Abstract:
A method is disclosed for fabricating a spin-valve magnetic head including a layered body of a first ferromagnetic layer having a first easy axis of magnetization extending in a first direction, a non-magnetic layer formed on the first ferromagnetic layer, a second ferromagnetic layer provided on the non-magnetic layer, and an anti-ferromagnetic layer provided on the second ferromagnetic layer in exchange coupling therewith. The method includes a first thermal annealing process with the steps of annealing the layered body in a first annealing state and applying a magnetic field to the layered body in a second direction different from the first direction, while maintaining the layered body in the first annealing state. The method further includes a second thermal annealing process with the steps of annealing the layered body, after the first thermal annealing process, in a second annealing state and applying a magnetic field in a third direction different from the second direction while maintaining the layered body in the second annealing state.

Description:
This is a divisional of application Ser. No. 09/024,074, filed Feb. 17, 1998, now U.S. Pat. No. 6,034,845. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to magnetic heads and more particularly to an improvement of a GMR (giant magneto-resistance) head having a so-called spin-valve structure. 
     A GMR head is a high-sensitivity magnetic head that detects a change of resistance of a magnetic layer that in turn occurs in response to a change of direction of a very weak external magnetic field. Because of the high magnetic sensitivity, a GMR head is expected to play a major role in a high-density magnetic recording apparatus as a high-resolution and high-sensitivity magnetic head. 
     FIG. 1 shows the overall construction of a magnetic head  10  having a typical conventional spin-valve structure, while FIG. 2 shows the construction of a spin-valve head  14  used in the magnetic head of FIG.  1 . 
     Referring to FIG. 1, the magnetic head  10  includes a lower magnetic shield layer  12  of a magnetic material such as FeNi, CoFe or FeN provided on a substrate  11  of Al 2 TiC. On the foregoing lower magnetic shield layer  12 , there is provided a spacer layer  13  of a non-magnetic material such as Al 2 O 3 , and a magnetic sensor  14  having a spin-valve structure is formed on the spacer layer  13 . 
     The magnetic sensor  14  is covered by another spacer layer  15  also of a non-magnetic material similar to the spacer layer  13 , and an upper magnetic shield layer  16  of a soft magnetic material such as FeNi or CoFe is provided on the spacer layer  15 . Thereby, the spacer layer  13 , the magnetic sensor  14  and the spacer layer  15  form together a minute  1  magnetic read gap between the upper and lower magnetic shield layers  12  and  16  with a size of about 200 nm. 
     On the upper magnetic shield layer  16 , there is provided another spacer layer  17  of a non-magnetic material with a thickness of about 350 nm, and a coil pattern  19  is provided on the spacer layer  17  with an intervening insulation layer  18 , wherein the insulation layer  18  continuously has a reducing thickness toward a front end  10 A of the magnetic head  10 . The coil pattern  19  is covered by another insulation layer  20 , and a magnetic pole  21  of a magnetic material such as FeNi or CoFe is provided on the foregoing another insulation layer  20  such that the thickness of the insulation layer  20  decreases continuously toward the foregoing front end  10 A of the magnetic head  10 . As a result of the decreasing thickness of the insulation layers  18  and  20  at the front end  10 A of the magnetic head  10 , the magnetic pole  21  makes direct contact with the spacer layer  17  at the front end  10 A. There a minute magnetic write gap is formed between the upper magnetic shield  16  and the magnetic pole  21 . It should be noted that the upper magnetic shield  16  extends to the magnetic pole  21  at a part not illustrated in FIG. 1, and a magnetic circuit is formed. 
     The magnetic head  10  scans the surface of a magnetic recording medium such as a magnetic disk at the foregoing front edge surface  10 A, and the magnetic sensor  14  detects the magnetization recorded on the surface of the magnetic recording medium at the foregoing magnetic read gap. Further, a recording of information is made on the magnetic recording medium at the foregoing write gap by energizing the coil  19  by an information signal. 
     FIG. 2 shows the construction of the magnetic sensor  14  in detail, wherein those parts explained already with reference to FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. 
     Referring to FIG. 2, the magnetic sensor  14  includes a magnetic detection layer or so-called “free layer”  14 A of a soft magnetic material such as CoFe or NiFe formed on the spacer layer  14 , wherein the free layer changes the direction of magnetization freely in response to the magnetization of the magnetic recording medium. 
     On the free layer  14 A, there is provided an intermediate layer  14 B of a non-magnetic material such as Cu, and a fixed magnetization layer or so-called “pinned layer”  14 C is provided on the intermediate layer  14 B with a predetermined fixed magnetization, wherein the pinned layer  14 C is formed of a soft magnetic material such as CoFe or NiFe similarly to the free layer  14 B. It should be noted that the magnetization of the pinned layer  14 C is fixed in the direction of magnetization of a magnetization-fixing layer or so-called “pinning layer”  14 D, wherein the pinning layer  14 D is formed of an anti-ferromagnetic material such as FeMn or PdPtMn and provided on the pinned layer  14 C. It should be noted that the pinning layer  14 D fixes the magnetization of the pinned layer  14 C by spin-exchange interaction. Thereby, the magnetization of the magnetic recording medium is detected by detecting a change of electric resistance that occurs in response to the change of direction of magnetization in the free layer  14 A with respect to the direction of magnetization in the pinned layer  14   c.  In FIGS. 1 and 2, it should be noted that the electrodes for detecting the foregoing resistance change is omitted from illustration. Further, it should be noted that the pinning layer  14 D, lacking a spontaneous magnetization, is relatively immune to the external magnetic field. 
     In the magnetic sensor  14  having such a construction, in which the direction of magnetization of the free layer  14 A changes in response to the direction of magnetization of the magnetic recording medium, it should be noted that the resistance of the magnetic sensor  14  becomes minimum when the direction of magnetization of the layer  14 A is parallel to the direction of the magnetization of the pinned layer  14 C. When the direction of magnetization of the layer  14 A is in an anti-parallel relationship with the direction of magnetization of the pinned layer  14 C, on the other hand, the resistance of the magnetic sensor  14  becomes maximum. 
     In the case of using the magnetic sensor  14  for the magnetic head  10 , it is advantageous to set the direction of magnetization of the pinned layer  14 C perpendicular to the direction of magnetization of the free layer  14 A in a free state in which there is no external magnetic field applied to the magnetic sensor  14 . See FIG.  3 A. By doing so, the resistance of the magnetic sensor  14  is increased or decreased generally symmetrically depending on whether the magnetization of the magnetic recording medium is parallel or anti-parallel to the magnetization of the pinned layer  14 C, as indicated in FIG.  3 B. Such a generally symmetric increase and decrease of the resistance facilitates the signal processing in the magnetic recording and reproducing apparatus. 
     It should be noted that the control of magnetization of a magnetic body is conducted in a heat treatment process. 
     FIG. 4 shows a heat treatment process conducted conventionally in the process of forming the spin-valve structure of FIG.  2 . 
     Referring to FIG. 4, the spin valve structure of FIG. 2 is formed in a step  1  of FIG. 4 by depositing the layers  14 A- 14 D under the existence of an initial magnetic field with a predetermined initial direction designated as a 0° direction. The free layer  14 A thus formed has an easy axis of magnetization in the foregoing 0° direction. 
     Next, in the step  2  of FIG. 4, the spin-valve structure of FIG. 2 is subjected to a thermal annealing process to a temperature close to a blocking temperature of the pinning layer  14 D, and a magnetic field is applied in the foregoing 0° direction as indicated by blank arrows. As a result, the direction of magnetization of the pinned layer  14 C is aligned in the 0° direction. 
     FIGS. 5A and 5B explain the blocking temperature. 
     In a magnetic system in which an anti-ferromagnetic layer and a soft magnetic layer form an exchange coupling as in the case of the spin-valve structure of FIG. 2, it should be noted that the hysteresis curve of the magnetic system is displaced along the horizontal axis representing the magnetic field H by an amount Hua as indicated in FIG. 5A as a result of the pinning of magnetization caused in the soft magnetic layer such as the pinned layer  14 C by the anti-ferromagnetic pinning layer  14 D. This phenomenon means that it is insufficient in a magnetic system that includes such an anti-ferromagnetic layer, to apply a magnetic field just enough to cause an inversion of magnetization in an ordinary magnetic system not including an anti-ferromagnetic layer, for causing an inversion of magnetization. In order to achieve this, it is necessary to increase the magnetization by an amount Hua, This is the pinning of magnetization. 
     FIG. 5B shows the temperature dependence of the quantity Hua. 
     Referring to FIG. 5B, it should be noted that the quantity Hua decreases with increasing temperature and reaches zero at a blocking temperature T B . In other words, the magnetization of the spin valve structure of FIG. 2 can be controlled as desired by an external magnetic field when the system is heated to a temperature close to or higher than the blocking temperature T B . The pinning of magnetization in such a magnetic system is eliminated when the system is heated to the blocking temperature T B  or higher. 
     Referring back to FIG. 4, the pinned layer  14 C is magnetized in the foregoing 0° direction as a result of the thermal annealing process conducted at the temperature close to the blocking temperature T B , and the anti-ferromagnetic pinning layer  14 D forms an exchange coupling with the pinned layer  14 C. By cooling the structure thus formed to room temperature environment in the step  3  of FIG. 4, a structure in which the pinned layer  14 C is magnetized in the 0° direction is obtained. In the structure of step  3  of FIG. 4, the magnetization of the pinned layer  14 C is pinned by the pinning layer  14 D. As a result of the thermal annealing process in the step  2  of FIG. 4, the magnetic shield layers  12  and  16  and the magnetic pole  21  forming the magnetic head  10  of FIG. 1 are all magnetized in the foregoing 0° direction. 
     Next, in the step  4  of FIG. 4, the structure of step  3  of FIG. 4 is heated to a temperature close to the blocking temperature T B  again, and an external magnetic field is applied to the spin valve structure in a direction perpendicular to the foregoing 0° direction. As a result, the magnetization of the pinned layer  14 C is rotated by 90°, and a structure shown in step  5  of FIG. 4 is obtained, in which it should be noted that the direction of magnetization of the pinned layer  14 C is perpendicular to the direction of easy axis of magnetization of the free layer  14 A. 
     In the process of FIG. 4, however, there arises a problem, associated with the fact that the entire magnetic head  10  including the spin-valve magnetic sensor  14  is heated to the temperature close to the blocking temperature T B , in that the direction of magnetization of the magnetic shields  12  and  16  or the direction of magnetization of the magnetic pole  21 , which has been initialized in the step  2 , may be changed unwontedly. Further, such thermal annealing and magnetization processes conducted at the temperature close to the blocking temperature may cause a 90° rotation in the easy axis of magnetization from the desired 0° direction as indicated by a broken arrow in step  5  of FIG.  4 . When this occurs, the detection characteristic of the magnetic sensor  14  is modified from the characteristic of FIG.  3 B and the magnetic sensor  14  would produce an asymmetric output in response to the magnetization of the magnetic recording medium. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a general object of the present invention to provide a novel and useful magnetic head, a fabrication process thereof, and a magnetization control method of a magnetic film, wherein the foregoing problems are eliminated. 
     Another and more specific object of the present invention is to provide a magnetic head using a spin-valve magnetic sensor wherein the direction of easy axis of magnetization of a free layer is set perpendicular to the direction of magnetization of a pinned layer. 
     Another object of the present invention is to provide a spin-valve magnetic head, comprising: 
     a first ferromagnetic layer having a first easy axis of magnetization extending in a first direction; 
     a second ferromagnetic layer provided on said first ferromagnetic layer with a separation therefrom, said second ferromagnetic layer having a magnetization in a direction substantially perpendicular to said first easy axis of magnetization; and 
     an anti-ferromagnetic layer provided on said second ferromagnetic layer in exchange coupling therewith; 
     said second ferromagnetic layer having a second easy axis of magnetization extending in a direction intersecting said second direction. 
     Another object of the present invention is to provide a method of fabricating a spin-valve magnetic head including a layered body of a first ferromagnetic layer having a first easy axis of magnetization extending in a first direction, a non-magnetic layer formed on said first ferromagnetic layer, a second ferromagnetic layer provided on said non-magnetic layer, and an anti-ferromagnetic layer provided on said second ferromagnetic layer in exchange coupling therewith, said method comprising: 
     a first thermal annealing process including the steps of: annealing said layered body in a first annealing state; and applying a magnetic field to said layered body in a second direction different from said first direction while maintaining said layered body in said first annealing state; and 
     a second thermal annealing process including the steps of: annealing said layered body, after said first thermal annealing process, in a second annealing state; and applying a magnetic field in a third direction different from said second direction while maintaining said layered body in said second annealing state. 
     Another object of the present invention is to provide a method of fabricating a spin-valve magnetic head including a layered body of a first ferromagnetic layer having a first easy axis of magnetization extending in a first direction, a non-magnetic layer formed on said first ferromagnetic layer, a second ferromagnetic layer provided on said non-magnetic layer, and an anti-ferromagnetic layer provided on said second ferromagnetic layer in exchange coupling therewith, said method comprising the steps of: 
     annealing said layered body; and 
     applying a magnetic field to said layered body in a second direction different from said first direction while annealing said layered body; 
     wherein said second direction intersects said first direction with an angle exceeding 90°. 
     Another object of the present invention is to provide a method of magnetizing a magnetic system including a ferromagnetic layer magnetized in a first direction and an anti-ferromagnetic layer provided on said ferromagnetic layer in exchange coupling therewith, said method comprising: 
     a first thermal annealing process including the steps of: annealing said magnetic system in a first annealing state; and applying a magnetic field to said magnetic system in a second direction different from said first direction while maintaining said magnetic system in said first annealing state; and 
     a second thermal annealing process including the steps of: annealing said magnetic system, after said first thermal annealing process, to a second annealing state; and applying a magnetic field in a third direction different from said second direction while maintaining said magnetic system in said second annealing state. 
     Another object of the present invention is to provide a method of magnetizing a magnetic system including a ferromagnetic layer magnetized in a first direction and an anti-ferromagnetic layer provided on said ferromagnetic layer in exchange coupling therewith, said method comprising: 
     annealing said magnetic system; and 
     applying a magnetic field to said magnetic system in a second direction different from said first direction while annealing said magnetic system, to cause a rotation of magnetization in said ferromagnetic layer to a desired angle; 
     wherein said second direction intersects said first direction with an angle exceeding said desired angle. 
     According to the present invention, the annealing process for rotating the magnetization of the second ferromagnetic layer is conducted at a low temperature set such that no substantial rotation occurs in the easy axis of magnetization of the first as well as second ferromagnetic layers. As the temperature used for the annealing process is set low as such, the process of rotating the magnetization may be conducted in plural times by rotating the direction of the external magnetic field stepwise each time. In this case, it is particularly advantageous to set the direction of the external magnetic field to a direction exactly opposing the first direction in the final annealing process. Thereby, the easy axis of magnetization of the first ferromagnetic layer is aligned exactly to the first direction even when the direction of the easy axis of magnetization is offset slightly as a result of the annealing processes. When the rotation of magnetization of the second ferromagnetic layer is to be conducted in a single step, on the other hand, the direction of the external magnetic field is set with an excessive, offset angle with respect to the desired direction of magnetization. 
     As a result of the low temperature heat treatment processes, other magnetic members or parts of the magnetic head are not affected or deteriorated even when the annealing is applied repeatedly for causing the desired rotation of the magnetization, and the magnetic head shows a near-ideal resistance change as indicated in FIG.  3 B. In the magnetic head of the present invention, the direction of magnetization of the second ferromagnetic layer does not coincide with the direction of the easy axis of magnetization thereof. 
    
    
     Other objects and further features of the present invention will become apparent from the following detailed description when read in conjunction with the attached drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram showing the construction of a conventional magnetic head that uses a conventional spin-valve magnetic sensor; 
     FIG. 2 is a diagram showing the construction of a conventional spin-valve magnetic sensor; 
     FIGS. 3A and 3B are diagrams showing the principle of an ideal spin-valve magnetic sensor that changes a resistance value thereof symmetrically with the direction of magnetization of a recording medium; 
     FIG. 4 is a diagram showing a conventional process of forming the spin-valve magnetic sensor of FIG. 2; 
     FIGS. 5A and 5B are diagrams explaining the blocking temperature; 
     FIG. 6 is a diagram showing the fundamental construction of the spin-valve magnetic sensor according to the present invention; 
     FIG. 7 is a diagram showing the fabrication process of a magnetic head according to a first embodiment of the present invention; 
     FIGS. 8A-8C are diagrams showing a rotation of magnetization or easy axis of magnetization that occurs in a magnetic layer in the thermal annealing processes of FIG. 7; 
     FIG. 9 is a diagram showing the fabrication process of a magnetic head according to a second embodiment of the present invention; and 
     FIGS. 10A and 10B are diagrams showing a rotation of magnetization occurring in a magnetic layer in the thermal annealing processes of FIG.  9 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     [First Embodiment] 
     FIG. 6 shows the construction of a spin-valve magnetic sensor  30  according to a first embodiment of the present invention wherein the spin-valve magnetic sensor  30  is used in the magnetic head  10  of FIG. 1 in place of the spin-valve magnetic sensor  14 . 
     Referring to FIG. 6, the spin-valve magnetic sensor  30  includes a Ta film  31  formed on the spacer layer  13  with a thickness of about 10 nm, and a NiFe film  32   a  is formed on the Ta film  31  with a thickness of about 2 nm. On the NiFe film  32   a,  there is provided a CoFe film  32   b  with a thickness of about 5.5 nm, wherein the films  32   a  and  32   b  form a ferromagnetic free layer  32  corresponding to the free layer  14 A of FIG.  2 . 
     In the structure of FIG. 6, a non-magnetic layer  33  of Cu is formed in correspondence to the non-magnetic layer  14 B of FIG. 2 with a thickness about 3.5 nm, and a pinned layer  34  of CoFe is formed on the non-magnetic layer  33  in correspondence to the ferromagnetic pinned layer  14   c  of FIG. 2, with a thickness of about 3.5 nm. On the pinned layer  34 , there is formed a pinning layer  35  of PdPtMn in correspondence to the pinning layer  14 D with a thickness of about 25 nm. The pinning layer  35  is formed directly on the pinned layer  34  and establishes an exchange coupling with the layer  35 . It should be noted that the pinning layer  35  has a blocking temperature of about 300° C. 
     FIG. 7 shows the thermal annealing process conducted on the structure of FIG. 6 according to a first embodiment of the present invention, wherein it should be noted that the thermal annealing process of FIG. 7 is conducted in a state that the spin-valve magnetic sensor  30  is attached integrally to the magnetic head  10 . 
     Referring to FIG. 7, the structure of FIG. 2 is formed in the step  1  while applying a predetermined magnetic field in a predetermined direction, and the free layer  32  thus formed has the magnetization as well as the easy axis of magnetization in the direction shown in the step  1  with a solid arrow. This direction is defined as a “0° direction.” 
     Next, in the step  2 , the spin-valve sensor  30  is held in a d.c. magnetic field of 2.5 kOe and annealed at a temperature of about 25° C. for about 3 hours. As a result of the thermal annealing process of the step  2 , the direction of magnetization and the direction of easy axis of magnetization are aligned in the 0° direction as indicated by a solid arrow in the step  3  of FIG.  7 . The thermal annealing process of the step  2  of FIG. 7 is conducted in a high vacuum environment in which the pressure is set to 1.5×10 −5  Pa or lower. The state of the step  3  is designated as initial state. As a result of the thermal annealing process in the step  2 , the magnetic shield layers  12  and  16  and further the magnetic pole  21  are magnetized in the initial step  3  of FIG. 7 in the foregoing 0° direction. 
     Next, in the step  4  of FIG. 7, the spin-valve magnetic sensor  30  is applied with an external magnetic field acting perpendicularly to the foregoing 0° direction and a thermal annealing process is applied at a temperature of about 210° C. for about 2 hours. It should be noted that the temperature of 210° C. is substantially lower than the temperature of 250° C. used in the thermal annealing process in the step  2  of FIG.  7 . In the thermal annealing process of the step  4 , the magnitude of the external magnetic field is set identical to the case of the step  2 , and the thermal annealing process is conducted under the high vacuum environment of 1.5×10 −5  Pa or lower in pressure. 
     FIG. 8A shows the change of direction of the magnetization in the pinned layer  34  for the case in which the temperature of the thermal annealing process is changed from 210° C. to 250° C. As already noted, the external magnetic field is applied in the direction substantially perpendicular to the initial magnetization direction similarly to the step  4  of FIG.  7 . In FIG. 8A, the duration of the thermal annealing process is set to 3 hours, which is slightly longer than the duration used in the step  4  of FIG.  7 . 
     Referring to FIG. 8A, it can be seen that the magnetization of the pinned layer  34  causes a rotation of about 84° when the temperature of the thermal annealing process is set to 250° C. in the step  4  similarly to the case of the step  2  of FIG.  7 . However, the amount of rotation is decreased to about 77° when the temperature of the thermal annealing process is reduced to about 230° C. Further, the amount of rotation is reduced to about 67° when the temperature of the thermal annealing process is reduced to about 210°, which is the temperature used in the step  4  of FIG.  7 . 
     This means that the full 90° rotation of the magnetization is not possible in the low temperature thermal annealing process used in the step  4  of FIG. 7, even when the duration of the thermal annealing process is continued for 3 hours or more, and the direction of magnetization of the pinned layer  34  obtained in the thermal annealing process of the step  4  forms an intermediate angle between the 0° direction and the 90° direction. Further, the free layer  32  may also cause some rotation of magnetization as a result of the thermal annealing process in the step  4  of FIG.  7 . 
     Thus, in the present invention, a step  6  shown in FIG. 7 is conducted after the step  5 , in which an external magnetic field acting in the substantially opposing direction (180°) to the foregoing 0° direction is applied to the spin-valve magnetic sensor  30 , and a thermal annealing process is conducted at a temperature of about 210° C. for 2 hours in this state similarly to the thermal annealing process in the step  4  of FIG.  7 . As a result of the thermal annealing process of the step  6 , the magnetization of the pinned layer  34  now extends in the direction perpendicular to the initial 0° direction as indicated in the step  7  of FIG.  7 . In the step  7 , it should further be noted that, as a result of the thermal annealing process conducted under the existence of the external magnetic field acting in the 180° direction, the magnetization of the free layer  32 , which has been slightly offset from the 0° direction in the step  5 , is once again aligned to the initial 0° direction. 
     FIG. 8B shows the rotation of the magnetization of the pinned layer  34  occurring in each of the thermal annealing steps  2 ,  4  and  6  represented respectively as A, B and C. As can be seen in FIG. 8B, the 90° rotation of the magnetization is successfully achieved by repeating the thermal annealing steps. In the point B corresponding to the step  4 , it should be noted that the amount of rotation is about 45°, which is smaller than the rotation angle of about 67° shown in FIG. 8A for the same temperature. This discrepancy between these different rotational angles is caused merely as a result of the difference in the duration of the thermal annealing process in the experiment of FIG.  8 A and in the experiment for FIG.  8 B. 
     As already explained with reference to FIGS. 3A and 3B, the spin-valve magnetic sensor  30  of the present embodiment increases or decreases the resistance depending on the direction of magnetization on a recording medium symmetrically. 
     FIG. 8C shows the rotation of the easy axis of magnetization of the free layer  32  for the case in which the temperature of the thermal annealing process is changed in the step  4  of FIG.  7 . 
     Referring to FIG. 8C, the easy axis of magnetization rotates significantly when the thermal annealing process of the step  4  is conducted at the conventional temperature of about 250° C. On the other hand, the easy axis of magnetization rotates little when the thermal annealing process is conducted at the temperature of about 210° C. as in the case of the present invention. Even if such a rotation occurred, the magnitude of the rotational angle is limited without 10°. The same applies also to the thermal annealing process conducted at 230° C. 
     In relation to the finding of FIG. 8C, it should be noted that the thermal annealing process at 210° C. does not cause a rotation of easy axis of magnetization in the pinned layer  34  that has a composition substantially identical to the composition of the free layer  32 , as indicated by a broken line in the step  7  of FIG.  7 . In other words, the spin valve magnetic  30  that has been applied with a low temperature thermal annealing process for causing the rotation of magnetization of the pinned layer characteristically shows a feature that the direction of magnetization and the direction of easy axis of magnetization are different in the pinned layer  34 . 
     In the present embodiment, it is also possible to conduct the process of the step  4  of FIG. 7 in plural times each with a reduced duration for the thermal annealing process. 
     [Second Embodiment] 
     FIG. 9 shows a fabrication process of the spin valve magnetic sensor  30  according to a second embodiment of the present invention, wherein those parts corresponding to the parts described previously are designated by the same reference numerals and the description thereof will be omitted. It should be noted that the magnetic sensor  30  itself has a construction described already with reference to FIG.  6 . 
     Referring to FIG. 9, the spin valve magnetic sensor  30  is subjected, after the process of the steps  1 - 3  corresponding to the steps  1 - 3  of FIG. 7, a thermal annealing process which is conducted in a high vacuum environment at 210° C. under the existence of an external magnetic field, wherein the direction of the external magnetic field is set such that the magnetization of the pinned layer  34  intersects perpendicularly, after the step  4  of FIG. 9, to the initial 0° direction of magnetization in the step  3 . 
     As explained already, the angle that the magnetization of the pinned layer  34  forms with the initial 0° direction of magnetization becomes smaller than 90° when the direction of the external magnetic field is set perpendicularly to the foregoing initial direction of magnetization. Thus, in order to achieve the foregoing 90° angle for the magnetization of the pinned layer  34  from the 0° direction, the present embodiment sets an offset angle in the direction of the external magnetic field such that the external magnetic field forms an angle larger than 90° with respect to the initial direction of magnetization. 
     FIG. 10A shows the relationship between the direction of the external magnetic field in the step  4  of FIG.  9  and the actual direction of magnetization of the pinned layer  34 , wherein FIG. 10A shows the result for the case in which the external magnetic field has an intensity of 1.5 kOe and the thermal annealing process is continued for 3 hours. 
     Referring to FIG. 10A, the desired perpendicular intersection of the magnetization of the pinned layer  34  with respect to the initial direction of magnetization is achieved successfully, when the thermal annealing process is conducted at 210° C., by setting the angle of the external magnetic field to about 115°, which is about 25° larger than the nominal 90° angle. When the thermal annealing process is conducted at 230° C., this offset angle is reduced to about 10°. 
     Thus, it is possible to reduce the offset angle of the external magnetic field by increasing the temperature of the thermal annealing process. However, such an increase of the thermal annealing process applied to the magnetic head  10 , in which the magnetic sensor  30  is included, tends to induce a deterioration in the magnetization of the magnetic shield layers  12  and  16  or in the magnetization of the magnetic pole  21 , as explained already. Thus, in order to avoid such adversary problems, it is preferable to conduct the thermal annealing process at the temperature lower than about 210° C. in which no substantial rotation occurs in the easy axis of magnetization of the free layer  32 . 
     FIG. 10B shows the rotation of magnetization of the pinned layer  34  in the step  4  of FIG. 9 for the case in which the duration of the thermal annealing process is changed. 
     Referring to FIG. 9B, it can be seen that the rotational angle increases generally with the duration of thermal annealing process up to about 3 hours. This in turn means that the duration of the thermal annealing process may be reduced by setting the offset angle of the external magnetic field somewhat larger in the step  4  of FIG.  5 . 
     In the present embodiment, as well as in the previous embodiment, the thicknesses and compositions of the free layers  32   a  and  32   b,  non-magnetic layer  33 , pinned layer  34  and the pinning layer  35  are not limited to those described previously but other thicknesses and other compositions may also be used. Particularly, the pinning layer  35  may be formed of a material other than PdPtMn such as NiMn, PtMn, PdMn, IrMn, RhMn and an alloy thereof. 
     Further, the present invention is by no means limited to those embodiments described heretofore, but various variations and modifications may be made without departing from the scope of the invention.