Abstract:
The present invention provides a spin-valve magnetoresistive sensor comprising at least two ferromagnetic layers including a first and a second ferromagnetic layers. A first antiferromagnetic layer is layered adjacent to the first ferromagnetic layer for increasing the coercive force of the first ferromagnetic layer to pin the magnetization direction of the first ferromagnetic layer. A pair of second antiferromagnetic layers are respectively positioned adjacent to the longitudinal ends of the second ferromagnetic layer. Further, a pair of third ferromagnetic layers are respectively layered adjacent to said pair of second antiferromagnetic layers for inducing magnetic anisotropy to pin the magnetization direction of each third ferromagnetic layer in a direction perpendicular to the pinned magnetization direction of the first ferromagnetic layer, thereby imposing a longitudinal bias on the second ferromagnetic layer to stabilize magnetic domains therein in order to suppress Barkhausen noise. The magnetization direction of the second ferromagnetic layer remains free to rotate in accordance with the direction of an external magnetic field, thereby changing the electrical resistance of the sensor.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sensor comprising a magnetoresistive element and used as a magnetic head, a potentiosensor, an angular sensor, and the like, a manufacturing method thereof and a magnetic head comprising the sensor. 
     2. Description of the Related Art 
     As magnetoresistive reading heads (MR heads), AMR (Anisotropic Magnetoresistive) heads using the anisotropic magnetoresistive effect, and GMR (Giant Magnetoresistive) heads using spin dependent scattering are conventionally known. An example of the GMR heads is the spin-valve head disclosed in U.S. Pat. No. 5,159,513 in which high magnetoresistance is exhibited in a low magnetic field. 
     FIGS. 10 and 11 are drawings respectively showing the schematic constructions of AMR head element structures. 
     The head element shown in FIG. 10 comprises an insulation layer  2  and a ferromagnetic layer (AMR material layer)  3  which are laminated on a soft magnetic layer  1 , antiferromagnetic layers  4  which are laminated on both ends of the ferromagnetic layer  3  with a space therebetween that is substantially equal to a track width, and electrically conductive layers  5  respectively laminated on the antiferromagnetic layers  4 . The head element shown in FIG. 11 comprises a soft magnetic layer  1 , an insulation layer  2  and a ferromagnetic layer  3  which form a laminate, hard magnetic layers  6  provided on both sides of the laminate to hold it therebetween, and electrically conductive layers  5  respectively provided on the hard magnetic layers  6 . 
     For optimum operation of such AMR heads, two magnetic bias fields are required for the ferromagnetic layer  3  exhibiting the AMR effect. 
     A first magnetic bias field functions to make the resistance of the ferromagnetic layer  3  change in linear response to a magnetic flux from a magnetic recording medium. The first magnetic bias field is perpendicular (in the Z direction shown in FIG. 1) to the surface of the magnetic recording medium and parallel to the film surface of the ferromagnetic layer  3 . The first magnetic bias field is generally referred to as a “lateral bias” and can be obtained by flowing a sensing current through the ARM head element from the electrically conductive layers  5 . 
     A second magnetic bias field is generally referred to as a “longitudinal bias” and applied in parallel (in the X direction shown in FIG. 1) with the film surface of the ferromagnetic layer  3 . The longitudinal magnetic bias field is applied for suppressing the Barkhausen noise generated due to the formation of many magnetic domains in the ferromagnetic layer  3 , i.e., causing the resistance to smoothly change with the magnetic flux from the magnetic recording medium with less noise. 
     However, in order to suppress the Barkhousen noise, it is necessary to put the ferromagnetic layer into a single magnetic domain state. As a method of applying the longitudinal bias for this purpose, the following two methods are generally known. A first method uses the head element structure shown in FIG. 11 in which the hard magnetic layers  6  are disposed on both sides of the ferromagnetic layer  3  to employ a leakage magnetic flux from the hard magnetic layers  6 . A second method uses the head element structure shown in FIG. 10 in which the exchange anisotropic magnetic field developed in the contact boundary surfaces between the antiferromagnetic layers  4  and the ferromagnetic layer  3  is employed. 
     As an element structure which employs exchange anisotropic coupling due to the antiferromagnetic layers, the exchange bias structure shown in FIG. 12, and the spin-valve structure shown in FIG. 13 are known. 
     The structure shown in FIG. 12 is classified as the structure shown in FIG. 10, and comprises a ferromagnetic layer  22 , a non-magnetic layer  23  and a ferromagnetic layer  24  exhibiting the magnetoresistive effect which are laminated on a lower insulation layer  21 , antiferromagnetic layers  25  and lead layers  26  which are provided on both sides of the ferromagnetic layer  24  with a space substantially equal to the track width TW, and an upper insulation layer  27  provided on these layers. 
     In the structure shown in FIG. 12, a longitudinal bias is applied to the ferromagnetic layer  24  due to the exchange anisotropic coupling in the boundaries between the ferromagnetic layer  24  and the antiferromagnetic layers  25  to put regions B (the regions where the ferromagnetic layer  24  contacts the antiferromagnetic layers  25 ) shown in FIG. 12 into a single magnetic domain state in the X direction. This brings region A of the ferromagnetic layer  24  within the track width into a single magnetic domain state in the X direction. A sensing current is supplied to the ferromagnetic layer  24  from the lead layers  26  through the antiferromagnetic layers  25 . When the sensing current is supplied to the ferromagnetic layer  24 , a lateral magnetic bias field in the Z direction is applied to the ferromagnetic layer  24  due to the magnetostatic coupling energy from the ferromagnetic layer  22 . In this way, when the leakage magnetic field is applied to the ferromagnetic layer  24  magnetized by the longitudinal magnetic bias field and the lateral magnetic bias field from the magnetic recording medium, the electric resistance to the sensing current linearly responds to the magnitude of the leakage magnetic field and changes in proportion thereto. Therefore, the leakage magnetic field can be sensed by a change in the electric resistance. 
     The structure shown in FIG. 13 comprises a free ferromagnetic layer  28 , a non-magnetic electrically conductive layer  29  and a ferromagnetic layer  24  which are laminated to form a magnetoresistive element  19 , and an antiferromagnetic layer  25  and an upper insulation layer  27  which are laminated in turn on the ferromagnetic layer  24 . 
     In the structure shown in FIG. 13, the sensing current is supplied to the magnetoresistive element  19 . The magnetization of the ferromagnetic layer  24  is fixed in the Z direction due to exchange anisotropic coupling with the antiferromagnetic layer  25 . Therefore, when a leakage magnetic field is applied from a magnetic recording medium which is moved in the Y direction, the electric resistance of the magnetoresistive element  19  changes with a change in the magnetization direction of the free ferromagnetic layer  28 , and the leakage magnetic field can thus be sensed by this change in the electric resistance. 
     Other known structures for optimum operation of the above structures by employing the spin valve structure include the structure shown in FIG. 14 which comprises a free ferromagnetic layer  7 , a non-magnetic buffer layer  8 , a pinned ferromagnetic layer  9  and an antiferromagnetic layer  10 , which are laminated in turn to form a laminate, hard magnetic layers  11  which are provided on both sides of the laminate, and electrically conductive layers  12  respectively provided on the hard magnetic layers  11 , and the structure shown in FIG. 15 which comprises a free ferromagnetic layer  7 , a non-magnetic buffer layer  8 , a pinned ferromagnetic layer  9  and an antiferromagnetic layer  10 , which are laminated in turn to form a laminate, an electrically conductive layer  12  and an antiferromagnetic layer  13  which are provided on the upper and lower sides of the laminate to hold it therebetween at either side thereof, and a buffer layer  14  provided adjacent to the whole laminate. 
     In the structure shown in FIG. 14, it is necessary that the magnetization direction of the free ferromagnetic layer  7  is directed in the track direction (the X direction shown in FIG. 14) in the state where a bias in the track direction is applied to the free ferromagnetic layer  7  to put it into a single magnetic domain state by the hard magnetic layers  11 , and that the magnetization direction of the pinned ferromagnetic layer  9  is directed in the Z direction shown in FIG. 14, i.e., the direction perpendicular to the magnetization direction of the free ferromagnetic layer  7 , in the state where a bias is applied in the Z direction to put the pinned ferromagnetic layer  9  into a single magnetic domain state. In other words, the magnetization direction of the pinned ferromagnetic layer  9  must not be changed by a magnetic flux (in the Z direction shown in FIG. 14) from the recording magnetic medium, and the magnetization direction of the free ferromagnetic layer  7  is changed within the range of 90±θ with the magnetization direction of the pinned ferromagnetic layer  9  to obtain linear response of magnetoresistance. 
     In order to fix the magnetization direction of the pinned ferromagnetic layer  9  in the Z direction shown in FIGS. 14 and 15, a relatively large bias magnetic field is required, and this bias magnetic field is preferably as large as possible. In order to overcome an antiferromagnetic field in the Z direction shown in FIGS. 14 and 15, and avoid fluctuation of the magnetization direction due to the magnetic flux from the recording magnetic medium, a bias magnetic field of at least 100 Oe is required. 
     In the structures shown in FIGS. 14 and 15, this bias magnetic field is obtained by using the exchange anisotropic coupling produced by providing the pinned ferromagnetic layer  9  and the antiferromagnetic layer  10  in contact with each other. 
     The bias applied to the free ferromagnetic layer  7  is adapted for securing linear response and suppressing the Barkhausen noise generated due to the formation of many magnetic domains. Like the longitudinal bias in an AMR head, the structure shown in FIG. 14 uses as the bias the leakage magnetic flux from the hard magnetic layers  11  which are provided on both sides of the free ferromagnetic layer  7 . The structure shown in FIG. 15 uses as the bias the exchange anisotropic magnetic field produced in the contact boundary surfaces between the free ferromagnetic layer  7  and the antiferromagnetic layers  13  provided on both sides of the free ferromagnetic layer  7 . 
     As described above, the exchange anisotropic magnetic field produced in the contact boundary with the antiferromagnetic layers is used as the longitudinal bias in the AMR head, the bias for the pinned ferromagnetic layer in a spin valve head, and the bias for the free ferromagnetic layer. As result, a magnetoresistive head exhibiting good linear response and the effect of suppressing Barkhousen noise is realized. 
     The exchange anisotropic magnetic field is the phenomenon caused by an exchange interaction between the magnetizing moments of the ferromagnetic layer and the antiferromagnetic layer in the contact boundary layer therebetween. As the antiferromagnetic layer producing the exchange anisotropic magnetic field with the ferromagnetic layer, e.g., an NiFe layer, an FeMn layer is well known. However, the FeMn layer has a problem in that since it has low corrosion resistance, corrosion proceeds in the process of manufacturing a magnetic head and in operation of the magnetic head, thereby deteriorating the exchange anisotropic magnetic field, and damaging the recording magnetic medium in some cases. It is known that the temperature in the vicinity of the FeMn layer during operation of the magnetic head readily increases to about 120° C. by heat of the stationary sensing current. However, the exchange anisotropic magnetic field produced by the FeMn layer is extremely sensitive to a temperature change, and substantially linearly decreases with a temperature increase to about 150° C. at which it disappears (blocking temperature: Tb). There is also a problem in that a stable exchange anisotropic magnetic field cannot be obtained. 
     On the other hand, as an invention of improvements in the corrosion resistance and blocking temperature of an FeMn film, for example, the NiMn alloy or NiMnCr alloy having a face-centered tetragonal structure disclosed in U.S. Pat. Nos. 5,315,468 and 5,436,778 is known. However, the corrosion resistance of an Nimn layer is higher than that of the FeMn layer, but is insufficient for practical use. An NiMnCr layer contains Cr which is added for improving the corrosion resistance of the NiMn layer, but has a problem in that although the corrosion resistance is improved by adding Cr, the magnitude of the exchange anisotropic magnetic field and the blocking temperature are decreased. 
     Further, in order to obtain the exchange anisotropic magnetic field in the NiMn alloy or NiMnCr alloy, it is necessary to form a CuAg-I type ordered structure crystal having the face-centered tetragonal (fct) structure in a portion of the antiferromagnetic layer, and it is, of course, necessary to control ordered-disordered transformation and the volume ratio of ordered phase and disordered phase. Therefore, there is a problem in that in order to obtain stable properties, control and management of the process for manufacturing a magnetic head must be significantly complicated. There are also problems in that in order to obtain the necessary exchange anisotropic magnetic field, heat treatment in a magnetic field must be repeated several times, and in that the temperature must be decreased at a low rate, for example, a time required for decreasing the temperature from 255° C. to 45° C. is 17 hours (refer to Appl. Phys. Lett., 65(9), Aug. 29, 1994). Thus the treatment time in the manufacturing process is increased, and the efficiency of manufacture deteriorates. 
     As an invention of improvement in the blocking temperature of the FeMn layer, a method is disclosed in U.S. Pat. No. 4,809,109 in which a NiFe/FeMn laminated film is heat-treated at a temperature of 260 to 350° C. for 20 to 50 hours to form a Ni—Fe—Mn three-element alloy layer in the NiFe/FeMn boundary surface due to diffusion by heat treatment. However, it can be understood that this method has no effect on improvement in corrosion resistance which is the greatest problem, and this method has a problem in that the required heat treatment time is as long as 20 to 50 hours, and thus deteriorates the efficiency of manufacture. 
     On the other hand, Mn system alloys such as NiMn, PtMn, AuMn, RhMn 3  and the like are shown as antiferromagnetic materials in an existing publication, e.g., “Magnetic Material Handbook” issued by Asakura Shoten. However, there is no comment about an exchange anisotropic magnetic field in the contact boundary surface with the ferromagnetic layer, and characteristics of an antiferromagnetic layer itself and exchange anisotropic magnetic field in a super thin film having a thickness of several hundreds Å are not entirely clear. 
     In the element structure shown in FIG. 14, the free ferromagnetic layer  7  to which the bias is applied by the right and left hard magnetic layers  11  tends to become an insensitive region where the magnetization direction in the track end portions (the region denoted by reference numeral  16  in FIG. 14) near the hard magnetic layers  11  is hardly changed. Therefore, when the track width is decreased with improvement in the recording density of the recording magnetic medium, this structure possible causes a problem. 
     The element structure using an exchange coupling bias shown in FIG. 15 can thus become promising, but the structure has the problem below when a longitudinal bias is applied to the spin valve element structure by the exchange coupling bias method. 
     In the spin valve element structure shown in FIG. 15, rotation of magnetization of the pinned ferromagnetic layer  9  is fixed by the antiferromagnetic layer  10 . while the magnetization direction of the track end portions of the free ferromagnetic layer  7  is fixed for the longitudinal bias by the antiferromagnetic layers  13 . A difference between the magnetization directions in which the antiferromagnetic layer  10  and the antiferromagnetic layers  13  are respectively fixed is an angle of 90°. 
     The magnetization direction of each of the magnetic layers is generally controlled by deposition in a magnetic field or annealing in a magnetic field after deposition. However, it is very difficult to control the magnetization direction of the antiferromagnetic layer  10  which is deposited after the antiferromagnetic layers  13  are deposited, without disturbing the magnetization direction of the antiferromagnetic layers  13 . 
     Also a technique is disclosed in U.S. Pat. No. 5,528,440 in which the above problems are solved by using magnetic films having different Neel temperatures and employing different heat treatment temperatures for the respective magnetic films. However, this technique also has the need for using an FeMn alloy having a low Neel temperature, and thus has a problem in that the drawback of low corrosion resistance and the drawback of sensitivity to a temperature change due to the blocking temperature cannot be solved. 
     SUMMARY OF THE INVENTION 
     The present invention has been achieved in consideration of the above situation, and an object of the invention is to provide a magnetoresistive sensor with excellent corrosion resistance and linear response in which a necessary sufficient exchange anisotropic magnetic field can be applied in a thin film, and Barkhousen noise is suppressed. 
     Another object of the present invention is to provide a magnetoresistive sensor in which by providing an antiferromagnetic layer having a high blocking temperature, the linear response and resistance to temperature changes are improved and Barkhousen noise is suppressed. 
     A further object of the present invention is to provide a method of manufacturing a magnetoresistive sensor having the above excellent properties, which has no need for heat treatment in a magnetic field for a long time using special heat treatment equipment, which can manufacture the sensor by usual heat treatment, and which can reduce the heat treatment time, as compared with a conventional method. 
     In order to achieve the objects of the present invention, there is provided a magnetoresistive sensor comprising at least two ferromagnetic layers provided with a non-magnetic layer therebetween; a coercive force increasing layer comprising a first antiferromagnetic layer provided adjacent to one of the ferromagnetic layers, for increasing the coercive force of that ferromagnetic layer to pin magnetization reversal thereof, the other ferromagnetic layer having freed magnetization reversal; and a second antiferromagnetic layer comprising an antiferromagnetic material provided adjacent to the other ferromagnetic layer having freed magnetization reversal, for applying a longitudinal bias to the other ferromagnetic layer to induce unidirectional magnetic anisotropy to stabilize a magnetic domain. 
     In the present invention, the magnetization direction of the ferromagnetic layer having pinned magnetization reversal is preferably substantially perpendicular to the magnetization direction of the ferromagnetic layer having free magnetization without an external magnetic field. 
     In the present invention, the coercive force increasing layer comprises α-Fe 2 O 3 , and the coercive force of the ferromagnetic layer having magnetization reversal pinned by the coercive force increasing layer is preferably higher than the unidirectional exchange bias magnetic field simultaneously induced in the ferromagnetic layer by α-Fe 2 O 3 . 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing a magnetoresistive sensor in accordance with a first embodiment of the present invention; 
     FIG. 2 is a drawing showing the magnetization direction of each of the ferromagnetic layers in the sensor shown in FIG. 1; 
     FIG. 3 is a sectional view showing a magnetoresistive sensor in accordance with a second embodiment of the present invention; 
     FIG. 4 is a perspective view showing a thin film magnetic head comprising a magnetoresistive sensor of the present invention; 
     FIG. 5 is a sectional view showing a principal portion of the thin film magnetic head shown in FIG. 4; 
     FIG. 6 is a perspective view showing the thin film magnetic head shown in FIG. 4, with a sectional portion; 
     FIG. 7 is a graph showing the curve of resistance change of an example sample; 
     FIG. 8 is a graph showing the blocking temperatures of magnetoresistive sensor samples using α-Fe 2 O 3 ; 
     FIG. 9A is a drawing showing the magnetizing curve of a pinned ferromagnetic layer, and 
     FIG. 9B is a drawing showing the magnetoresistance curve of a magnetoresistive sensor; 
     FIG. 10 is a sectional view showing a first example of conventional magnetoresistive sensors; 
     FIG. 11 is a sectional view showing a second example of conventional magnetoresistive sensors; 
     FIG. 12 is a sectional view showing a third example of conventional magnetoresistive sensors; 
     FIG. 13 is a sectional view showing a fourth example of conventional magnetoresistive sensors; 
     FIG. 14 is a sectional view showing a fifth example of conventional magnetoresistive sensors; and 
     FIG. 15 is a sectional view showing a sixth example of conventional magnetoresistive sensors. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In order to achieve the objects of the present invention, there is provided a magnetoresistive sensor comprising at least two ferromagnetic layers provided with a non-magnetic layer therebetween; a coercive force increasing layer comprising a first antiferromagnetic layer provided adjacent to one of the ferromagnetic layers, for increasing the coercive force of that ferromagnetic layer to pin magnetization reversal thereof, the other ferromagnetic layer having free magnetization reversal; and a second antiferromagnetic layer comprising an antiferromagnetic material provided adjacent to the other ferromagnetic layer having free magnetization reversal, for applying a longitudinal bias to the other ferromagnetic layer to induce unidirectional magnetic anisotropy to stabilize a magnetic domain. 
     In the present invention, the magnetization direction of the ferromagnetic layer having pinned magnetization reversal is preferably substantially perpendicular to the magnetization direction of the ferromagnetic layer having free magnetization without an external magnetic field. 
     In the present invention, the coercive force increasing layer comprises α-Fe 2 O 3 , and the coercive force of the ferromagnetic layer having magnetization reversal pinned by the coercive force increasing layer is preferably higher than the unidirectional exchange bias magnetic field simultaneously induced in the ferromagnetic layer by α-Fe 2 O 3 . 
     In the present invention, the second antiferromagnetic layer for applying the longitudinal bias is preferably provided on either end side of the magnetic sensing region of the other ferromagnetic layer having free magnetization reversal with a space, which equals to the predetermined track width corresponding to the width of the magnetic sensing region, so as to be adjacent to the other ferromagnetic layer. 
     In the present invention, the ferromagnetic layer having free magnetization reversal is formed in the magnetic sensing region within a width substantially equal to the track width, and a laminate of an antiferromagnetic layer and another ferromagnetic layer laminated on this antiferromagnetic layer is formed on either side of the other ferromagnetic layer having free magnetization reversal to apply the longitudinal bias to the other ferromagnetic layer. 
     Further, the ferromagnetic layer laminated on the second antiferromagnetic layer for applying the longitudinal bias preferably comprises an amorphous thin film. 
     The antiferromagnetic layer for applying the longitudinal bias preferably comprises an X—Mn alloy (wherein X indicates at least one of Pt, Pd, Ir, Ru and Rh) type alloy thin film. 
     The present invention further provides a magnetic head comprising the magnetoresistive sensor constructed as described above. 
     On the other hand, when manufacturing the magnetoresistive sensor in which the second antiferromagnetic layers for applying the longitudinal bias are provided on both end sides of the magnetic sensing region of the ferromagnetic layer having free magnetization reversal opposite to each other with a space therebetween, which equals to a predetermined track width corresponding to the width of the magnetic sensing region, so as to contact the ferromagnetic layer, preferred conditions are the following: 
     The unidirectional magnetic anisotropy induced in the ferromagnetic layer having free magnetization reversal which is provided adjacent to the second antiferromagnetic layer for applying the longitudinal bias is produced by forming the ferromagnetic layer while applying a magnetic field or effecting heat treatment in a magnetic field after the formation of the ferromagnetic layer; and 
     the magnetization direction of the ferromagnetic layer having pinned magnetization reversal which is provided adjacent to the coercive force increasing layer is determined in the permanent magnetization step after the step for determining the direction of the magnetic anisotropy of the ferromagnetic layer having free magnetization reversal. 
     When manufacturing the magnetoresistive sensor in which the ferromagnetic layer having free magnetization reversal is formed in the magnetic sensing region within a width substantially equal to the track width, and a laminate of the antiferromagnetic layer of an antiferromagnetic material and another ferromagnetic layer is formed on either side of the ferromagnetic layer to apply the longitudinal bias, preferred conditions are the following: 
     The unidirectional magnetic anisotropy induced in the ferromagnetic layer which is provided adjacent to the antiferromagnetic layer to form each laminate is produced by forming the ferromagnetic layer while applying a magnetic field or effecting heat treatment in a magnetic layer after formation of the ferromagnetic layer; and 
     the magnetization direction of the ferromagnetic layer having pinned magnetization reversal which is provided adjacent to the coercive force increasing layer is determined in the permanent magnetization step after the step for determining the direction of magnetic anisotropy of the ferromagnetic layer of each laminate. 
     An embodiment of the present invention will be described below with reference to the drawings. 
     FIG. 1 shows a magnetoresistive sensor in accordance with an embodiment of the present invention. The magnetoresistive sensor comprises a coercive force increasing layer  31 , a ferromagnetic layer  32 , a non-magnetic layer  33  and a ferromagnetic layer  34  which are laminated in turn on the coercive force increasing layer  31 , antiferromagnetic layers  35  laminated on both ends of the ferromagnetic layer  34  with a space therebetween substantially equal to the track width TW, lead layers  36  respectively laminated on the antiferromagnetic layers  35 , and an upper insulation layer  37  laminated to cover the lead layers  36  and the ferromagnetic layer  34 . In the structure of this embodiment, the coercive force increasing layer  31 , the ferromagnetic layer  32 , the non-magnetic layer  33  and the ferromagnetic layer  34  constitute a spin-valve magnetoresistive element  30 . 
     The coercive force increasing layer  31  acts magnetic exchange coupling force on the ferromagnetic layer  32  formed thereon to increase the coercive force of the ferromagnetic layer  32  and pin the magnetization direction thereof. The coercive force increasing layer  31  comprises α-Fe 2 O 3  having a high Neel temperature. 
     Each of the ferromagnetic layers  32  and  34  comprises a thin film of a ferromagnetic material, particularly, an Ni—Fe alloy, a Co—Fe alloy, an Ni—Co alloy, Co, an Ni—Fe—Co alloy or the like. Alternatively, the ferromagnetic layer  32  may comprise a Co layer, and the ferromagnetic layer  34  may comprise an Ni—Fe alloy layer or a laminated structure of a Co layer and an Ni—Fe alloy layer. In the case of a two-layer structure of a Co layer and an Ni—Fe alloy layer, a thin Co layer may be disposed on the non-magnetic layer side. 
     This is because in a giant magnetoresistive effect generating mechanism having a structure comprising the non-magnetic layer  33  held between the ferromagnetic layers  32  and  34 , the Co/Cu boundary surface has the large spin-dependent scattering effect of conduction electrons, and a structure comprising the ferromagnetic layers  32  and  34  made of the same material has the lower possibility of causing factors other than the spin-dependent scattering of conduction electrons and a higher magnetoresistive effect than a structure comprising the ferromagnetic layers made of different materials. For this reason, when the ferromagnetic layer  32  comprises Co, it is preferable that a Co layer having a predetermined thickness is provided on the non-magnetic layer side of the ferromagnetic layer  34 . Alternatively, the ferromagnetic layer  34  may have a concentration gradient layer in which the non-magnetic layer side of the ferromagnetic layer  34  is put into an alloy state containing much Co, and the Co concentration gradually decreases toward the upper protective layer side, without a Co layer separately provided. 
     The non-magnetic layer  33  comprises a non-magnetic material such as Cu, Cr, Au, Ag or the like, and is formed to a thickness of 20 to 40 Å. If the thickness of the non-magnetic layer  33  is less than 20 Å, magnetic coupling easily occurs between the ferromagnetic layers  32  and  34 . If the thickness of the non-magnetic layer  33  exceeds 40 Å, the ratio of conduction electrons which are scattered in the boundary surfaces between the non-magnetic layer  3  and the ferromagnetic layers  32  and  34  and which cause the magnetoresistive effect is decreased, thereby undesirably decreasing the magnetoresistive effect due to the shunt effect of a current. 
     The antiferromagnetic layers  35  preferably comprise an antiferromagnetic material different from the antiferromagnetic layer  31 , for example, an X—Mn alloy having a disordered structure. In this composition formula, X is preferably at least one of Ru, Rh, Ir, Pd and Pt. 
     The Mn system alloy has a disordered crystal structure which means a state other than ordered crystal structures such as the face-centered tetragonal structure (fct ordered lattice; CuAuI structure and the like). Namely, the Mn alloy used in the present invention is not subjected to heat treatment at high temperature for a long time for making it an ordered crystal structure (the CuAuI structure or the like) such as the face-centered tetragonal structure after a film of the Mn alloy is deposited by sputtering. The disordered crystal structure means a state where the film is formed by a deposition method such as sputtering without further treatment, or a state the deposited film is then annealed. 
     When X in the X—Mn alloy denotes a single metal atom, the X contents of Ru, Rh, Ir, Pd and Pt are preferably within the ranges of 10 to 45 atomic %, 10 to 40 atomic %, 10 to 40 atomic %. 10 to 25 atomic % and 10 to 25 atomic %, respectively. In these ranges, 10 to 45 atomic % means not less than 10 atomic % and not more than 45 atomic %, and the upper and lower limits of all numerical ranges indicated by “” are defined by “not less than” and “not more than”, respectively. 
     The antiferromagnetic layers  35  of the X—Mn type alloy having the disordered crystal structure are capable of applying the longitudinal bias to the ferromagnetic layer  34  due to unidirectional anisotropy, and pinning the rotation of magnetization at both ends of the ferromagnetic layer  34  which contacts the ferromagnetic layers  35 . 
     Also the antiferromagnetic layers  35  of the X—Mn system alloy have excellent corrosion resistance and less variation in the exchange anisotropic magnetic field (Hex) with a temperature change, as compared with conventional antiferromagnetic layers of Fe—Mn. Therefore, the use of the antiferromagnetic layers  35  improves environmental resistance, prevents the occurrence of noise in detection of the leakage magnetic field from a recording magnetic medium and enables high-quality magnetic detection. Since the antiferromagnetic layers  35  of the X—Mn alloy has no need for heat treatment at high temperature for a long time, it has the low possibility of producing element diffusion between the respective magnetic layers under heating, and causes no problem of change and deterioration in magnetic properties or breaking of the insulation layer. 
     The upper protective layer  37  is provided for setting the gap between the upper protective layer  37  and an upper shielding magnetic layer, and preventing oxidation of the ferromagnetic layer  34 . The upper protective layer  37  preferably comprises an insulating material such as Al 2 O 3 , quartz or the like. 
     By providing the antiferromagnetic layers  35  on the ferromagnetic layer  34 , a bias in the magnetization direction shown by an arrow a in FIG. 1 can be applied to the ferromagnetic layer  34  by imparting unidirectional anisotropy thereto to put the ferromagnetic layer  34  into a single magnetic domain state. The coercive force increasing layer  31  deposited over the entire surface of the ferromagnetic layer  32  can pin the magnetization direction of the ferromagnetic layer  32  to arrange the magnetization in the direction b perpendicular to the drawing of FIG.  1 . Therefore, the magnetization direction of the ferromagnetic layer  34  is directed in the direction of the arrow a shown in FIGS. 1 and 2, and the magnetization direction of the ferromagnetic layer  32  is directed in the direction of the arrow b so that both magnetization directions can be angled at about 90°. 
     In the structure shown in FIG. 1, a sensing current is supplied to the magnetoresistive element  30 . 
     In the structure shown in FIG. 1, the coercive force of the ferromagnetic layer  32  is increased by exchange magnetic coupling in the presence of the coercive force increasing layer  31  to pin the magnetization direction of the ferromagnetic layer  32 , and the magnetization direction of the other ferromagnetic layer  34  is freed in a region corresponding to the track width TW. As a result, a difference in coercive force occurs between the ferromagnetic layers  32  and  34 , thereby obtaining the giant magnetoresistive effect. Namely, when an external magnetic field such as the leakage magnetic field from the recording magnetic medium which is moved in the Y direction acts on the central region corresponding to the track width TW in the ferromagnetic layer  34  having free magnetization rotation, the magnetization direction of the ferromagnetic layer  34  is easily rotated, and the resistance of the magnetoresistive element  30  easily changes with the rotation. Therefore, magnetic information of the recording magnetic medium can be read by measuring the change in resistance. 
     Also, since at the time of the change in resistance, the ferromagnetic layer  34  is put into a single magnetic domain state, and the longitudinal bias is applied thereto, the change in resistance can be obtained with good linear response without causing Barkhousen noise. 
     In the structure shown in FIG. 1, since the coercive force increasing layer  31  comprises α-Fe 2 O 3 , which is an oxide and has excellent corrosion resistance and a high Neel temperature, as compared with FeMn, the structure has high resistance to a temperature change. 
     FIG. 3 shows a magnetoresistive sensor in accordance with another embodiment of the present invention. The magnetoresistive sensor of this embodiment comprises a coercive force increasing layer  41 , a pinned ferromagnetic layer  42 , a non-magnetic layer  43  and a free ferromagnetic layer  44 , which constitute a laminate  45  having a trapezoidal section; antiferromagnetic layers  46  provided on both sides of the laminate  45 ; a ferromagnetic layer  47  and an electrically conductive layer  48  which are laminated on each of the antiferromagnetic layers  46 . In this embodiment, the antiferromagnetic layers  46  are provided so that the ends thereof cover the sides of the antiferromagnetic layer  41 , the pinned ferromagnetic layer  42  and the non-magnetic layer  43 , and cover the sides of the free ferromagnetic layer  44  to about a half of the thickness thereof. The ferromagnetic layers  47  on the antiferromagnetic layers  46  are provided so that the ends thereof cover the sides of the free ferromagnetic layer  44  to about a half of the thickness thereof. The relation between the thicknesses of the respective layers is not limited to that shown in FIG.  1 . The positions of the antiferromagnetic layers  46  and the ferromagnetic layers  37  may be reversed, or many antiferromagnetic layer  46  and the ferromagnetic layer  47  may be alternately laminated. 
     In the above-mentioned structure, the coercive force increasing layer  41 , the pinned ferromagnetic layer  42 , the non-magnetic layer  43 , and the free ferromagnetic layer  44  comprise the same materials as the coercive force increasing layer  31 , the ferromagnetic layer  32 , the non-magnetic layer  33  and the ferromagnetic layer  34 , respectively, used in the first embodiment. The antiferromagnetic layers  46  preferably comprise the same material as the antiferromagnetic layers  35  used in the first embodiment, and the ferromagnetic layers  47  preferably comprise a ferromagnetic layer of an amorphous material such as CoNbZr, CoFeB, CoFeZr or the like, or a laminated film comprising one of these layers and a crystalline film of a NiFe alloy or the like. 
     In the structure shown in FIG. 3, the magnetization direction of the ferromagnetic layers  47  can be pinned in the direction of the arrow a shown in FIG. 3 by the unidirectional anisotropy of the antiferromagnetic layers  46 , and at the same time, the magnetization direction of the free ferromagnetic layer  44  can be directed to the same direction of the arrow a as the magnetization direction of the ferromagnetic layer  47 , to apply the longitudinal bias to the free ferromagnetic layer  44 . The magnetization direction of the pinned ferromagnetic layer  42  is pinned to the direction of the arrow b shown in FIG. 3 by the coercive force increasing layer  41 . 
     As described above, the free ferromagnetic layer  44  and the ferromagnetic layers  47  can be put into a single magnetic domain region, and the magnetization direction of the free ferromagnetic layer  44  can be made cross the magnetization direction of the pinned ferromagnetic layer  42  at a right angle. 
     When the ferromagnetic layers  47  comprise an amorphous ferromagnetic material, there is the advantage of introducing a sensor exhibiting less side reading (reading the magnetic field of the recording magnetic medium in a region other than the track region) and less dispersion in unidirectional anisotropy because the amorphous ferromagnetic layer has a little MR effect. 
     In the structure of this embodiment, since the free ferromagnetic layer  44  can be put into a single magnetic domain state to apply the longitudinal bias to the ferromagnetic layer  44 , a change in resistance can be obtained with good linear response without causing Barkhousen noise, as in the structure of the first embodiment. 
     FIGS. 4 to  6  shows an example of the structure of a thin film magnetic head having the element structure shown in FIG. 1 or  3 . 
     The magnetic head HA of this example is a floating type which is loaded on a hard disk drive or the like. In a slider  51  of this magnetic head HA, the side shown by (i) in FIG. 4 is the leading side on the upstream side in the direction of movement of the disk surface, and the side shown by (ii) in FIG. 4 is the trailing side. On the side of the slider  51  opposite to a disk are formed rail-shaped ABS surfaces  51   a  and  51   b,  and an air groove  51   c.    
     On the side  51   d  of the slider  51  on the trailing side is provided a thin film magnetic head  50 . 
     The thin film magnetic head  50  of this example is a combination magnetic head having the sectional structures shown in FIGS. 5 and 6, and comprises an MR head (reading head) h 1  and an inductive head (writing head) h 2 , which are laminated in turn on the side  51   d  of the slider  51  on the trailing side. 
     The MR head h 1 , of this example detects the leakage magnetic field from the recording magnetic medium such as a disk or the like by using the magnetoresistive effect to read a magnetic signal. As shown in FIG. 5, the MR head h 1  comprises a lower shielding layer  53  comprising a magnetic alloy such as sendust (Fe—Al—Si) and formed on the trailing side of the slider  51 , and a upper gap layer  54  formed on the lower gap layer  53  and comprising a non-magnetic material such as aluminum oxide (Al 2 O 3 ) or the like. On the upper gap layer  54  is laminated a magnetoresistive sensor having the structure shown in FIG. 1 or  3  and serving as a giant-magnetoresistive element. On the magnetoresistive sensor are further formed in turn an upper gap layer comprising alumina and an upper shielding layer. The upper shielding layer is also used as a lower core layer  55  of the inductive head h 2  provided on MR head h 1 . 
     The inductive head h 2  comprises the lower core layer  55 , a gap layer  64  formed on the lower core layer  55 , and a coil layer  66  formed on the gap layer  64 , patterned to a plane spiral form, and included in an insulating material layer  67 . The end  68   a  of an upper core layer  68  formed on the insulating material layer  67  is opposite to the lower core layer  55  with a small gap therebetween on the ABS surface  51   b , the base end  68   b  thereof being magnetically connected to the lower core layer  55 . On the upper core layer  68  is provided a protective layer  69  comprising alumina or the like. 
     In the inductive head h 2 , a recording current is given to the coil layer  66 , and given to the core layer from the coil layer  66 . A magnetic signal can thus be recorded on the recording magnetic medium such as a hard disk by the leakage magnetic field from the magnetic gap G between the ends of the lower core layer  55  and the upper core layer  68 . 
     In the MR head h 1 , since the resistance of the ferromagnetic layer  44  changes with the presence of the small leakage magnetic field from the recording magnetic medium such as the hard disk, recording contents of the recording medium can be read by reading the change in resistance. 
     Further, since the magnetic head HA constructed as described above comprises the magnetoresistive sensor having the above structure, it is possible to obtain a change in resistance with good linear response without generation of Barkhausen noise, and a higher MR ratio than a conventional magnetic head. The magnetic head HA thus has the property of excellent reading performance. 
     The magnetoresistive sensor having the structure shown in FIG. 1 can be formed by placing a substrate of Al 2 O 3 —TiC in a chamber of high frequency magnetron sputtering equipment or ion-beam sputtering equipment, and depositing required layers in turn in an inert gas atmosphere of Ar gas or the like in the chamber. The required targets for depositing the layers are an α-Al 2 O 3  target, a Ni—Fe alloy target, a Cu target, etc. 
     In manufacture of the magnetoresistive sensor of the present invention shown in FIG. 3, the coercive force increasing layer  41  comprising α-Al 2 O 3  is formed on the substrate by sputtering while applying a magnetic field in the Z direction shown in FIGS. 1 and 3 in an atmosphere under an Ar gas pressure of 3 mTorr or less, the two ferromagnetic layers  42  and  44  are formed on the coercive force increasing layer  41  to hold the non-magnetic layer  43  therebetween, and at the same time, portions of these layers other than a portion thereof corresponding to the track width are removed by a photolithography process and an ion milling method to form the laminate  45 . 
     The antiferromagnetic layers  46 , the amorphous ferromagnetic layers  47  and the electrically conductive layers  48  are then laminated on both ends of the laminate  45  by sputtering while applying a magnetic field at a right angle with the direction of previous application of the magnetic field. A magnetic field in the direction perpendicular to the drawing of FIG. 3 is then applied for permanent magnetization of the pinned ferromagnetic layer  42 . 
     The above-described treatment permits achievement of the magnetoresistive sensor having the structure shown in FIG. 3 in which the magnetization direction of the pinned ferromagnetic layer  42  is angled at 90° to the magnetization direction of the ferromagnetic layer  44 . 
     In manufacture of the magnetoresistive sensor having the structure shown in FIG. 1, the coercive force increasing layer  31 , the ferromagnetic layer  32 , the non-magnetic layer  33  and the ferromagnetic layer  34  are laminated, and then the antiferromagnetic layers and the electrically conductive layers are laminated. The central portions of the ferromagnetic layers and the electrically conductive layers are removed by the photolithographic process, and the upper protective layer  37  is formed thereon. In formation of each of these layers, the coercive force increasing layer  31  is deposited while applying a magnetic field in the direction corresponding to the Z direction shown in FIGS. 1 and 3, and the antiferromagnetic layers  35  are deposited while applying a magnetic field in the direction corresponding to the X direction shown in FIGS. 1 and 3. Finally, a magnetic field in the direction perpendicular to the drawing of FIG. 1 is applied for permanent magnetization of the pinned ferromagnetic layer  32 . 
     The above-described treatment permits achievement of the magnetoresistive sensor having the structure shown in FIG. 1 in which the magnetization direction of the pinned ferromagnetic layer  32  is angled at 90° to the magnetization direction of the ferromagnetic layer  34 . 
     EXAMPLES 
     On an Al 2 O 3 —TiC substrate coated with an Al 2 O 3  film was formed a laminate having the structure below by using high frequency magnetron sputtering equipment and a plurality of targets to manufacture a magnetoresistive sensor having the structure shown in FIG.  3 . 
     In this process, a coercive force increasing layer of α-Fe 2 O 3 , a ferromagnetic layer of an Ni 80 Fe 20  alloy, a non-magnetic layer of Cu, a ferromagnetic layer of an Ni 80 Fe 20  alloy and a protective layer of Ta had thicknesses of 500 Å, 30 Å, 20 Å, 75 Åand 30 Å, respectively. In order to provide the pinned ferromagnetic layer with anisotropy in the direction of the arrow b shown in FIG. 3, this layer was deposited while applying a magnetic field of 200 Oe in the direction of the arrow b. 
     Both end portions of the thus-obtained laminate were removed by the photolithography process and the ion milling method, leaving a portion having a track width (the width of the magnetic sensing portion) of 2 μm. On both sides of the left magnetic sensing portion were laminated, by sputtering, antiferromagnetic layers (Pt 50 Mn 50 ) having a thickness of 300 Å, amorphous layers (Co 88 Nb 8 Zr 4 ) having a thickness of 200 Å, and electrically conductive layers having a thickness of 700 Å. In this lamination, a magnetic field of 200 Oe was applied in the direction angled at 90° to with the direction of the previous applied magnetic field. 
     Finally, patterning is carried out so that a track width of 2 μm, and a height (the height in the direction perpendicular to the drawing of FIG. 3) of 1 μm were obtained, and a magnetic field of 2 kOe was applied in the height direction (the direction perpendicular to the drawing of FIG. 3) for permanent magnetization of the pinned ferromagnetic layer. 
     In some samples, annealing in a magnetic field was carried out at 250° C. for 5 hours while applying a magnetic field in the direction of the track width (the lateral direction of FIG. 3) before permanent magnetization in the height direction. 
     The magnetoresistance curve of the magnetoresistive sensor sample obtained by the above manufacturing method was measured in a low magnetic field. The results obtained are shown in Table 1 and FIG.  7 . In this measurement, the magnetic field was applied in the height direction. 
     
       
         
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 Magneto- 
                   
                   
                   
               
               
                   
                 resistance 
                   
                   
                   
               
               
                   
                 ratio 
                 Linearity 
                   
                 Barkhausen 
               
               
                 Ferromagnetic layer 
                 (±50 Oe) 
                 (±50 Oe) 
                 Hysteresis 
                 noise 
               
               
                   
               
             
             
               
                 Pt 50 Mn 50   
                 3.1% 
                 good 
                 no 
                 no 
               
               
                 Pd 50 Mn 50   
                 3.6% 
                 good 
                 no 
                 no 
               
               
                 Pd 30 Pt 20 Mn 50   
                 3.0% 
                 good 
                 no 
                 no 
               
               
                 Ni 50 Mn 50   
                 2.8% 
                 good 
                 no 
                 no 
               
               
                 Ru 50 Mn 50   
                 3.4% 
                 good 
                 no 
                 no 
               
               
                 Cr 52 Mn 48   
                 2.8% 
                 good 
                 no 
                 no 
               
               
                 Fe 51 Mn 49   
                 2.9% 
                 good 
                 no 
                 no 
               
               
                 Ir 15 Mn 85   
                 3.1% 
                 good 
                 no 
                 no 
               
               
                 Rh 20 Mn 80   
                 3.0% 
                 good 
                 no 
                 no 
               
               
                   
               
             
          
         
       
     
     FIG. 7 indirectly shows that the resistance value in zero magnetic field is at substantially the center between the maximum and minimum resistance values, and the magnetization directions cross at right angles. Since the resistance value in zero magnetic field is at substantially the center, it can be said that even if an external magnetic field changes within the range of about ±50 Oe, linearity is good, and the dynamic range is wide. It is also found that the sample exhibits neither hysteresis nor Barkhausen noise, and thus has preferable properties as a reading magnetic head. 
     The results indicate that the magnetoresistance ratio within a range of ±50 Oe is 3.1%, and the output is very high. Other samples were manufactured by the same method as described above except that the antiferromagnetic layers were deposited by respectively using PdMn, PdPtMn, NiMn, RuMn, CrMn, FeMn, IrMn, and RhMn in place of PtMn, and then measured by the same method. Table 1 indicates that the other samples also have excellent effects. 
     FIG. 8 shows the blocking temperature Tb of a magnetoresistive sensor sample comprising α-Fe 2 O 3  which was previously proposed by the inventors in Japanese Document No. A2 8-7235. For comparison, FIG. 8 also shows the temperature properties of a sample having the comparative structure (a laminate of NiFe/Cu/NiFe/FeMn (110 Å) and a laminate of NiFe/Cu/CoPt (80 Å)) disclosed in Japanese Document No. A2 8-7235, and a sample comprising NiO in place of FeMn. In FIG. 8, Hbp represents a bias magnetic field where the magnetization reversal of the NiFe film adjacent to the antiferromagnetic film was shifted, and Hcp represents the coercive force by this hysteresis. 
     The results shown in FIG. 8 indicate that the magnetoresistive sensor sample comprising α-Fe 2 O 3  also has excellent heat resistance. This is possibly due to the fact that the Neel temperature (677° C.) of α-Fe 2 O 3  is higher than those of FeMn and NiO. 
     Therefore, the magnetoresistive sensor sample comprising α-Fe 2 O 3  can provide a magnetoresistive sensor exhibiting less deterioration in properties due to a temperature change. 
     FIG. 9A shows the magnetizing curve of the pinned ferromagnetic layer adjacent to the coercive force increasing layer (α-Fe 2 O 3  or the like), and FIG. 9B shows the magnetoresistance curve of a spin-valve magnetoresistive sensor comprising the same pinned ferromagnetic layer. Each of FIGS. 9A and B shows the values of the coercive force (H c ) and the exchange bias magnetic field (H b ) which have the relation of H c &gt;H b . On the other hand, the ferromagnetic layers adjacent to the antiferromagnetic layers  46  have the reverse relation H c &lt;H b . In this case, unidirectional anisotropy is produced. In this specification, it is defined that unidirectional anisotropy occurs in the ferromagnetic layer having such a relation. 
     As described above, in the present invention, the ferromagnetic layers provided adjacent to the magnetoresistive element in the magnetic sensing region comprises an amorphous thin film. Since the amorphous ferromagnetic layer has a little MR effect, it is possible to produce a sensor having less side reading (reading a magnetic field of a recording magnetic medium in a region other than the track region) and less dispersion of unidirectional anisotropy. 
     The use of the antiferromagnetic layer for applying the longitudinal bias, which comprises X—Mn (wherein X indicates at least one of Pt, Pd, Ir, Ru and Rh) can provide a sensor having excellent corrosion resistance and less changes in the exchange anisotropic magnetic field with temperature changes. Within a composition range of X—Mn system alloys, a film of this alloy deposited by sputtering or the like can be used without any special heat treatment, and thus heat treatment conditions can be moderated, as compared with a conventional structure. 
     In use of the magnetoresistive sensor having the above structure as a magnetic head, the resistance changes in linear response to a small leakage magnetic field from a recording magnetic medium, and thus it is possible to provide a magnetic head capable of reading magnetic information with good sensitivity and no Barkhausen noise. 
     The unidirectional magnetic anisotropy induced in the ferromagnetic layer having free magnetization reversal, which is adjacent to the antiferromagnetic layer for applying the longitudinal bias, is produced by forming the ferromagnetic layer while applying a magnetic field thereto or performing heat treatment in a magnetic field after the formation of the ferromagnetic layer. In addition, the magnetization direction of the ferromagnetic layer having pinned magnetization reversal, which is adjacent to the coercive force increasing layer, is determined in the permanent magnetization process performed after the process for determining the magnetic anisotropy of the ferromagnetic layer having free magnetization reversal. It is thus possible to make the magnetization direction of the ferromagnetic layer having pinned magnetization reversal substantially perpendicular to the magnetization direction of the ferromagnetic layer having free magnetization reversal, and obtain a magnetoresistive sensor to which the longitudinal bias was applied. 
     Further, the unidirectional magnetic anisotropy induced in the ferromagnetic layer, which is adjacent to the antiferromagnetic layer to form a laminate, is produced by forming the ferromagnetic layer while applying a magnetic field thereto or performing heat treatment in a magnetic field after the formation of the ferromagnetic layer, and the magnetization direction of the ferromagnetic layer adjacent to the coercive force increasing layer and having pinned magnetization reversal is determined by the permanent magnetization process after the precess for determining the magnetic anisotropy of the ferromagnetic layer of the laminate. It is thus possible to make the magnetization direction of the ferromagnetic layer having pinned magnetization reversal substantially perpendicular to the magnetization direction of the ferromagnetic layer having free magnetization reversal, and obtain a magnetoresistive sensor to which the longitudinal bias was applied. 
     In the present invention, the antiferromagnetic layer comprising an antiferromagnetic material is provided for inducing the unidirectional magnetic anisotropy in the ferromagnetic layer having free magnetization reversal to stabilize the magnetic domain thereof. Therefore, it is possible to put the ferromagnetic layer into a single magnetic domain state. In addition, the magnetization direction of the ferromagnetic layer can be differentiated from the magnetization direction of the ferromagnetic layer having pinned magnetization reversal by an external magnetic field to produce a change in resistance. The external magnetic field can be detected by this change in resistance with good sensitivity, and the Barkhausen noise can be eliminated. Further, when the ferromagnetic layer is put into a single magnetic domain state, a magnetic field can be detected with excellent linear response. 
     Since the magnetization direction of the ferromagnetic layer having pinned magnetization reversal is at 90° with the magnetization direction of the ferromagnetic layer having free magnetization reversal, a high magnetoresistance ratio can be obtained efficiently. 
     When using an α-Fe 2 O 3  layer as the antiferromagnetic layer for pinning the magnetization direction, it is possible to provide a magnetoresistive sensor having high resistance to thermal changes and exhibiting no decrease in sensitivity by thermal changes because of the high Neel temperature of α-Fe 2 O 3 . 
     Further, the antiferromagnetic layers for applying the longitudinal bias are provided on both sides of the sensing region of the ferromagnetic layer having free magnetization reversal with a space therebetween which equals to the predetermined track width corresponding to the width of the sensing region so as to be adjacent to the ferromagnetic layer. Therefore, the longitudinal bias can be applied to both sides of the sensing region of the ferromagnetic layer due to the unidirectional magnetic anisotropy, and magnetization reversal of the magnetic sensing region of the ferromagnetic layer is facilitated. It is thus possible to obtain a change in resistance with good linear response and without Barkhausen noise when the longitudinal bias is applied. 
     Further, the ferromagnetic layer having free magnetization reversal is formed with the width of the magnetic sensing region corresponding to the track width, and a laminate of the antiferromagnetic layer comprising an antiferromagnetic material and another ferromagnetic layer is formed on either side of the ferromagnetic layer having free magnetization reversal. Thus, the longitudinal bias can be applied to the ferromagnetic layer due to the unidirectional magnetic anisotropy, and magnetization reversal of the ferromagnetic layer is facilitated. It is thus possible to obtain a change in resistance with good linear response and without Barkhausen noise when the longitudinal bias is applied.