonmagnetic layer32is partly milled with ions to the position indicated by broken line J.

The nonmagnetic layer32is partly milled for the following reasons. The thickness of the nonmagnetic layer32must be small in order to induce an antiferromagnetic interaction between the third antiferromagnetic layers33and the two side portions C of the second antiferromagnetic layer31in the subsequent step. Otherwise, the magnetization direction of the free magnetic layer28cannot be properly controlled.

The two side portions32aof the nonmagnetic layer32are preferably milled to a thickness (average thickness) in the range of 0.2 to 3 Å, and more preferably 0.2 to 1.0 Å by ion milling. In this manner, an antiferromagnetic interaction can be induced between the two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layers33. As a result, the two side portions C of the second antiferromagnetic layer31and the third antiferromagnetic layers33can function as a single antiferromagnetic layer, and the two side portions C of the second antiferromagnetic layer31can exhibit antiferromagnetic properties.

In the ion milling step shown inFIG. 25, low-energy ion milling can be employed. This is because the nonmagnetic layer32after deposition has a small thickness of approximately 2 to 10 Å. Thus, milling of the nonmagnetic layer32can be stopped partway. In other words, milling can be more accurately controlled compared to conventional techniques.

Alternatively, the nonmagnetic layer32may be completely removed in the step shown in FIG.25. Although no nonmagnetic layer32physically exists, chromium atoms are diffused in the second antiferromagnetic layer31. The Cr concentration increases toward the upper face of the second antiferromagnetic layer31.

Next, in the step shown inFIG. 26, the third antiferromagnetic layer33is formed on the nonmagnetic layer32, and the interlayer (protective layer)35composed of Ta or the like is sequentially formed on the third antiferromagnetic layer33. The interlayer35protects the third antiferromagnetic layer33from being oxidized by exposure to air.

Preferably, the third antiferromagnetic layer33and the second antiferromagnetic layer31are composed of the same material.

In the step shown inFIG. 26, the sum of the thickness of the third antiferromagnetic layer33and the thickness of the second antiferromagnetic layer31is preferably 80 to 300 Å. The thickness of the third antiferromagnetic layer33is preferably adjusted accordingly. At such a thickness, the second antiferromagnetic layer31, which alone does not exhibit antiferromagnetic properties, exhibits antiferromagnetic properties.

In the subsequent step shown inFIG. 27, a mask layer50composed of, for example, an inorganic material is formed on the interlayer35. The mask layer50has a predetermined void50a. Examples of the inorganic material include Ta, Ti, Si, Zr, Nb, Cr, Mo, Hf, W, Al—O, Al—Si—O, and Si—O. In case the mask layer50is made of a metal, the mask layer50may be left to function as the electrode layers34.

The mask layer50may be prepared as follows. A resist layer (not shown) is disposed on the center portion of the interlayer35, and the two sides of the resist layer are filled with the material of the mask layer50. The resist layer is then removed so as to form the gap50aof a predetermined with and the mask layer50. Alternatively, the mask layer50may be provided on the entire surface of the interlayer35, and a resist layer (not shown) may be formed on the mask layer50. A hole is formed at the center portion of the resist layer by exposure and development, and part of the mask layer50exposed at the hole is removed by reactive ion etching or the like so as to form the void50a.

In the present invention, the mask layer50may be composed of a resist material.

In the step shown inFIG. 27, the interlayer35exposed at the void50ain the mask layer50, and part of the third antiferromagnetic layer33is removed by reactive ion etching or ion milling. Milling is performed down to a position indicated by broken line K in the drawing. The milling is preferably performed until the sum of the thickness of the third antiferromagnetic layer33in the center portion D and the thickness of the second antiferromagnetic layer31reaches a thickness in the range of 5 to 50 Å, and more preferably 10 to 50 Å. Otherwise, the center portion D of the second antiferromagnetic layer31exhibits antiferromagnetic properties, an exchange coupling magnetic field is generated between the second antiferromagnetic layer31and the free magnetic layer28at the center portion D, and the magnetization direction of the free magnetic layer28at the center portion D is firmly pinned in a certain direction.

When the third antiferromagnetic layer33is milled partway as indicated by broken line K inFIG. 27, the magnetic sensing element shown inFIG. 5can be manufactured.

Alternatively, all of the third antiferromagnetic layer33exposed at the void50aof the mask layer50may be removed, and the nonmagnetic layer32may be exposed at the void50a. Here, the nonmagnetic layer32may be milled partway. When milling is stopped at the moment the nonmagnetic layer32is exposed at the void50a, the magnetic sensing element shown inFIG. 4is manufactured.

Alternatively, all of the nonmagnetic layer32exposed at the void50amay be removed, and the second antiferromagnetic layer31may be milled partway until the position indicated by a single-dotted chain line L is reached. In this manner, the magnetic sensing element shown inFIG. 6is manufactured.

As shown inFIG. 27, the third antiferromagnetic layer33is milled in a direction perpendicular to the surface of the substrate20. Thus, the ends33aof the third antiferromagnetic layer33are perpendicular to the surface of the substrate20. In other words, the ends33aextend in the Z direction. In case the layers below the third antiferromagnetic layer33are milled, the ends of these layers are, as a matter of course, also perpendicular to the surface of the substrate20.

Note that in order to form ends50bof the mask layer50as flat or curved slopes so that the gap between the ends50bgradually increases along the Z direction (the upward direction), as indicated by broken lines M, the milling direction is shifted from the axis perpendicular to the surface of the substrate20. Since the gap between the ends33aof the third antiferromagnetic layer33gradually decreases toward the bottom, the track width Tw can be made smaller than the width of the void50ain the mask layer50. Thus, a magnetic sensing element that can meet the demand for narrower tracks can be manufactured.

The second antiferromagnetic layer31may be milled until a desired position is reached. However, the thickness of the second antiferromagnetic layer31in the center portion D should be sufficiently small so as not to exhibit antiferromagnetic properties. Moreover, the free magnetic layer28must not be milled by reaction ion etching or ion milling because the magnetic characteristics of the free magnetic layer28will be degraded by damage inflicted by milling.

In the embodiment shown inFIG. 19, the magnetic sublayer41may be completely removed, and the nonmagnetic interlayer40may be milled partway. When the free magnetic layer28having the structure shown inFIG. 18is employed, the back sublayer46may be milled partway.

Subsequent to the RIE or ion milling, a second field annealing is performed. This time, the magnetic field is applied in the track width direction (the X direction in the drawing). In the second field annealing, the applied magnetic field, i.e., the second magnetic field, is smaller than the exchange anisotropic magnetic field of the first antiferromagnetic layer22, and the annealing temperature is lower than the blocking temperature of the first antiferromagnetic layer22. The magnitude of the second magnetic field is preferably larger than the saturation magnetization field and the demagnetizing fields of the free magnetic layer28. In this manner, the exchange anisotropic magnetic field of the second antiferromagnetic layer31at the two side portions C can be oriented in the track width direction (the X direction) without changing the direction of the exchange anisotropic magnetic field of the first antiferromagnetic layer22. The second annealing temperature is, for example 250° C., and the magnitude of the applied magnetic field is 24 kA/m.

The two side portions C of the second antiferromagnetic layer31exhibit antiferromagnetic properties due to an antiferromagnetic interaction with the third antiferromagnetic layers33formed on the second antiferromagnetic layer31. By the second field annealing, the two side portions C of the second antiferromagnetic layer31transform into an ordered structure, and large exchange coupling magnetic fields are generated between the free magnetic layer28and the second antiferromagnetic layer31at the two side portions C. As a result, the magnetization directions of the two side portions C of the free magnetic layer28are pinned in the track width direction (the X direction).

Since the antiferromagnetic layer disposed on the center portion D of the free magnetic layer28is thin and thus does not exhibit antiferromagnetic properties, the second antiferromagnetic layer31at the center portion D does not transform into an ordered structure by the second field annealing. Therefore, only a small exchange coupling magnetic field is generated, if any, between the free magnetic layer28and the second antiferromagnetic layer31at the center portion D. The center portion D of the free magnetic layer28is not pinned as firmly as in the two side portions C.

The center portion D of the free magnetic layer28is only moderately put in a single-magnetic-domain state so that the magnetization direction thereof can rotate in response to external magnetic fields.

According to present invention described above, the magnetization direction of the free magnetic layer28can be properly controlled, and a magnetic sensing element having a high sensitivity even with narrow tracks can be manufactured.

Chromium atoms of the nonmagnetic layer32also diffuse into the second antiferromagnetic layer31and the third antiferromagnetic layers33as a result of the second field annealing. Thus, the second antiferromagnetic layer31and the third antiferromagnetic layer33after the second annealing contain chromium. The Cr concentration of the second antiferromagnetic layer31is higher in the upper part and lower in the bottom part. The Cr concentration of each third antiferromagnetic layer33is higher in the lower part and lower in the upper part. The Cr concentration in the second antiferromagnetic layer31gradually decreases along the direction opposite to the Z direction (the downward direction in the drawing). The Cr concentration in the third antiferromagnetic layer33gradually decreases along the Z direction (the upward direction in the drawing). Such a gradual change in concentration can be examined by a SIMS analyzer.

As the chromium atoms of the nonmagnetic layer32diffuse into the second antiferromagnetic layer31, the PtMn alloy, the X—Mn alloy, or the Pt—Mn—X′ alloy constituting the second antiferromagnetic layer31rapidly transforms into an ordered structure.

Since the nonmagnetic layer32is deposited on the second antiferromagnetic layer31to protect the second antiferromagnetic layer31, the thickness h1of the second antiferromagnetic layer31can be decreased to a thickness in the range of 5 to 50 Å, for example, approximately 10 Å. As Cr atoms diffuse into the second antiferromagnetic layer31having such a small thickness, the region around the interface between the second antiferromagnetic layer31and the free magnetic layer28rapidly transforms into an ordered structure, and the magnitude of the exchange coupling magnetic field at the interface can be increased.

Accordingly, in the resulting magnetic sensing element, the magnetization directions of the free magnetic layer28at the two side portions C can be firmly pinned by the two side portions C of the second antiferromagnetic layer31. Side reading can be reduced.

The crystal structure of the second antiferromagnetic layer31is, for example, of a CuAuI type. Chromium atoms diffusing from the nonmagnetic layer32partly replace the lattice points of the crystal lattice constituted from atoms of Pt and Mn, the crystal lattice constituted from atoms of X and Mn, or the crystal lattice constituted from atoms of Pt, Mn, and X′.

The second field annealing may be performed after the step shown inFIG. 26, i.e., the step of forming the third antiferromagnetic layer33and the interlayer35on the nonmagnetic layer32. Since the second antiferromagnetic layer31exhibits antiferromagnetic properties because of the third antiferromagnetic layers33thereon, the second antiferromagnetic layer31transforms to an ordered structure by the second field annealing. As a result, a large exchange coupling magnetic field is generated between the second antiferromagnetic layer31and the free magnetic layer28and pins the magnetization direction of the free magnetic layer28in the track width direction. However, since the center portion D of the third antiferromagnetic layer33and the second antiferromagnetic layer31are milled in the step shown inFIG. 27, the exchange coupling magnetic field between the free magnetic layer28and the center portion D of the second antiferromagnetic layer31weakens. Accordingly, the magnetization direction of the center portion D of the free magnetic layer28is moderately oriented so as to be responsive to external magnetic fields.

FIG. 28is an enlarged partial cross-sectional view from the opposing face.FIG. 28shows a step of fabricating the electrode layer34.

When the mask layer50shown inFIG. 27is composed of a resist material and thus cannot be used as an electrode, the electrode layer34must be formed on each third antiferromagnetic layer33after the removal of the mask layer50.

As shown inFIG. 28, a resist layer51is formed in the void50ain the third antiferromagnetic layer33over part of the upper faces of the third antiferromagnetic layers33. Alternatively, the resist layer51may be formed only inside the void50a. The electrode layers34are deposited on part of the third antiferromagnetic layers33not covered by the resist layer51. Subsequently, the resist layer51is removed.

The above description regards the method for fabricating the CIP magnetic sensing elements shown inFIGS. 4to6. Methods for fabricating the CPP magnetic sensing elements shown inFIGS. 11 and 12will now be described. Only the steps different from those for fabricating the magnetic sensing elements shown inFIGS. 4to6are described below.

After the step shown inFIG. 25, the first insulating layer70is sequentially sputter-deposited on the third antiferromagnetic layer33in the step shown in FIG.26.

As shown inFIG. 29, a resist layer80having a void80aat the center in the track width direction (the X direction) is formed on the first insulating layer70by exposure and development.

Part of the first insulating layer70and the third antiferromagnetic layer33not covered with the base layer80is milled in the direction indicated by arrows O by ion milling or reactive ion etching (RIE) so as to remove the layers indicated by broken lines in FIG.29. How far the milling is performed determines which of the embodiments shown inFIGS. 10to12is made.

Alternatively, the first insulating layer70may be formed on each of the two side portions C of the third antiferromagnetic layer33, and the exposed center portion D of the third antiferromagnetic layer33may be milled using the first insulating layers70as a mask.

Although the ends80bof the resist layer80shown inFIG. 29are perpendicular to the surface of the substrate20, the ends80B may be flat or curved slopes. The beam incident angle of the ion milling may be shifted from the axis normal to the substrate surface. In these cases, the ends33aof the third antiferromagnetic layers33are formed as flat or curved slopes. Subsequently, the resist layer80is removed.

In the step shown inFIG. 30, the second insulating layer71is formed over the first insulating layers70, the ends of the third antiferromagnetic layers33, and the center portion D of the magnetic sensing element. The second insulating layer71is formed by sputter-depositing an insulating material such as Al2O3, SiO2, AlN, Al—Si—O—N, Al—Si—O, Ti2O3, Ti3O5, or Ta2O5. Ion beam sputtering, long through sputtering, collimation sputtering, or the like may be employed.

The sputtering angle θ3(an angle with respect to the axis in the Z direction) for forming the second insulating layer71is important. As shown inFIG. 30, the sputtering direction P has the sputtering angle of θ3with respect to the direction perpendicular to the surface of each layer constituting the composite film. In the present invention, the sputtering angle θ3is preferably as large as possible so that the second insulating layer71can be formed on the ends33aof the third antiferromagnetic layer33. For example, the sputtering angle θ3is 50 to 70 degrees.

At a large sputtering angle θ3, the thickness T3of the second insulating layer71on the ends33aof the third antiferromagnetic layer33in the track width direction (the X direction) can become larger than the thickness T4of the second insulating layer71on the upper face of the magnetic sensing-element and the first insulating layers70. If the thickness of the second insulating layer71is not adjusted as above, the second insulating layer71on the ends33aof the third antiferromagnetic layers33will be completely removed in the subsequent ion milling step. Even when the second insulating layer71remains on the ends33aof the third antiferromagnetic layers33, the thickness thereof is so small that the second insulating layer71no longer functions as an insulating layer for decreasing the shunt loss.

Next, as shown inFIG. 30, ion milling is performed in direction Q perpendicular or substantially perpendicular to the surface of each layer of the composite film (in the Z direction). The milling angle is approximately 0 to 20 degrees with respect to the surface of each layer of the composite film. The ion milling is performed until the second insulating layer71formed on the center portion D is properly removed. As a result, the second insulating layer71formed on the upper faces33bof the third antiferromagnetic layers33are also removed. On the other hand, the second insulating layer71on the ends33aof the third antiferromagnetic layers33remains even after the ion milling. This is because the thickness T3of the second insulating layer71on the ends33ais larger than that on the center portion D of the magnetic sensing element, and ion milling in the milling direction Q does not mill the second insulating layer71on the ends33aas much as the second insulating layer71at the center portion D of the magnetic sensing element. Thus, the second insulating layers71having a proper thickness can be formed on the ends33aof the third antiferromagnetic layer33.

Such a state is shown in FIG.31. The thickness T3of the second insulating layer71on the end33aof the third antiferromagnetic layer33in the track width direction is approximately 5 to 10 nm.

As shown inFIG. 31, the upper face33bof each third antiferromagnetic layer33is covered by the first insulating layer70, and each end33aof the third antiferromagnetic layer33is covered by the second insulating layer71. If necessary, the nonmagnetic layer69shown inFIG. 10may be provided over the first insulating layers70, the second insulating layers71, and the center portion D of the magnetic sensing element, and the upper shield layer68, which functions as an upper electrode, may then be formed by plating.

According to this method, a CPP magnetic sensing element that can properly decrease the shunt loss from the current supplied from the shield layers can be obtained.

In the magnetic sensing elements shown inFIGS. 13 and 14, the protrusion65ais formed in the lower shield layer65, and the insulating layers78are formed between the seed layer21and the two side portions65bof the lower shield layer65. First, the lower shield layer65is formed by plating, sputtering, or the like, and is planarized by polishing. A resist layer is then formed on the center portion of the lower shield layer65in the track width direction, and the two side portions65bof the lower shield layer65is milled partway by ion milling. Thus, the protrusion65ais formed at the center of the lower shield layer65in the track width direction.

Next, the insulating layers78are formed by sputtering on the two side portions65bof the lower shield layer65not covered by the resist layer. This sputter deposition is stopped when the upper faces of the insulating layers78become flush with the upper face65a1of the protrusion65a. After the resist layer is removed, the upper face65a1of the protrusion65aand the upper faces of the insulating layers78may be polished by chemical mechanical polishing so as to provide highly planarized surface. In such a case, the first polishing process is not necessary.

The second antiferromagnetic layer31above may be composed of a Cr-containing PtMn alloy, a Cr-containing X—Mn alloy, wherein X is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Os, Ni, and Fe, or a Cr-containing Pt—Mn—X′ alloy, wherein X′ is at least one element selected from the group consisting of Pd, Ir, Rh, Ru, Au, Ag, Os, Ni, Ar, Ne, Xe, and Kr.

When the second antiferromagnetic layer31is composed of a PtMnCr alloy, X—Mn—Cr alloy, or a Pt—Mn—X′—Cr alloy, the thickness of the second antiferromagnetic layer31is adjusted in the range of 5 to 30 Å so as to prevent the second antiferromagnetic layer31from transforming into an ordered structure prior to the formation of the third antiferromagnetic layer33.

Although the nonmagnetic layer32above is made of Cr, the nonmagnetic layer32may be made of at least one of Ti, Zr, Hf, V, Nb, Al, Si, Mo, W, Y, and rare earth elements.

In fabricating a magnetic head using the CIP magnetic sensing element described above, an underlayer composed of an insulating material such as alumina is provided between the substrate20and the seed layer21, a lower shield layer composed of a magnetic alloy is deposited on the underlayer, and a lower gap layer composed of an insulating material is deposited on the lower shield layer. The magnetic sensing element is then formed on the lower gap layer. An upper gap layer composed of an insulating material is then formed on the magnetic sensing element, and an upper shield layer composed of a magnetic alloy is formed on the upper gap layer. Optionally, an inductive write head may be formed on the upper shield layer.

The magnetic sensing element of the present invention can be incorporated into a magnetic sensor as well as a magnetic head installed in a hard disk device.

EXAMPLES

Experiments were conducted to demonstrate that the magnitude of the exchange coupling magnetic field between the second antiferromagnetic layer31and the free magnetic layer28increases by field-annealing the composite film having the chromium nonmagnetic layer32disposed between the second antiferromagnetic layer31and the third antiferromagnetic layer33.

FIG. 32is a graph showing the relationship between the exchange coupling magnetic field and the thickness of the chromium layer inserted at a position 5 Å away from the interface between the ferromagnetic layer and the antiferromagnetic layer.

This experiment was conducted to show the effect of changes in thickness of the nonmagnetic layer32between the second antiferromagnetic layer31having a thickness of 5 Å and the third antiferromagnetic layer33on the exchange coupling magnetic field (Hex) between the free magnetic layer28and the second antiferromagnetic layer31.

The thickness of the Cr layer was in terms of the average thickness. The average thickness can be determined by, for example, X-ray fluorescence analysis.

The average thickness of the Cr layer is sometimes less than 1 Å. As is widely known, no uniform thin film has a thickness of less than 1 Å since 1 Å corresponds to the diameter of one atom or less. However, in a nonuniform thin film containing unevenly distributed Cr atoms, there exist regions with chromium atoms and regions without any chromium atoms. Accordingly, the average thickness of the chromium layer is sometimes less than 1 Å.

The composite film was annealed at 290° C. for 4 hours while applying a magnetic field of 800 kA/m.

The exchange coupling magnetic field Hex without the Cr layer in the antiferromagnetic layer was 93 kA/m.

The Cr layer was positioned in the antiferromagnetic layer 5 Å away from the interface between the antiferromagnetic layer and the pinned magnetic layer. The exchange coupling magnetic field Hex between the antiferromagnetic layer (Pt50Mn50) and the ferromagnetic layer (Co90Fe10) was 152 to 160 kA/m when the thickness of the Cr layer was in the range of 0.2 to 1.0 Å.

Next, the Cr layer having a thickness of 0.2 Å was disposed at various positions in the antiferromagnetic layer. The resulting exchange coupled film was annealed, and the exchange coupling energy Jk after annealing was examined.

This experiment was conducted to examine the effect on the exchange coupling energy Jk between the free magnetic layer28and the second antiferromagnetic layer31when the nonmagnetic layer32having a thickness of 0.2 Å was disposed between the second antiferromagnetic layer31and the third antiferromagnetic layer33and when the thickness of the second antiferromagnetic layer31was varied.

The layer structure of the composite film used in the experiment is shown below. The Cr layer is omitted.

The composite film was annealed at 290° C. for 4 hours while applying a magnetic field of 800 kA/m.

The results are shown in FIG.33. The abscissa axis indicates the position where the Cr layer is disposed. In the graph shown inFIG. 33, the position at the interface between the antiferromagnetic layer (Pt50Mn50) and the ferromagnetic layer (Co90Fe10) is assumed as a zero distance. The negative distance is indicated when the Cr layer is in the antiferromagnetic layer. For example, the position of the Cr layer is −5 Å when the Cr layer is provided in the antiferromagnetic layer at a position 5 Å away from the interface. In this experiment, the distance from the interface to the Cr layer corresponded to the thickness of the second antiferromagnetic layer31in the magnetic sensing element of the present invention.

The exchange coupling energy Jk between the antiferromagnetic layer and the pinned magnetic layer without Cr layer in the antiferromagnetic layer was 0.222 mJ/m2after annealing.

When the Cr layer in the antiferromagnetic layer was 5 Å away from the interface, i.e., when the second antiferromagnetic layer31had a thickness of 5 Å, the exchange coupling energy Jk was 0.370 mJ/m2. When the Cr layer in the antiferromagnetic layer was 10 Å away from the interface, the exchange coupling energy Jk was 0.330 mJ/m2. When the Cr layer in the antiferromagnetic layer was 20 Å away from the interface, the exchange coupling energy Jk was 0.245 mJ/m2. Even when the Cr layer in the antiferromagnetic layer was more than 20 Å away from the interface, the exchange coupling energy Jk did not decrease significantly.

FIG. 34is a graph plotted by converting the abscissa axis of the graph inFIG. 33in terms of the exchange coupling magnetic field (Hex) between the ferromagnetic layer and the antiferromagnetic layer.

The curve inFIG. 34indicating changes in exchange coupling magnetic field (Hex) versus the position of the Cr layer was substantially identical to the curve inFIG. 33indicating the exchange coupling energy Jk.

The results described above fully demonstrate that an exchange coupled film including a Cr layer in an antiferromagnetic layer generates a larger exchange coupling energy Jk than an exchange coupled film without any Cr layer.

In other words, when the Cr nonmagnetic layer32is provided between the second antiferromagnetic layer31and the third antiferromagnetic layer33, the exchange coupling magnetic field and the exchange coupling energy Jk with the free magnetic layer28increase.

FIG. 35is a graph indicating the unidirectional exchange bias magnetic field (Hex*) of an exchange coupled film after annealing when a Cr layer 0.2 Å in thickness was disposed at various positions in an antiferromagnetic layer. The exchange coupled film used in the experiment was prepared by laminating the antiferromagnetic layer with a ferromagnetic layer constituted from first and second magnetic sublayers and a nonmagnetic interlayer disposed between the first and second magnetic sublayers.

This experiment was conducted to examine the effect of the thickness of the second antiferromagnetic layer31on the unidirectional exchange bias magnetic field (Hex*) between the synthetic ferrimagnetic free magnetic layer28and the second antiferromagnetic layer31when the nonmagnetic layer320.2 Å in thickness was provided between the second antiferromagnetic layer31and the third antiferromagnetic layer33.

The layer structure of the composite film used in the experiment is shown below. The Cr layer is omitted.

The composite film was annealed at 290° C. for 4 hours while applying a magnetic field of 800 kA/m.

The abscissa axis inFIG. 35indicates the position where the Cr layer is provided. In the graph shown inFIG. 35, the position at the interface between the antiferromagnetic layer and the ferromagnetic layer is assumed as a zero distance. The negative distance is indicated when the Cr layer is in the antiferromagnetic layer. For example, the position of the Cr layer is −5 Å when the Cr layer is provided in the antiferromagnetic layer at a position 5 Å away from the interface.

The experiment demonstrated that the exchange-coupled film including the Cr layer in the antiferromagnetic layer exhibited a unidirectional exchange bias magnetic field (Hex*) in the range of 148 to 152 kA/m regardless of the position of the Cr layer.

In view of the above, stable unidirectional exchange coupling magnetic fields (Hex*) can be generated using the synthetic ferrimagnetic free magnetic layer even when the thickness of the second antiferromagnetic layer31is changed.