Laminated return pole for suppressing side track erasure

A perpendicular writer includes a surface, a main pole proximate the surface, a return pole proximate the surface, and a back yoke connecting the main pole to the return pole distal the surface. The return pole is configured such that a magnetization of a portion of the return pole adjacent the surface is held substantially parallel to the surface during a write operation.

BACKGROUND OF THE INVENTION

The present invention relates generally to the field of electronic data storage and retrieval, and more particularly to a perpendicular magnetic writer having a return pole that is laminated to suppress side track erasure.

In an electronic data storage and retrieval system, a transducing head typically includes a writer for storing magnetically-encoded information on a magnetic medium and a reader for retrieving that magnetically-encoded information from the magnetic medium. The reader typically includes two shields and a magnetoresistive (MR) sensor positioned between the shields. Magnetic flux from the surface of the magnetic medium causes rotation of the magnetization vector of a sensing layer of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. This change in resistivity of the MR sensor can be detected by passing a current through the MR sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary.

For a perpendicular recording head, the writer typically includes a main pole and a return pole which are connected to each other at a back end by a back yoke (or back via), and which are separated from each other at a surface of the writer opposite the back end by a gap layer. One or more layers of conductive coils are positioned between the main and return poles and are encapsulated by insulating layers. Often, the writer and the reader are arranged in a merged configuration in which a shared pole serves as both the top shield of the reader and the return pole of the writer. Alternately, the writer and reader may be arranged in a piggy back configuration in which top shield of the reader and the return pole of the writer are separated by a layer of a nonmagnetic material.

A perpendicular recording medium for use with a perpendicular recording head includes a storage layer and soft underlayer. The storage layer of the medium preferably has a high coercivity and perpendicular anisotropy; that is, its magnetization is preferably held in a direction substantially normal to a surface of the medium. The soft magnetic underlayer of the medium preferably has a high permeability and a substantially in-plane orientation of the easy axis.

To write data to the perpendicular magnetic medium, an electric current is caused to flow through the conductive coils to induce a magnetic field across the write gap between the main and return poles. In operation, the underlayer of the magnetic medium acts as a third pole of the writer such that the magnetic field bridges two gaps—the gap between the main pole and the underlayer and the gap between the underlayer and the return pole—with the magnetic field passing twice through the storage layer of the magnetic media. As connoted by their names, the main pole is used to physically write data to the magnetic medium, while the return pole provides only a return path for the magnetic field generated by the main pole. Thus, the magnetic field traversing the gap between the main pole and the underlayer is preferably strong enough to cause a bit to be recorded to the media while the magnetic field traversing the gap between the underlayer and the return pole is not.

To ensure that the magnetic field traversing the gap between the underlayer of the medium and the return pole does not contribute to the data written to the magnetic medium, the return pole conventionally has been formed of a lower magnetic moment material than the main pole and has been configured with a larger area at the media facing surface than the main pole.

Despite this larger surface area, the strength of the magnetic field affecting the magnetic medium under the return pole is nonetheless sufficient to overcome a nucleation field of magnetic medium. This results because the magnetic flux throughout the cross-section of the return pole is not uniform, but is instead concentrated along the edges of each element of the writer. This concentration along the edges is caused by various factors, including surface anisotropy, an edge pinning effect, and a skin effect. Further, this concentration of magnetic flux at the edges of the return pole may result in a sizable magnetic field being produced at the edges of the return pole when the write current is on. In fact, the magnetic field may be as great as 10-80% of the saturation magnetic flux density (Bs) of the return pole's soft materials. Further, this magnetic field may be large enough to cause undesired side track erasure on the magnetic medium. To the extent that the field is not strong enough to actually erase the magnetic medium below the return pole, the side-writing may be significant enough to accelerate the magnetization decay process, leading to a non-negligible threat to the long term data retention of the magnetic medium

BRIEF SUMMARY OF THE INVENTION

A perpendicular writer includes a surface, a main pole proximate the surface, a return pole proximate the surface, and a back yoke connecting the main pole to the return pole distal the surface. The return pole is configured such that a magnetization of a portion of the return pole adjacent the surface is held substantially parallel to the surface during a write operation.

DETAILED DESCRIPTION

The present invention is a perpendicular writer that suppresses the concentration of magnetic flux at the edges of a return pole of the writer adjacent a surface of the writer opposite a back via of the writer. To accomplish this goal, the writer is configured to cause the magnetization of the return pole adjacent the surface to be oriented in a direction substantially parallel to the surface during a write operation. Preferably, the magnetization direction is less than a 4° departure from parallel, and more preferably, less than a 2° departure.

FIG. 1is a cross-sectional view of perpendicular writer60in accord with a first embodiment of the present invention. Writer60has a yoke-return pole configuration and includes main pole62, return pole64, and back yoke66. In the embodiment shown, main pole62further includes main pole tip68positioned adjacent main pole yoke72, with main pole tip68extending to surface70of writer60and main pole yoke72preferably recessed a distance from surface70. In other embodiments, main pole yoke72is omitted from main pole62. Main pole62is separated from return pole64at surface70by a write gap and is connected to return pole64distal to surface70by back yoke66. To write data to a magnetic medium, an electric current is caused to flow through a conductive coil (not shown) wrapped about back yoke66or main pole yoke72, which in turn produces a magnetic field in main pole62, return pole64, and back yoke66.

Portion74of return pole64is laminated to cause the magnetization of return pole64adjacent surface70to be oriented in a direction substantially parallel to surface70. Preferably, the magnetization direction is less than a 4° departure from parallel, and more preferably, less than a 2° departure. Laminated portion74preferably extends from surface70of writer60toward back yoke66, but not as far as back yoke66. This configuration better ensures magnetic flux will travel along return pole64from back yoke66toward surface70.

Laminated portion74is formed of magnetic layers76and78separated by non-magnetic layer80. Magnetic layers76and78are each preferably formed of a magnetic material such as CoFe, CoNiFe, FeCoN, CoNiFeN, FeAlN, FeTaN, FeN, NiFe, NiFeCr, NiFeN, CoZr, CoZrNb, CoZrTa or other suitable material. Magnetic layers76and78are magnetically coupled to one another (either magnetostatically or antiferromagnetically) with magnetization82of magnetic layer76being substantially antiparallel to magnetization84of magnetic layer78. Shape anisotropy is used to ensure that magnetizations82and84remain substantially parallel to surface70of writer60, as opposed to substantially normal to surface70. In particular, magnetic layers76and78each have a width (its dimension into the page ofFIG. 3) substantially greater than its height (its dimension extending from surface70toward back yoke66), which results in an easy axis of magnetic layers76and78aligned in the direction of the layer's width. Further, the coupling strength between magnetic layers76and78is preferably sufficiently strong to resist rotation of magnetizations76and78from substantially parallel to surface70during a write operation for a magnetic field up to 1000 Oe.

Nonmagnetic layer80may be formed of any nonmagnetic material that is mechanically and chemically compatible with the magnetic materials used for magnetic layers76and78. Nonmagnetic layer80may be formed of either an electrically conducting or an electrically insulating material and may result in either magnetostatic or antiferromagnetic coupling between magnetic layers76and78. Suitable materials for nonmagnetic layer80include copper, ruthenium, gold, tantalum, aluminum, rhodium, chromium, copper-silver alloys, nitride, carbide, and various oxides, including aluminum oxide and silicon dioxide. The strength of the coupling between magnetic layers76and78can be controlled by a thickness of nonmagnetic layer80.

Thus, laminated portion74of return pole64reduces the concentration of magnetic flux along the edges of return pole64, and correspondingly minimizes any side track erasure caused by return pole64. Laminated portion74of return pole64further reduces eddy currents in return pole64, thus minimizing the eddy current skin effect at high recording frequencies. In sum, laminated portion74will cause the magnetic flux flow in return pole64to become more dispersed and uniform in the vicinity of surface70.

Although shown inFIG. 1as having only two magnetic layers separated by a single nonmagnetic layer, a perpendicular writer in accord with the present invention may incorporate any number of laminations in the return pole of the writer. However, it is preferred that the number of magnetic layers be an even number. The laminations may extend to any location between the back yoke of the writer and a surface opposite the back yoke.

FIG. 2introduces a more generalized embodiment of the present invention. More specifically,FIG. 2is a cross-sectional view of perpendicular writer90in accord with a second embodiment of the present invention. For ease of reference, elements common to both perpendicular writers60and90are numbered identically. Writer90is substantially similar to writer60ofFIG. 1, but substitutes laminated portion92for laminated portion74.

Laminated portion92of return pole64is formed of n magnetic layers94having (n−1) nonmagnetic layers96interspersed therebetween. Perpendicular writer60ofFIG. 2includes four magnetic layers94and three nonmagnetic layers96. Variable n may be any positive integer, but preferably is an even integer. These laminations cause the magnetization of return pole64adjacent surface70to be oriented in a direction substantially parallel (i.e., less than about 4° departure from parallel) to surface70. Preferably, this orientation of the magnetization will be less than 4° from parallel with surface, and more preferably, less than 2° from parallel. Laminated portion92preferably extends from surface70of writer60toward back yoke66, but not as far as back yoke66. This configuration better ensures magnetic flux will travel along return pole64from back yoke66toward surface70.

Magnetic layers94are magnetically coupled to one another (either magnetostatically or antiferromagnetically) with adjacent magnetic layers94having their magnetizations oriented substantially antiparallel to each other. Shape anisotropy is used to ensure that the magnetizations of magnetic layers94remain substantially parallel to surface70of writer90, as opposed to substantially normal to surface70. In particular, magnetic layers94each have a width (its dimension into the page ofFIG. 2) substantially greater than its height (its dimension extending from surface70toward back yoke66), which results in an easy axis of magnetic layers94falling in the direction of the layer's width. Further, the coupling strength between magnetic layers94is preferably sufficiently strong to resist rotation of the magnetization of magnetic layers94from substantially parallel to surface70during a write operation for a magnetic field up to 1000 Oe.

Nonmagnetic layers96may be formed of any nonmagnetic material that is mechanically and chemically compatible with the magnetic materials used for magnetic layers94. Nonmagnetic layers96may be formed of either an electrically conducting or an electrically insulating material and may result in either magnetostatic coupling, antiferromagnetic coupling, or a combination thereof between magnetic layers94. Suitable materials for nonmagnetic layers96include copper, ruthenium, gold, tantalum, aluminum, rhodium, chromium, copper-silver alloys, nitride, carbide, and various oxides, including aluminum oxide and silicon dioxide. The strength of the coupling between magnetic layers94can be controlled by thicknesses of nonmagnetic layers96.

Performance of perpendicular writer90is further improved by laminating portion98of main pole tip68. Laminated portion98includes m magnetic layers100and (m−1) nonmagnetic layers102interspersed therebetween. Perpendicular writer90illustrated inFIG. 2includes two magnetic layers100separated by a single nonmagnetic layer102. Although variable m may be any positive integer, variable m is preferably an even integer.

The present invention also applies to other configurations of perpendicular writers, such as a cusp-pole configuration as illustrated inFIG. 3. Specifically,FIG. 3is a cross-sectional view of perpendicular writer140in accord with a third embodiment of the present invention which includes main pole142, first return pole144, first back yoke146, second return pole148, and second back yoke150. Main pole142further includes main pole tip152adjacent main pole yoke154with main pole tip152preferably extending from main pole yoke154toward surface158of writer140and main pole yoke154being recessed a distance from surface158. Main pole142is separated from first and second return poles144and148at surface158by first and second write gaps, respectively, and is connected to first and second return poles144and148distal to surface158by first and second back yokes146and150, respectively. To write data to a magnetic medium, an electric current is caused to flow through a conductive coil (not shown) wrapped about main pole142, which in turn produces a magnetic field in main pole142, first and second return poles144and148, and first and second back yokes146and150.

Portions160and162of respective first and second return poles144and148respectively are laminated to cause the magnetizations of first and second return poles144and148adjacent surface158to be oriented in a direction substantially parallel to surface158. Preferably, the magnetization direction is less than a 4° departure from parallel, and more preferably, less than a 2° departure. Laminated portions160and162preferably extend from surface158of writer140toward first and second back yokes146and150, but not as far as first and second back yokes146and150.

Laminated portion160of first return pole144is formed of n magnetic layers164separated by (n−1) non-magnetic layers166interspersed therebetween. Likewise, laminated portion162of second return pole148is formed of m magnetic layers168separated by (m−1) nonmagnetic layers170interspersed therebetween. In the embodiment illustrated inFIG. 5, n and m both equal four; however, in other embodiments, these variables may differ from one another. Preferably, variables n and m are both even numbers. Magnetic layers164are each preferably formed of a magnetic material such as CoFe, CoNiFe, FeCoN, CoNiFeN, FeAlN, FeTaN, FeN, NiFe, NiFeCr, NiFeN, CoZr, CoZrNb, CoZrTa or other suitable material. Magnetic layers164are magnetically coupled to one another (either magnetostatically or antiferromagnetically) with adjacent magnetic layers164having their magnetizations oriented substantially antiparallel to each other. Shape anisotropy is used to ensure that the magnetizations of magnetic layers164remain substantially parallel to surface158of writer140, as opposed to substantially normal to surface158. In particular, magnetic layers164each have a width (its dimension into the page ofFIG. 3) substantially greater than its height (its dimension extending from surface158toward first back yoke146), which results in an easy axis of each magnetic layer164falling in the direction of the layer's width. Further, the coupling strength between magnetic layers164is preferably sufficiently strong to resist rotation of the magnetization of magnetic layers164from substantially parallel to surface during a write operation for a magnetic field up to 1000 Oe.

Nonmagnetic layers166may be formed of any nonmagnetic material that is mechanically and chemically compatible with the magnetic materials used for magnetic layers164. Nonmagnetic layers166may be formed of either an electrically conducting or an electrically insulating material and may result in magnetostatic coupling, antiferromagnetic exchange coupling, or a combination thereof between magnetic layers164. Suitable materials for nonmagnetic layers166include copper, ruthenium, gold, tantalum, aluminum, rhodium, chromium, copper-silver alloys, nitride, carbide, and various oxides, including aluminum oxide and silicon dioxide. The strength of the coupling between magnetic layers164can be controlled by thicknesses of nonmagnetic layers166. Laminated portion162of second return pole148is substantially similar to laminated portion160of first return pole144, and thus will not be discussed further here.

Like with perpendicular writer90ofFIG. 2, performance of perpendicular writer140is further improved by laminating portion172of main pole tip152. Laminated portion172includes p magnetic layers174and (p−1) nonmagnetic layers176interspersed therebetween. Preferably, variable p is a positive integer. Perpendicular writer140illustrated inFIG. 3includes two magnetic layers100separated by a single nonmagnetic layer102.

FIG. 4is a cross-sectional view of perpendicular writer180in accord with the present invention. Perpendicular writer180includes the addition of layers182and184on opposing sides of return pole64. Perpendicular writer180is essentially identical to perpendicular writer90ofFIG. 2, with the addition of layers182and184to the edges of laminated portion92of return pole64. Accordingly, elements common to both perpendicular writers90and180are numbered identically.

In accord with a fourth embodiment of the present invention, layers182and184are each formed of a low magnetic moment material. In this embodiment, layers182and184will reduce a magnetization gradient (i.e., magnetic charge) along the edges of return pole64adjacent surface70. This in turn helps to further suppress any side track erasure that may otherwise be caused by return pole64.

In accord with a fifth embodiment, layers182and184are formed of an antiferromagnetic material such as IrMn, PtMn, NiMn, NiO, FeMn, and alloys thereof, which alloys may further include materials such as Cr, B, or V. In this embodiment, layers182and184have their magnetization set in a direction substantially parallel to surface70. As such, they exert a pinning forcing on magnetic layers94, further ensuring that the magnetizations of magnetic layers94remain substantially parallel to surface70.

In a sixth embodiment, layers182and184are each formed of an antiferromagnetic material while return pole64is unlaminated. The antiferromagnetic material may include such as IrMn, PtMn, NiMn, NiO, FeMn, and alloys thereof, which alloys may further include materials such as Cr, B, or V. In this embodiment, layers182and184have their magnetization set in a direction substantially parallel to surface70. As such, they exert a magnetic force on unlaminated return pole64, which reduces the vertical magnetization component along the edges of return pole64.

FIG. 5is a cross-sectional view of perpendicular writer190in accord with the present invention. Elements common to both perpendicular writers90and180are numbered identically. In accord with a seventh embodiment of the present invention, perpendicular writer190adds hard ferromagnetic layers192and194and thin spacer layers196and198to the edges of laminated portion92of return pole64of perpendicular writer90ofFIG. 2. Hard ferromagnetic layers192and194may be formed of any hard ferromagnetic material (for instance, CoCrPt having a coercivity in a range of about 3000 Oe to about 5000 Oe). Hard ferromagnetic layers192and194are positioned on opposing sides of laminated portion92of return pole64, while spacer layers196and198are positioned between a respective one of hard ferromagnetic layers192and194and return pole64. Hard ferromagnetic layers192and194have their magnetizations set in a direction substantially parallel to surface70. As such, they exert a magnetic force on laminated portion92of return pole64, which further ensures that the magnetizations of magnetic layers94remain substantially parallel to surface70.

Alternately, in an eighth embodiment, return pole64may be unlaminated. Here, hard ferromagnetic layers192and194again have their magnetization set in a direction substantially parallel to surface70. As such, they exert a magnetic force on unlaminated return pole64, which reduces the vertical magnetization component along the edges of return pole64.

FIG. 6is a cross-sectional view of perpendicular writer200in accord with a ninth embodiment of the present invention. Writer200has a yoke-return pole configuration and includes main pole202, return pole204, and back yoke206. Main pole202further includes main pole tip208positioned adjacent main pole yoke210, with main pole tip208extending to surface212of writer200and main pole yoke210preferably recessed a distance from surface212. Alternate embodiments omit main pole yoke210. Main pole202is separated from return pole204at surface212by a write gap and is connected to return pole204distal to surface212by back yoke206. To write data to a magnetic medium, an electric current is caused to flow through a conductive coil (not shown) wrapped about back yoke206or main pole yoke210, which in turn produces a magnetic field in main pole202, return pole204, and back yoke206.

To further improve the performance of perpendicular writer200, at least a portion of return pole extension218nearest the write gap may be laminated with alternating layers of magnetic and nonmagnetic layers. As shown inFIG. 6, return pole extension218includes magnetic layers220and nonmagnetic layers222interspersed therebetween. Magnetic layers220and nonmagnetic layers222have properties as described above with reference to the laminated layers in earlier figures.

FIG. 7is a cross-sectional view of perpendicular writer230in accord with a tenth embodiment of the present invention. Writer230has a cusp-pole configuration and includes main pole232, first return pole234, first back yoke236, second return pole238, and second back yoke240. Main pole232further includes main pole tip242positioned between first and second main pole yokes244and246, with main pole tip242extending to surface248of writer230and first and second main pole yokes244and246preferably being recessed a distance from surface248. Alternate embodiments omit first and second main pole yokes244and246. Main pole232is separated from first and second return poles234and238at surface248by first and second write gaps, respectively, and is connected to first and second return poles234and238distal to surface248by first and second back yokes236and240, respectively. To write data to a magnetic medium, an electric current is caused to flow through a conductive coil (not shown) wrapped about main pole232, which in turn produces a magnetic field in main pole232, first and second return poles234and238, and first and second back yokes236and240.

First return pole234further includes first return pole body250and first return pole extension252. Likewise, second return pole238includes second return pole body254and second return pole extension256. First and second return pole extensions252and256are each a thin layer extending along surface248from a respective one of first and second return pole bodies250and254. Preferably, each of first and second return pole extensions252and256has a thickness D (measured in a direction substantially normal to surface248) less than about 0.3 micrometers, and more preferably, less than about 0.2 micrometers. The thinness of first and second return pole extensions252and256create a shape anisotropy that encourages the magnetization thereof to orient in a direction substantially parallel to surface248. Preferably, the magnetization direction is less than a 4° departure from parallel, and more preferably, is less than a 2° departure. First and second thin return pole extensions252and256thus causes a drastic reduction in the vertical magnetization component along the edges of first and second return poles234and238, and thus helps to suppress any side track erasure that otherwise might be caused by conventional return poles.

To further improve the performance of perpendicular writer230, at least a portion of each of first and second return pole extensions252and256may be laminated with alternating layers of magnetic and nonmagnetic layers. As shown inFIG. 7, first return pole extension252includes magnetic layers258and nonmagnetic layers260interspersed therebetween, while second return pole extension256includes magnetic layers262and nonmagnetic layers264interspersed therebetween. Magnetic layers258and262and nonmagnetic layers260and264have properties as described above with reference to the laminated layers in earlier figures.

FIG. 8is a cross-sectional view of perpendicular writer270in accord with an eleventh embodiment of the present invention. Writer270is substantially similar to writer230ofFIG. 7except that second return pole of238of writer270includes only second return pole body254and not second return pole extension256. Like previous embodiments, second return pole body254may be laminated adjacent surface248.

In sum, the present invention recognizes that magnetic flux in a return pole of a conventional perpendicular writer is concentrated along the edges of the return pole, and that this heavy concentration may cause undesired side track erasure by the return pole. To overcome this problem with conventional perpendicular writers, the present invention introduces a perpendicular writer having its return pole configured such that, during a write operation, the magnetization of the return pole adjacent a surface opposite a back via is substantially parallel to the adjacent surface of the writer. This reorientation of the magnetization of the return pole suppresses any side writing by the return pole.

In accord with the present invention, the magnetization of the return pole may be oriented in any of a number of ways, including the lamination of a portion of the return pole, the addition of materials adjacent the return pole to influence the magnetization of the return pole, and/or the addition of a thin return pole extension.

While many of the layers of the perpendicular writers illustrated inFIGS. 1-8are planar layers, it is contemplated that they may follow other contours. Additionally, none of the figures is rendered to scale.