Patent Publication Number: US-2006002031-A1

Title: Magnetic sensing device and method of forming the same

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a magnetic sensing device capable of sensing a change in a signal magnetic field at high sensitivity and a method of forming the same.  
      2. Description of the Related Art  
      Generally, a magnetic recording/reproducing apparatus for writing/reading magnetic information to/from a recording medium such as a hard disk has a thin film magnetic head including a magnetic recording head and a magnetic reproducing head. The reproducing head has a giant magnet-resistive effect element (hereinbelow, GMR element) executing reproduction of a digital signal as magnetic information by using so-called giant magnet-resistive effect.  
      The GMR element used for a thin film magnetic head generally has a spin valve structure as shown in  FIG. 17 . Concretely, the GMR element is a stacked body  120  including a pinned layer  121  whose magnetization direction is pinned in a predetermined direction, a free layer  123  whose magnetization direction changes according to an external magnetic field, and an intermediate layer  122  sandwiched between the pinned layer  121  and the free layer  123  (refer to, for example, U.S. Pat. Nos. 5,159,513 and 5,206,590). Each of the top face (the face on the side opposite to the intermediate layer  122 ) of the pinned layer  121  and the under face (the face on the side opposite to the intermediate layer  122 ) of the free layer  123  is protected with a not-shown protection layer. In the pinned layer  121 , specifically, as shown in  FIG. 18  for example, a magnetization pinned film  124  and an antiferromagnetic film  125  are stacked in order from the side of the intermediate layer  122 . The magnetization pinned film  124  may be a single layer or a synthetic layer in which a ferromagnetic layer  141 , an exchange coupling film  142 , and a ferromagnetic layer  143  are formed in order from the side of the intermediate layer  122  as shown in  FIG. 19 . The free layer  123  may be a single layer or may have a configuration that, for example as shown in  FIG. 20 , a ferromagnetic film  131 , an intermediate film  132 , and a ferromagnetic film  133  are formed in order from the side of the intermediate layer  122  and the ferromagnetic films  131  and  133  are exchange-coupled. Such a spin valve structure is formed by a method of sputtering, vacuum deposition, or the like.  
      The materials and the like of the pinned layer and the free layer in the GMR element used for a thin film magnetic head are disclosed in, for example, U.S. Pat. No. 5,549,978. The material of the intermediate layer sandwiched by the pinned layer and the free layer is generally, for example, copper (Cu). A GMR element capable of using so-called tunnel effect obtained by making a very thin intermediate layer (tunnel barrier layer) of an insulating material such as aluminum oxide (Al 2 O 3 ) in place of copper was also developed.  
      In the GMR element used for a thin film magnetic head, the magnetization direction of the free layer freely changes according to a signal magnetic field generated from a magnetic recording medium. At the time of reading magnetic information recorded on a magnetic recording medium, for example, read current is passed along a stacked-body in-plane direction to the GMR element. At this time, the read current displays an electric resistance value which varies according to the state of the magnetization direction of the free layer. Consequently, a change in the signal magnetic field generated from the recording medium is detected as a change in electric resistance.  
      This phenomenon will be described in more detail by referring to  FIGS. 21A and 21B .  FIGS. 21A and 21B  show the relation between the magnetization directions of the pinned layer  121  and free layer  123  and the electric resistance of the read current in the spin valve structure. The magnetization direction of the pinned layer  121  is indicated by reference numeral J 121  and that of the free layer  123  is indicated by reference numeral J 123 .  FIG. 21A  shows a state where the magnetization directions of the pinned layer  121  and the free layer  123  are parallel to each other, and  FIG. 21B  shows a state where the magnetization directions of the pinned layer  121  and the free layer  123  are anti-parallel to each other. In  FIGS. 21A and 21B , in the case of passing read current in the stacked-body in-plane direction, it is estimated that the read current flows mainly in the intermediate layer  122  having high electric conductivity. Electrons “e” flowing in the intermediate layer  122  are subjected to either scattering (which contributes to increase in electric resistance) or mirror-reflection (which does not contribute to increase in electric resistance) in an interface K 123  with the free layer  123  and an interface K 121  with the pinned layer  121 . In the case where the magnetization directions J 121  and J 123  are parallel to each other as shown in  FIG. 21A , the electrons “e” having spins Se parallel to the directions are not so scattered by the interfaces K 121  and K 123  and display relatively low electric resistance. However, in the case where the magnetization directions J 121  and J 123  are anti-parallel to each other as shown in  FIG. 21B , the electrons “e” are easily scattered by the interface K 121  or K 123  and relatively high electric resistance is displayed.  FIG. 21B  shows a state where the electron “e” having the spin Se to the right side of the drawing sheet is scattered by the interface K 123  with the free layer  123 . As described above, in the GMR element having the spin valve structure, electric resistance of the read current changes according to the angle of the magnetization direction J 123  with respect to the magnetization direction J 121 . Since the magnetization direction J 123  is determined by the external magnetic field, as a result, a change in the signal magnetic field from a recording medium can be detected as a resistance change in the read current.  
      Usually, a GMR element having the spin valve structure is constructed so that the magnetization direction of the free film (free layer) and that of the magnetization pinned film (pinned layer) are orthogonal to each other when an external magnetic field is not applied (H=0). The direction of the easy axis of magnetization of the free layer is set to be the same as the magnetization direction of the pinned layer. The GMR element with such a configuration is disposed so that the magnetization direction of the pinned layer is parallel to the direction of application of the external magnetic field. In such a manner, the center point of an operation range of the magnetization direction in the free layer can be set to the state where no external magnetic field is applied (H=0). That is, the state where the external magnetic field is zero can be set to the center of an amplitude of electric resistance which can be changed by a change in the external magnetic field. Consequently, it is unnecessary to apply a bias magnetic field to the GMR element.  
      The above will be concretely described with reference to  FIGS. 22A  to  22 C and  FIG. 23 .  FIGS. 22A  to  22 C show a state where magnetic information on a recording medium is read by a thin film magnetic head on which the GMR element is mounted in a general hard disk drive. As shown in  FIG. 22A , the GMR element  120  is disposed close to the recording face  110  of a recording medium so that the magnetization direction J 121  of the pinned layer  121  is the +Y direction which is the direction (Y axis direction) orthogonal to the recording face  110  of the recording medium and the magnetization direction J 123  of the free layer  123  is the +X direction which is the direction (X axis direction) of the track width of the recording medium. It is assumed that there is no influence of the signal magnetic field from the recording medium at this point. When the hard disk drive is driven and, for example as shown in  FIG. 22B , a magnetic field in a signal magnetic filed direction J 110  in the −Y direction is generated from a recording medium, the magnetization direction J 123  becomes the −Y direction which is the opposite to the magnetization direction J 121 . Therefore, the resistance value of the read current increases as described with reference to  FIG. 23 . On the other hand, for example, in the case where a signal magnetic field in the signal magnetic field direction J 110  from the recording medium is in the +Y direction as shown in  FIG. 22C , the magnetization direction J 123  becomes the +Y direction which is the same as the magnetization direction J 121 . Therefore, the resistance value of the read current decreases. By making, for example, the state of  FIG. 22B  associated with “0” and making the state of  FIG. 22C  associated with “1” by using the resistance change, the signal magnetic field can be detected as binary information. As obvious from  FIGS. 22A  to  22 C, the center of the amplitude of the magnetization direction J 123  corresponds to the state of  FIG. 22A  (H=0).  FIG. 23  shows the relation between the external magnetic field (signal magnetic field) H and electric resistance R in the GMR element  120 . In  FIG. 23 , the external magnetic field in the −Y direction in  FIGS. 22A  to  22 C is set as H&gt;0 and that in the +Y direction is set as H&lt;0. As shown in  FIG. 23 , as the intensity of the signal magnetic field in the −Y direction increases, the electric resistance R increases and is saturated in the end. As the intensity of the signal magnetic field in the +Y direction increases, the electric resistance R decreases and is saturated in the end. In such a manner, the electric resistance R changes around the state where the external magnetic field H is zero as a center. Therefore, the GMR element having the spin-valve structure in which the magnetization direction of the free layer and that of the pinned layer are orthogonal to each other at the zero magnetic field does not have to have bias applying means, so that it is generally applied to read magnetic information recorded on a hard disk, a flexible disk, a magnetic tape, or the like. Orthogonalization of the magnetization directions is realized by performing, mainly, a regularization heat treatment process which determines the magnetization direction of the pinned layer and an orthogonalization heat treatment process which follows the regularization heat treatment process and determines the magnetization direction of the free layer.  
       FIGS. 24A  to  24 C show the outline of a process of forming the stacked body  120  in which the magnetization direction J 121  of the pinned layer  121  and the magnetization direction J 123  of the free layer  123  are orthogonal to each other. Concretely, first, while applying a magnetic field H 101  in the +X direction for example, the free layer  123  is formed by sputtering or the like and the direction AE 123  of the easy axis of magnetization is pinned (refer to  FIG. 24A ) and, after that, the intermediate layer  122  and the pinned layer  121  are sequentially formed. As shown in  FIG. 24B , while applying a magnetic field H 102  in the direction (for example, +Y direction) orthogonal to the magnetic field H 101 , annealing process is performed at a predetermined temperature (regularization heat treatment process). By the process, the magnetization directions J 121  and J 123  are aligned in the direction of the magnetic field H 102 . Further, as shown in  FIG. 24C , while applying a magnetic field H 103  of relatively low intensity in the direction (+X direction) orthogonal to the magnetic field H 102 , annealing process is performed at a rather low temperature (orthogonalization heat treatment process). By the processes, while the magnetization direction J 121  is pinned, only the magnetization direction J 123  is directed again to the +X direction. As a result, the stacked body  120  in which the magnetization directions J 121  and J 123  are orthogonal to each other is completed.  
      The GMR element having the spin valve structure subjected to the orthogonalization heat process is effective to obtain a high dynamic range as well as high output and is suitable for reproducing a magnetization inverted signal which is digitally recorded. Before such a GMR element is used, an AMR element using anisotropic magnet-resistive (AMR) effect was generally used as means for reproducing a digital recording signal. Hitherto, the AMR element is used as means for reproducing not only a digital signal but also an analog signal (refer to, for example, Translated National Publication of Paten Application No. Hei 9-508214). Recently, application of the GMR element as means for reproducing an analog signal in a manner similar to the AMR element has been being examined (refer to, for example, Japanese Patent Laid-Open No. 2001-358378).  
      In the case of applying the GMR element as the means for reproducing an analog signal, however, hysteresis of an output characteristic becomes a problem as described below. When the free layer  123  in the GMR element subjected to the orthogonalization heat treatment is observed from a microscopic viewpoint, as schematically shown in  FIG. 25 , it is found that spin directions  123 S in magnetic domains  123 D partitioned by magnetic walls  123 W are various and are not aligned in a predetermined direction. Such variations in the spin direction  123 S appear as hysteresis characteristic in the relation between the external magnetic field H and the electric resistance R when read current is passed in a state where an external magnetic field H is applied in a direction almost orthogonal to the spin direction  123 S.  FIG. 23  corresponds to an ideal state in which the spin directions in the magnetic domains in the free layer are perfectly aligned in one direction. In reality, however, the spin direction  123 S varies in the GMR element subjected to the orthogonalization heat treatment, so that a resistance change curve when the magnetic field H is applied in the direction orthogonal to the spin direction  123 S is expressed as HC 1  as shown in  FIG. 26 , and hysteresis occurs at the zero magnetic field. The occurrence of the hysteresis appears as 1/f noise in a relatively low frequency band as shown in  FIG. 27 . The 1/f noise occurs at a frequency “f” or lower and becomes more conspicuous as the frequency “f” becomes lower.  FIG. 27  shows a state where the influence of a 1/f noise component N 2  on “noise voltage density” increases as compared with a white noise component N 1  as the frequency “f” becomes lower. Increase in the 1/f noise is unpreferable since it is a big factor of deteriorating the reliability of the whole system.  
      In Japanese Patent Laid-Open No. 2001-358378, by disposing a plurality of soft magnetic bodies each having a linear or rectangular shape in parallel, the hysteresis is eliminated by using shape anisotropy. It is however difficult to completely eliminate the hysteresis, and the hysteresis occurs slightly. In addition, by narrowing the soft magnetic body as a sensor part, the shape anisotoropic magnetic field of the free layer increases, and it causes deterioration in sensitivity.  
     SUMMARY OF THE INVENTION  
      The present invention has been achieved in consideration of such problems and an object of the invention is to provide a magnetic sensing device capable of suppressing occurrence of hysteresis to thereby reduce 1/f noise, stably sensing a signal magnetic field at high sensitivity, and holding the stability even when a strong external magnetic field that disturbs a free layer is applied, and a method of forming the same.  
      A first magnetic sensing device of the invention has a stacked body including: a pinned layer having a magnetization direction pinned in a predetermined direction; a free layer whose magnetization direction changes according to an external magnetic field and, when the external magnetic field is zero, becomes parallel to the magnetization direction of the pinned layer; and an intermediate layer sandwiched between the pinned layer and the free layer. The intermediate layer has a thickness at which an exchange bias magnetic field in the magnetization direction of the pinned layer becomes positive. The exchange bias magnetic field is generated between the pinned layer and the free layer. In this case, preferably, the intermediate layer has a thickness in a range from 2.1 nm to 2.5 nm. The meaning of “parallel” in the specification includes not only a state where the magnetization directions of the pinned layer and the free layer are the same, that is, the angle formed between the magnetization direction of the pinned layer and that of the free layer is strictly 0° C. but also a state where a gradient caused by an error occurring in manufacture, variations in properties, and the like occurs. “The exchange bias magnetic field is positive” means that the directions of spins in the free layer are the same by using the direction of the spin in the pinned layer as a reference. “The same direction” in this case corresponds to the case where the angle formed between the direction of the spin in the pinned layer and that of the spin in the free layer lies in a range equal to or larger than 0° and less than 90°.  
      A second magnetic sensing device of the invention has a stacked body including: a pinned layer having a magnetization direction pinned in a predetermined direction; a free layer whose magnetization direction changes according to an external magnetic field and, when the external magnetic field is zero, becomes anti-parallel to the magnetization direction of the pinned layer; and an intermediate layer sandwiched between the pinned layer and the free layer. The intermediate layer has a thickness at which an exchange bias magnetic field in the magnetization direction of the pinned layer becomes negative. The exchange bias magnetic field is generated between the pinned layer and the free layer. In this case, preferably, the intermediate layer has a thickness in a range from 1.9 nm to 2.0 nm. The meaning of “anti-parallel” in the specification includes not only a state where the magnetization directions of the pinned layer and the free layer are opposite to each other, that is, the angle formed between the magnetization direction of the pinned layer and that of the free layer is strictly 180° C. but also a state where a gradient caused by an error occurring in manufacture, variations in properties, and the like occurs. “The exchange bias magnetic field is negative” means that the directions of spins in the free layer are opposite when the direction of the spin in the pinned layer is used as a reference. “The opposite direction” in this case corresponds to the case where the angle formed between the direction of the spin in the pinned layer and that of the spin in the free layer lies in a range larger than 90° and equal to or smaller than 180° 
      In the first and second magnetic sensing devices of the invention constructed as described above, as compared with the case where the magnetization directions of the pinned layer and the free layer are orthogonal to each other when the external magnetic field is zero, variations in the directions of spins in the magnetic domains in the free layer are reduced. Consequently, when read current is passed in a state where the external magnetic field is applied in the direction orthogonal to the magnetization direction of the pinned layer, occurrence of hysteresis in the relation between a change in the external magnetic field and the resistance change is suppressed, and stability of the free layer also improves. In particular, in the case where the direction of the easy axis of magnetization of the free layer is parallel to the magnetization direction of the pinned layer, the directions of spins in the magnetic domains are easily aligned and hyseresis is reduced more.  
      In the first and second magnetic sensing devices of the invention, preferably, the intermediate layer is made of copper. Each of the first and second magnetic sensing devices may have bias applying means which applies a bias magnetic field to the free layer in a direction orthogonal to the magnetization direction of the pinned layer. In this case, the bias applying means can be either a permanent magnet or a bias current line extending in the magnetization direction of the pinned layer.  
      A method of forming the first magnetic sensing device includes: a stacking step of forming a stacked body by sequentially forming a first ferromagnetic layer whose magnetization direction changes according to an external magnetic field, an intermediate layer, and a second ferromagnetic layer having coercive force larger than that of the first ferromagnetic layer; and a regularization step of making a regularization so that the magnetization directions of the first and second ferromagnetic layers become parallel to each other. The intermediate layer is formed so as to have a thickness at which an exchange bias magnetic field in the magnetization direction of the second ferromagnetic layer becomes positive. The exchange bias magnetic field is generated between the first and second ferromagnetic layers, and setting of the magnetization directions of the first and second ferromagnetic layers in an initial state where the external magnetic field is zero is completed by the regularization step. The “initial state” denotes a state where the external magnetic field having a specific direction does not exist and a state which is a reference at the time of sensing the external magnetic field.  
      A method of forming the second magnetic sensing device includes: a stacking step of forming a stacked body by sequentially forming a first ferromagnetic layer whose magnetization direction changes according to an external magnetic field, an intermediate layer, and a second ferromagnetic layer having coercive force larger than that of the first ferromagnetic layer; and a regularization step of making a regularization so that the magnetization directions of the first and second ferromagnetic layers become anti-parallel to each other. The intermediate layer is formed so as to have a thickness at which an exchange bias magnetic field in the magnetization direction of the second ferromagnetic layer becomes negative. The exchange bias magnetic field generated between the first and second ferromagnetic layers, and setting of the magnetization directions of the first and second ferromagnetic layers in an initial state where the external magnetic field is zero is completed by the regularization step.  
      In the methods of forming the first and second magnetic sensing devices according to the invention, the setting of the magnetization directions of the first and second ferromagnetic layers in the initial state where the external magnetic field is zero is completed by the regularization step. Consequently, as compared with the case where the first and second ferromagnetic layers have the magnetization directions which are orthogonal to each other, variations in the directions of spins in the magnetic domains in the first ferromagnetic layer are reduced. Therefore, the magnetic sensing device is obtained such that when read current is passed in a state where the external magnetic field is applied in the direction orthogonal to the magnetization direction of the second ferromagnetic layer, occurrence of hysteresis in the relation between a change in the external magnetic field and the resistance change is suppressed and stability of the free layer improves.  
      In the method of forming the first magnetic sensing device of the invention, preferably, the intermediate layer is formed so as to have a thickness in a range from 2.1 nm to 2.5 nm by using copper. When the first ferromagnetic layer is formed so as to have an easy axis of magnetization, and the regularization is made so that the magnetization directions of the first and second ferromagnetic layers become parallel to the easy axis of magnetization, variations in the directions of spins are further reduced.  
      In the method of forming the first magnetic sensing device according to the invention, when the regularization is made by performing an annealing process while applying a magnetic field in the same direction as the direction of the easy axis of magnetization, for example, at a temperature in a range from 250° C. to 400° C. while applying a magnetic field in a range from 1.6 kA/m to 160 kA/m, occurrence of hysteresis is further suppressed.  
      In the method of forming the second magnetic sensing device according to the invention, preferably, the intermediate layer is formed so as to have a thickness in a range from 1.9 nm to 2.0 nm. When the first ferromagnetic layer is formed so as to have an easy axis of magnetization, and the regularization is made so that the magnetization direction of the second ferromagnetic layer becomes parallel to the easy axis of magnetization, and the magnetization direction of the first ferromagnetic layer becomes anti-parallel to the easy axis of magnetization, variations in the directions of spins are further reduced.  
      In the method of forming the second magnetic sensing device according to the invention, in the regularization step, an annealing process is performed while applying a magnetic field in the same direction as the direction of the easy axis of magnetization, an annealing process is performed while applying a magnetic field in the direction opposite to the direction of the easy axis of magnetization, and an annealing process is performed while applying a magnetic field in the same direction as the direction of the easy axis of magnetization. In such a manner, occurrence of hysteresis is further suppressed.  
      The first magnetic sensing device of the invention has a stacked body including: a pinned layer having a magnetization direction pinned in a predetermined direction; a free layer whose magnetization direction changes according to an external magnetic field and, when the external magnetic field is zero, becomes parallel to the magnetization direction of the pinned layer; and an intermediate layer sandwiched between the pinned layer and the free layer. The intermediate layer has a thickness at which an exchange bias magnetic field in the magnetization direction of the pinned layer becomes positive. The exchange bias magnetic field is generated between the pinned layer and the free layer. Therefore, in the case of passing read current in a state where the external magnetic field is applied in the direction orthogonal to the magnetization direction of the pinned layer, occurrence of hysteresis in the relation between a change in the external magnetic field and the resistance change can be suppressed, and stability of the free layer also improves. Moreover, different from the case of using shape anisotropy, deterioration in sensitivity does not occur. As a result, 1/f noise is suppressed and a signal magnetic field can be stably sensed at high sensitivity. In particular, the value of the magnetic field intensity can be measured accurately and continuously, so that the invention can be sufficiently applied not only to a digital sensor but also to an analog sensor. In particular, when the free layer has the easy axis of magnetization parallel to the magnetization direction of the pinned layer, variations in the directions of spins in the free layer can be reduced. As a result, sensitivity and stability can be further improved.  
      The second magnetic sensing device of the invention has a stacked body including: a pinned layer having a magnetization direction pinned in a predetermined direction; a free layer whose magnetization direction changes according to an external magnetic field and, when the external magnetic field is zero, becomes anti-parallel to the magnetization direction of the pinned layer; and an intermediate layer sandwiched between the pinned layer and the free layer. The intermediate layer has a thickness at which an exchange bias magnetic field in the magnetization direction of the pinned layer becomes negative, the exchange bias magnetic field is generated between the pinned layer and the free layer. Consequently, in the case of passing read current in a state where the external magnetic field is applied in the direction orthogonal to the magnetization direction of the pinned layer, effects similar to those of the first magnetic sensing device of the invention are obtained.  
      When each of the first and second magnetic sensing devices of the invention has bias applying means which applies a bias magnetic field to the free layer in a direction orthogonal to the magnetization direction of the pinned layer, by applying the bias magnetic field of proper intensity, the resistance change of the read current with respect to the external magnetic field can be made linear. In the case where the bias applying means takes the form of a bias current line extending in the magnetization direction of the pinned layer, by determining the direction of passing the bias current, the direction of the bias magnetic field is also determined.  
      The method of forming the first magnetic sensing device of the invention includes: a stacking step of forming a stacked body by sequentially forming a first ferromagnetic layer whose magnetization direction changes according to an external magnetic field, an intermediate layer, and a second ferromagnetic layer having coercive force larger than that of the first ferromagnetic layer; and a regularization step of making a regularization so that the magnetization directions of the first and second ferromagnetic layers become parallel to each other. The intermediate layer is formed so as to have a thickness at which an exchange bias magnetic field in the magnetization direction of the second ferromagnetic layer becomes positive, the exchange bias magnetic field is generated between the first and second ferromagnetic layers, and setting of the magnetization directions of the first and second ferromagnetic layers in an initial state where the external magnetic field is zero is completed by the regularization step. Consequently, the magnetic sensing device can be obtained in which, in the case of passing read current in a state where the external magnetic field is applied in the direction orthogonal to the magnetization direction of the pinned layer, occurrence of hysteresis in the relation between a change in the external magnetic field and the resistance change can be suppressed, and stability of the free layer also improves. Moreover, different from the case of using shape anisotropy, deterioration in sensitivity does not occur. In particular, by forming the first ferromagnetic layer so as to have the easy axis of magnetization, making the regularization by performing the annealing process while applying the magnetic field in the same direction as the direction of the easy axis of magnetization, and setting the magnetization directions of the first and second ferromagnetic layers to be parallel to the easy axis of magnetization, variations in the spin directions can be further reduced. As a result, 1/f noise is suppressed and a signal magnetic field can be stably sensed at high sensitivity. In this case, the value of the magnetic field intensity itself can be measured accurately and continuously, so that the invention can be sufficiently applied not only to a digital sensor but also to an analog sensor. In particular, when the free layer has the easy axis of magnetization parallel to the magnetization direction of the pinned layer, variations in the directions of spins in the free layer can be reduced. As a result, sensitivity and stability can be further improved.  
      The method of forming the second magnetic sensing device of the invention includes: a stacking step of forming a stacked body by sequentially forming a first ferromagnetic layer whose magnetization direction changes according to an external magnetic field, an intermediate layer, and a second ferromagnetic layer having coercive force larger than that of the first ferromagnetic layer; and a regularization step of making a regularization so that the magnetization directions of the first and second ferromagnetic layers become anti-parallel to each other. The intermediate layer is formed so as to have a thickness at which an exchange bias magnetic field in the magnetization direction of the second ferromagnetic layer becomes negative, the exchange bias magnetic field is generated between the first and second ferromagnetic layers, and setting of the magnetization directions of the first and second ferromagnetic layers in an initial state where the external magnetic field is zero is completed by the regularization step. Consequently, the magnetic sensing device can be obtained in which, in the case of passing read current in a state where the external magnetic field is applied in the direction orthogonal to the magnetization direction of the pinned layer, occurrence of hysteresis in the relation between a change in the external magnetic field and the resistance change can be suppressed, and stability of the free layer also improves. Moreover, different from the case of using shape anisotropy, deterioration in sensitivity does not occur. In particular, when the regularization is made by sequentially performing the first step of performing the annealing process while applying the magnetic field in the same direction as the direction of the easy axis of magnetization of the first ferromagnetic layer, the second step of performing the annealing process while applying the magnetic field in the direction opposite to the direction of the easy axis of magnetization, and the third step of performing the annealing process while applying the magnetic field in the same direction as that of the easy axis of magnetization, the magnetization direction of the second ferromagnetic layer is set to be parallel to the easy axis of magnetization, and the magnetization direction of the first ferromagnetic layer is set to be anti-parallel to the easy axis of magnetization, variations in the spin directions can be further reduced. Therefore, effects similar to those of the method of forming the first magnetic sensing device of the invention can be obtained.  
      Other and further objects, features and advantages of the invention will appear more fully from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIGS. 1A  to  1 C are schematic diagrams showing the configuration of a magnetic sensing device according to a first embodiment of the invention.  
       FIG. 2  is an exploded perspective view showing a stacked body as a component of the magnetic sensing device illustrated in  FIGS. 1A  to  1 C.  
       FIG. 3  is a conceptual diagram showing the relation between the thickness of an intermediate layer in the stacked body shown in  FIG. 2  and the spin direction of a free layer.  
       FIG. 4  is a characteristic diagram showing the relation between the thickness of the intermediate layer in the stacked body shown in  FIG. 2  and an exchange bias magnetic field.  
       FIG. 5  is a perspective view showing a detailed configuration of a part of the stacked body illustrated in  FIG. 2 .  
       FIG. 6  is a perspective view showing a more detailed configuration of the part of the stacked body illustrated in  FIG. 2 .  
       FIG. 7  is a perspective view showing a detailed configuration of another part of the stacked body illustrated in  FIG. 2 .  
       FIG. 8  is a conceptual diagram schematically showing a spin direction distribution in a free layer of the stacked body illustrated in  FIG. 2 .  
       FIG. 9  is a characteristic diagram showing magnetic field dependency of a resistance change rate in the magnetic sensing device illustrated in  FIGS. 1A  to  1 C.  
       FIGS. 10A and 10B  are conceptual diagrams showing a process of forming the magnetic sensing device illustrated in  FIGS. 1A  to  1 C.  
       FIG. 11  is a schematic diagram showing the configuration of a magnetic sensing device according to a second embodiment of the invention.  
       FIG. 12  is a characteristic diagram showing magnetic field dependency of a resistance change rate in the magnetic sensing device illustrated in  FIG. 11 .  
       FIGS. 13A  to  13 D are conceptual diagrams showing a process of forming the magnetic sensing device illustrated in  FIG. 11 .  
       FIGS. 14A  to  14 F are characteristic diagrams showing the relation between characteristics and the thickness of an intermediate layer in the magnetic sensing device illustrated in  FIGS. 1A  to  1 C.  
       FIGS. 15A  to  15 C are characteristic diagrams showing magnetic field dependency of a resistance change rate in the magnetic sensing device illustrated in  FIGS. 1A  to  1 C.  
       FIGS. 16A  to  16 D are other characteristic diagrams showing magnetic field dependency of a resistance change rate in the magnetic sensing device illustrated in  FIGS. 1A  to  1 C.  
       FIG. 17  is an exploded perspective view showing the configuration of a conventional stacked body having a spin valve structure.  
       FIG. 18  is a perspective view showing a detailed configuration of a part of the stacked body illustrated in  FIG. 17 .  
       FIG. 19  is a perspective view showing a more detailed configuration of a part of the stacked body illustrated in  FIG. 17 .  
       FIG. 20  is a perspective view showing a detailed configuration of another part of the stacked body illustrated in  FIG. 17 .  
       FIGS. 21A and 21B  are diagrams for explaining the action of a general GMR effect.  
       FIGS. 22A  to  22 C are diagrams for explaining the operation of a thin film magnetic head in which the stacked body shown in  FIG. 17  is mounted.  
       FIG. 23  is a characteristic diagram showing the relation between an external magnetic field (signal magnetic field) and electric resistance in the stacked body illustrated in  FIG. 17 .  
       FIGS. 24A  to  24 C are conceptual diagrams showing a process of forming the stacked body illustrated in  FIG. 17 .  
       FIG. 25  is a conceptual diagram schematically showing a spin direction distribution in the free layer of the stacked body illustrated in  FIG. 17 .  
       FIG. 26  is a characteristic diagram showing magnetic field dependency of resistance change in the stacked body illustrated in  FIG. 17 .  
       FIG. 27  is a characteristic diagram showing frequency dependency of noise which occurs in the stacked body illustrated in  FIG. 17 . 
    
    
     DETAILED DESCRIPTION OF THE PRFERRED EMBODIMENTS  
      Embodiments of the invention will now be described in detail hereinbelow with reference to the drawings.  
     First Embodiment  
      First, the configuration of a magnetic sensing device as a first embodiment of the invention will be described with reference to  FIGS. 1A  to  1 C to  FIG. 7 .  
       FIGS. 1A  to  1 C show a schematic configuration of a magnetic sensing device  10  of the first embodiment.  FIG. 1A  is a plan view showing the configuration of the magnetic sensing device  10  and  FIG. 1B  shows a sectional configuration of the magnetic sensing device  10 , taken along the line IB-IB of  FIG. 1A .  FIG. 1C  shows an equivalent circuit corresponding to  FIG. 1A . The magnetic sensing device  10  senses the presence/absence of a magnetic field in the environment of the magnetic sensing device  10  (external magnetic field) and the intensity of the magnetic field.  
      As shown in  FIG. 1A , in the magnetic sensing device  10 , a stacked body  20  and a bias current line  30  as bias applying means provided adjacent to the stacked body  20  are formed on a not-shown substrate. The stacked body  20  has a pinned layer whose magnetization direction is pinned in a predetermined direction (+Y direction in  FIG. 1A ) as will be described in detail later. The bias current line  30  is disposed so as to extend in the magnetization direction of the pinned layer near the stacked body  20  and bias current  31  flows. As shown in  FIGS. 1A and 1B , the bias current  31  can be passed in the direction of the arrow (+Y direction around the stacked body  20 ) or the opposite direction (−Y direction around the stacked body  20 ). The bias current line  30  is electrically insulated from the stacked body  20 . Separately from the bias current line  30 , a lead wire is connected to the stacked body  20  and read current can be passed between terminals T 1  and T 2 . In this case, the stacked body  20  can be regarded as a resistor, so that the magnetic sensing device  10  is an equivalent circuit as shown in  FIG. 1C .  
      The stacked body  20  is obtained by stacking a plurality of functional films including a magnetic layer and, as shown in  FIG. 2 , includes a pinned layer  21  having a magnetization direction J 21  pinned to a predetermined direction (for example, Y direction in  FIG. 2 ), a free layer  23  having a magnetization direction J 23  which changes according to the external magnetic field H, and an intermediate layer  22  sandwiched between the pinned layer  21  and the free layer  23  and having no specific magnetization direction. The intermediate layer  22  is made of copper (Cu) and whose top and under faces are in contact with the pinned layer and the free layer  23 , respectively. The intermediate layer  22  can be made of a nonmagnetic metal having high conductivity such as copper or gold (Au).  FIG. 2  shows an initial state where the external magnetic field H is zero (H=0) and the magnetization direction J 23  is parallel to the magnetization direction J 21 . Each of the top face (the face on the side opposite to the intermediate layer  22 ) of the pinned layer  21  and the under face (the face on the side opposite to the intermediate layer  22 ) of the free layer  23  is protected with a not-shown protection layer.  
      An exchange bias magnetic field Hin in the magnetization direction J 21  is generated between the pinned layer  21  and the free layer  23  (hereinbelow, simply called “exchange bias magnetic field Hin”), and the pinned layer  21  and the free layer  23  act each other via the intermediate layer  22 . The intensity of the exchange bias magnetic field Hin changes with the spin direction of the free layer  23  in accordance with the interval between the pinned layer  21  and the free layer  23  (that is, the thickness “t” of the intermediate layer  22 ). In the embodiment, the intermediate layer  22  has the thickness “t” in a range in which the exchange bias magnetic field Hin becomes positive. The thickness “t” is desirably within the range from 2.1 nm to 2.5 nm. The thickness “t” exceeding 2.5 nm is not preferable because the resistance change rate sharply deteriorates. The stacked body  20  is a GMR element having the spin valve structure. When the external magnetic field H is applied, the relative angle between the magnetization direction J 23  of the free layer  23  and the magnetization direction J 21  of the pinned layer  21  changes. The relative angle varies according to the magnitude and direction of the external magnetic field H. Although  FIG. 2  shows an example of the configuration in which the free layer  23 , intermediate layer  22 , and pinned layer  21  are stacked in order from the bottom, the invention is not limited to the configuration and the layers may be stacked in reverse order.  
       FIG. 3  shows the relation between the thickness “t” (horizontal axis) and the exchange bias magnetic field Hin (vertical axis).  FIG. 4  schematically shows the relation between the thickness “t” and change in the spin direction SP 23  of the free layer  23  with respect to the spin direction SP 21  of the pinned layer  21 . Reference numerals t 0  to t 8  in  FIG. 4  correspond to those of  FIG. 3 .  
      As the thickness “t” increases, the exchange bias magnetic field Hin repeats increase and decrease and is gradually converged to zero (Hin=0). The thickness “t” of 0 (t=t 0 ) corresponds to the state where the pinned layer  21  and the free layer  23  are in perfect contact with each other (state where the intermediate layer  22  does not exist). In this case, the pinned layer  21  and the free layer  23  are integrated, so that the spin directions SP 21  and SP 23  are the same, and the exchange bias magnetic field Hin is zero (Hin=0). When the pinned layer  21  and the free layer  23  are slightly apart from each other via the intermediate layer  22  and the thickness “t” of the intermediate layer  22  becomes thickness t 1  (for example, about 0.1 to 1.0 nm) larger than a magnetic quantum size ts, the spin direction SP 23  slightly turns and forms an angle of, for example, 45° with respect to the spin direction SP 21 . In this case, the exchange bias magnetic field Hin is positive (Hin&gt;0). Further, when the thickness “t” increases like t 2 , t 3 , and t 4  in order, the spin direction SP 23  turns more, and the exchange bias magnetic field Hin gradually decreases. At the thickness t=t 2  when the spin direction SP 23  is orthogonal to the spin direction SP 21 , the exchange bias magnetic field Hin is zero (Hin=0). At the thickness t=t 3  when the angle of, for example, 135° is formed with respect to the spin direction SP 21 , the exchange bias magnetic field Hin is negative (Hin&lt;0). At the thickness t=t 4  at which the exchange bias magnetic field Hin is the minimum value, the spin direction SP 23  is stabilized in a state where it is inverted from the initial state.  
      Further, as the thickness t increases like t 5 , t 6 , t 7 , and t 8  in order, the spin direction SP 23  turns more, and the exchange bias magnetic field Hin gradually increases. At the thickness t=t 6  when the spin direction SP 23  is orthogonal to the spin direction SP 21  (forms the angle of 270°), the exchange bias magnetic field Hin is zero (Hin=0). At the thickness t=t 7  at which the angle of 315° is formed with respect to the spin direction SP 21 , the exchange bias magnetic field Hin is positive (Hin&gt;0). At the thickness t=t 8  at which the exchange bias magnetic field Hin is the maximum value, the spin direction SP 23  becomes parallel to the spin direction SP 21  and is stabilized. The present embodiment corresponds to this state.  
       FIG. 5  shows a detailed configuration of the pinned layer  21 . The pinned layer  21  has a configuration in which a magnetization pinned film  24  and an antiferromagnetic film  25  are stacked in order from the side of the intermediate layer  22 . The magnetization pinned film  24  is made of a ferromagnetic material such as cobalt (Co), cobalt iron alloy (CoFe) or the like. The magnetization direction of the magnetization pinned layer  24  is the magnetization direction J 21  of the pinned layer  21  as a whole. The antiferromagnetic film  25  is made of an antiferromagnetic material such as platinum manganese alloy (PtMn) or iridium manganese alloy (IrMn). The antiferromagnetic film  25  is in a state where the spin magnetic moment in a predetermined direction (for example, the +Y direction) and the spin magnetic moment in the opposite direction (for example, the −Y direction) completely cancel out each other, and functions so as to pin the magnetization direction J 21  of the magnetization pinned film  24 . A protection film  26  is made of a non-magnetic material which is chemically stable such as tantalum (Ta) or hafnium (Hf) and is to protect the magnetization pinned film  24 , antiferromagnetic film  25 , and the like.  
      The magnetization pinned film  24  may have a single layer structure or a configuration in which a first ferromagnetic film  241 , an exchange coupling film  242 , and a second ferromagnetic film  243  are stacked in order from the side of the intermediate layer  22  as shown in  FIG. 6 . The stacked body  20  including the pinned layer  21  and having the configuration of  FIG. 6  is called a synthetic spin valve structure. The first and second ferromagnetic films  241  and  243  are made of a ferromagnetic material such as cobalt, CoFe or the like and the exchange coupling film  242  is made of a non-magnetic material such as ruthenium (Ru). In this case, the first and second ferromagnetic films  241  and  243  are exchange-coupled via the exchange coupling film  242  so that their magnetization directions become opposite to each other. Consequently, the magnetization direction of the magnetization pinned film  24  as a whole is stabilized. Further, a leakage magnetic field which leaks from the magnetization pinned film  24  to the free layer  23  can be weakened.  
      The free layer  23  may have a single-layer structure or a configuration in which two ferromagnetic thin films  231  and  233  are exchange-coupled to each other via an intermediate film  232  as shown in  FIG. 7 . In this case, the coercive force in the axis of hard magnetization of the free layer  23  can be further decreased.  
      The bias current line  30  is made of a metal material having high conductivity such as copper (Cu), gold (Au), or the like and functions so as to apply a bias magnetic field Hb to the stacked body  20 .  
      The action of the magnetic sensing device  10  having the above configuration will now be described.  
      Different from the magnetization pinned film  24 , the magnetization direction J 23  of the free layer  23  turns according to the magnitude and direction of the external magnetic field H. The axis AE 23  of easy magnetization of the free layer  23  is parallel to the magnetization direction J 21  of the pinned layer  21 . Therefore, in the stacked body  20 , when the external magnetic field H is zero (that is, the initial state shown in  FIG. 2 ), all of the axis AE 23  of easy magnetization of the free layer  23  and the magnetization directions J 23  and J 21  are parallel to each other. Consequently, when the external magnetic field H is zero, the spin directions in the free layer  23  are easily aligned in a predetermined direction.  FIG. 8  is a conceptual diagram schematically showing spin directions in magnetic domains in the free layer  23  in the case where the external magnetic field H is zero. As shown in  FIG. 8 , the free layer  23  has a plurality of magnetic domains  23 D partitioned by magnetic domain walls  23 W, and spins  23 S are almost aligned in the same direction (magnetization direction J 23 ).  
      As described above, the stacked body  20  including the free layer  23  in which the spin directions are aligned hardly displays hysteresis when the external magnetic field H is applied in the direction orthogonal to the magnetization direction J 21  (the magnetization direction J 23 ).  FIG. 9  shows the relation between the external magnetic field H and resistance change rate ΔR/R. The relation is expressed by an almost one curve C 1  which is bilaterally symmetrical and shows the minimum value (ΔR/R=0) at the external magnetic field H=0. Consequently, when sensing (detection) of an external magnetic field in a direction orthogonal to the magnetization direction J 21  is executed by using the magnetic sensing device  10 , occurrence of hysteresis caused by inversion of the magnetization direction J 23  of the free layer  23  is suppressed, and 1/f noise is reduced.  
      In the case of performing the sensing by using the magnetic sensing device  10  of the embodiment, as shown in  FIGS. 1A and 1B , the bias magnetic field Hb is applied to the stacked body  20  by using the bias current line  30 . Concretely, by passing the bias current  31  in, for example, the +Y direction to the bias current line  30 , the bias magnetic field Hb in the +X direction is generated for the stacked body  20 . Both of the magnetization directions J 21  and J 23  are set so as to be the +Y direction and are orthogonal to the bias magnetic field Hb. The reason why the bias magnetic field Hb is applied is because the curve C 1  is non-linear around the external magnetic field H=0 as shown in  FIG. 7 . To detect a change in the external magnetic field H with high precision, it is desirable to use the characteristics of two linear zones L 1  and L 2  corresponding to inclined face portions on both sides of the curve C 1 . Therefore, it is necessary to apply the bias magnetic field Hb of the magnitude corresponding to a bias point BP 1  or BP 2  in an initial state. The bias points BP 1  and BP 2  are positioned in the center of the linear zones L 1  and L 2 , respectively, and in positions indicative of the resistance change rates ΔR/R which are equal to each other.  
      For example, when the magnetic field H in the +X direction is defined as a positive field in  FIG. 1A , it is preferable to pass the bias current  31  in the +Y direction to generate the bias magnetic field Hb (BP 1 ) corresponding to the bias point BP 1 . When the external magnetic field H+in the positive direction (+X direction) is applied in this state, as obvious from the curve C 1  of  FIG. 9 , the resistance change rate ΔR/R of the stacked body  20  becomes higher (than that in the initial state). On the contrary, when the external magnetic field H− in the negative direction (−X direction) is applied in the initial state where the bias magnetic field Hb (BP 1 ) is applied, the resistance change rate ΔR/R of the stacked body  20  becomes lower (than that in the initial state). In the case where the bias magnetic field Hb (BP 2 ) corresponding to the bias point BP 2  is generated by passing the bias current  31  in the −Y direction, when the external magnetic field H+in the positive direction (+X direction) is applied, the resistance change rate ΔR/R becomes lower (than that in the initial state). When the external magnetic field H− in the negative direction (−X direction) is applied, the resistance change rate ΔR/R becomes higher (than that in the initial state). As described above, in any of the cases, the direction of the external magnetic field H can be known from the direction of change in the resistance change rate ΔR/R and, moreover, the magnitude of the external magnetic field H can be known from the magnitude of the change in the resistance change rate ΔR/R. Without the bias applying means, the sensing can be performed. However, when the linear zones L 1  and L 2  are used with the bias applying means, sensing can be performed with higher precision.  
      A method of forming the magnetic sensing device  10  will now be described in detail hereinbelow with reference to  FIG. 2  and  FIGS. 10A and 10B .  FIGS. 10A and 10B  are conceptual diagrams showing a simplified process of forming the magnetic sensing device  10 .  
      In the method of forming the magnetic sensing device  10  of the embodiment, first, a first ferromagnetic layer (as the free layer  23 ) is formed on a not-shown substrate by sputtering or the like by using a soft magnetic material such as NiFe. At this time, the direction AE 23  of the easy axis of magnetization is determined by forming the film while applying a magnetic field H 1  in a predetermined position (for example, the +Y direction) (refer to  FIG. 10A ). The intermediate layer  22  is formed by using a non-magnetic metal material such as copper and a second ferromagnetic film (which will become the pinned layer  21 ) is formed by using a material having a coercive force larger than that of the first ferromagnetic film (stacking process). After that, a regularization is made so that the magnetization direction J 23  of the first ferromagnetic layer and the magnetization direction J 21  of the second ferromagnetic layer correspond to the direction AE 23  of the easy axis of magnetization (a regularization process). Concretely, while applying the magnetic field H 2  having intensity in a range from 1.6 kA/m to 160 kA/m in the same direction as the direction AE 23  of the easy axis of magnetization, annealing process is performed at a temperature in a range from 250° C. to 400° C. (preferably 270° C.) for about four hours. By the process, the pinned layer  21  having the magnetization direction J 21  pinned in a predetermined direction (+Y direction) is formed, and the free layer  23  having the direction AE 23  of the easy axis of magnetization which is the same as the magnetization direction J 21  and the magnetization direction J 23  is formed. By the regularization process, setting of the magnetization directions J 21  and J 23  of the pinned layer  21  and the free layer  23  in the initial state where the external magnetic field H is zero is completed. In such a manner, formation of the stacked body  20  in which the free layer  23 , intermediate layer  22 , and pinned layer  21  are sequentially formed on the substrate is completed. After that, by performing predetermined processes such as a process of forming the bias current line  30  via an insulating layer and a process of connecting a lead wire for passing read current, the magnetic sensing device  10  is completed.  
      As described above, in the magnetic sensing device  10  and the method of forming the same of the embodiment, the stacked body  20  is provided which includes the pinned layer  21  having the magnetization direction J 21  pinned to a predetermined direction (Y direction), the free layer  23  having the magnetization direction J 23  which changes according to the external magnetic field H and is parallel to the magnetization direction J 21  when the external magnetic field H is zero, and the intermediate layer  22  sandwiched between the pinned layer  21  and the free layer  23 . Since the thickness “t” of the intermediate layer  22  is set so that the exchange bias magnetic field Hin becomes positive, the magnetization direction J 23  is not inverted by the external magnetic field from a direction orthogonal to the magnetization direction J 21 . Thus, the magnetization directions J 21  and J 23  are stabilized. Therefore, in the case of passing read current in a state where the external magnetic field H is applied in the direction orthogonal to the magnetization direction J 21  (magnetization direction J 23 ), occurrence of hysteresis due to inversion of the magnetization direction J 23  in the relation between the change in the external magnetic field H and the resistance change R can be suppressed. As a result, 1/f noise is suppressed and a signal magnetic field can be stably sensed at high sensitivity. In particular, the value of the magnetic field intensity can be measured accurately and continuously, so that the magnetic sensor is suitable as an analog sensor such as an ammeter.  
     Second Embodiment  
      Referring now to  FIG. 11 , the magnetic sensing device  10  as a second embodiment will be described.  
      The magnetic sensing device  10  of the second embodiment has a configuration similar to that of the first embodiment except that the magnetization direction of the free layer  23  in the stacked body  20  is different from that of the first embodiment. Consequently, parts overlapping those in the first embodiment will not be described in the second embodiment.  
      The stacked body  20  of the second embodiment includes, as shown in  FIG. 11 , the free layer  23  having the magnetization direction J 23 A which is anti-parallel to the magnetization direction J 21  of the pinned layer  21  in the initial state where the external magnetic field H is zero (H=0). The thickness “t” of the intermediate layer  22  is preferably in a range from 1.9 nm to 2.0 nm and, more preferably, 1.9 nm.  
      The exchange bias magnetic field Hin is generated between the pinned layer  21  and the free layer  23  and its intensity is negative. That is, this state corresponds to the state where the thickness “t” of the intermediate layer  22  is equal to t 4  in  FIGS. 3 and 4 .  
      The stacked body  20  having such a configuration hardly displays hysteresis when the external magnetic field H is applied in the direction orthogonal to the magnetization direction J 21  as shown in  FIG. 12 .  FIG. 12  shows the relation between the external magnetic field H and resistance change rate ΔR/R. The relation is expressed by an almost one curve C 2  which is bilaterally symmetrical and shows the maximum value (ΔR/R=0) at the external magnetic field H=0. Consequently, when sensing (detection) of an external magnetic field in a direction orthogonal to the magnetization direction J 21  is executed by using the magnetic sensing device  10 , occurrence of hysteresis caused by inversion of the magnetization direction J 23 A is suppressed, and 1/f noise is reduced.  
      In the case of performing the sensing by using the magnetic sensing device  10  of the second embodiment, in a manner similar to the first embodiment, as shown in  FIGS. 1A and 1B , it is desirable to apply the bias magnetic field Hb to the stacked body  20  by using the bias current line  30  to detect a change in the external magnetic field H with high precision by using the characteristics of two linear zones L 3  and L 4  corresponding to inclined portions on both sides in the curve C 2 .  
      A method of forming the magnetic sensing device  10  will now be described in detail hereinbelow with reference to  FIG. 11  and  FIGS. 13A  to  13 D.  FIGS. 13A  to  13 D are conceptual diagrams showing a simplified process of forming a magnetic sensing device  10 .  
      In the method of forming the magnetic sensing device  10  of the embodiment, first, a first ferromagnetic layer as the free layer  23  is formed on a not-shown substrate. At this time, the direction AE 23  of the easy axis of magnetization is determined by forming the film while applying a magnetic field H 1  in a predetermined position (for example, the +Y direction) (refer to  FIG. 13A ). Next, the intermediate layer  22  is formed and a second ferromagnetic film which will become the pinned layer  21  is formed (stacking process). After that, a regularization is made so that the magnetization direction J 21  of the second ferromagnetic layer is the same as the direction AE 23  of the easy axis of magnetization and the magnetization direction J 23 A of the first ferromagnetic layer becomes the opposite to the direction AE 23  (regularization process). Concretely, while applying the magnetic field H 2  having intensity in a range from 1.6 kA/m to 160 kA/m in the same direction (+Y direction) as the direction AE 23  of the easy axis of magnetization, annealing process is performed at a temperature in a range from 250° C. to 400° C. (preferably, 270° C.) for about four hours (first annealing process). Next, while applying a magnetic field H 3  having intensity in a range from 1.6 kA/m to 160 kA/m in the direction (−Y direction) opposite to the direction AE 23  of the easy axis of magnetization, annealing process is performed at a temperature in a range from 250° C. to 400° C. (preferably, 270° C.) for about one hour (second annealing process). Further, while applying a magnetic field H 4  having intensity in a range from 1.6 kA/m to 160 kA/m in the same direction (+Y direction) as the direction AE 23  of the easy axis of magnetization, annealing process is performed at a temperature in a range from 250° C. to 400° C. (preferably, 270° C.) for about one hour (third annealing process). By the processes, the pinned layer  21  having the magnetization direction J 21  pinned in a predetermined direction (+Y direction) is formed, and the free layer  23  having the direction AE 23  of the easy axis of magnetization which is opposite to the magnetization direction J 21  is formed. As described above, the magnetization directions J 21  and J 23 A are stabilized so as to be opposite to each other. That is, by the regularization process including the first to third annealing processes, setting of the magnetization directions J 21  and J 23 A of the pinned layer  21  and the free layer  23  in the initial state where the external magnetic field H is zero is completed. In such a manner, formation of the stacked body  20  in which the free layer  23 , intermediate layer  22 , and pinned layer  21  are sequentially formed on the substrate is completed. After that, by performing predetermined processes similar to those of the first embodiment, the magnetic sensing device  10  is completed. Although the regularization can be performed to a certain degree without performing the second and third annealing processes, the regularization is promoted more by performing the first to third annealing processes as described above. Thus, occurrence of hysteresis can be further reduced.  
      As described above, in the magnetic sensing device  10  and the method of forming the same of the embodiment, the stacked body  20  is provided which includes the pinned layer  21  having the magnetization direction J 21  pinned to a predetermined direction (Y direction), the free layer  23  having the magnetization direction J 23 A which changes according to the external magnetic field H and is anti-parallel to the magnetization direction J 21  when the external magnetic field H is zero, and the intermediate layer  22  sandwiched between the pinned layer  21  and the free layer  23 . Since the thickness “t” of the intermediate layer  22  is set so that the exchange bias magnetic field Hin becomes negative, the magnetization directions J 21  and J 23 A are stabilized opposite to each other, and the magnetization direction J 23 A is not inverted by the external magnetic field from a direction orthogonal to the magnetization direction J 21 . Thus, the magnetization directions J 21  and J 23 A are stabilized. Therefore, in the case of passing read current in a state where the external magnetic field H is applied in the direction orthogonal to the magnetization direction J 21  (magnetization direction J 23 A), occurrence of hysteresis due to inversion of the magnetization direction J 23 A in the relation between the change in the external magnetic field H and the resistance change R can be suppressed. As a result, effects similar to those of the first embodiment can be obtained.  
     EXAMPLE  
      An example of concrete numerical values of the magnetic sensing device  10  of the first embodiment will now be described.  
      In the example, the magnetic sensing device  10  having the stacked body  20  with the following configuration was formed on the basis of the magnetic sensing device forming method in the first and second embodiments. The stacked body  20  has the configuration of “0.3 of nickel iron alloy (NiFe), 1.0 of cobalt iron alloy (CoFe), copper (Cu), 2.5 of CoFe, 0.8 of ruthenium (Ru), 1.5 of CoFe, 15.0 of platinum manganese alloy (PtMn), and 3.0 of tantalum (Ta)”. “0.3 of NiFe and 1.0 of CoFe” corresponds to the free layer  23  having a bilayer structure. “Copper” corresponds to the intermediate layer  22 . “2.5 of CoFe, 0.8 of Ru, 1.5 of CoFe” corresponds to the magnetization pinned film  24  having a three-layer structure. “15.0 of PtMn” corresponds to the antiferromagnetic film  25 . “3.0 of tantalum” corresponds to he projection film. The numerical values indicated with the material names are thicknesses (nm) of the layers. In the example, by changing the thickness of the intermediate layer  22 , either the magnetization direction J 23  or J 23 A is selected in the free layer  23 .  
       FIGS. 14A  to  14 F show dependency on the thickness “t” of the intermediate layer  22  of the characteristics of the stacked body  20 .  FIG. 14A  shows a change in the exchange bias magnetic field (Hin) with the thickness “t”. As shown in  FIG. 14A , the exchange bias magnetic field Hin gradually decreases from the thickness t=1.6 nm and is negative in the range of 1.80 nm&lt;t&lt;2.1 nm. After that, when the thickness “t” further increases, the exchange bias magnetic field Hin gently increases and becomes positive. Therefore, in the range where the thickness “t” is larger than 1.8 nm and less than 2.0 nm, the state corresponds to the second embodiment in which the free layer  23  expresses the magnetization direction J 23 A. In the range where the thickness “t” is equal to or larger than 2.1 nm, the state corresponds to the first embodiment in which the free layer  23  has the magnetization direction J 23 .  
       FIG. 14B  shows a change in the coercive force Hc with respect to the thickness “t”. As shown in  FIG. 14B , the coercive force Hc is 2×10 3 /(4π) [A/m] at the thickness t=1.6 nm and gradually decreases to the thickness t=2.6 nm.  
       FIG. 14C  shows a change in an anisotropic magnetic field Hk with respect to the thickness “t”. As shown in  FIG. 14C , the coercive force Hc decreases rather sharply from the thickness t=1.6 nm to t=1.8 nm and, after that, as the thickness t increases, decreases gently.  
       FIG. 14D  shows a change in the resistance change rate ΔR/R with respect to the thickness “t”. As shown in  FIG. 14D , the resistance change rate ΔR/R decreases gently in a zone of around 12% at the thickness t of 1.6 nm to 2.5 nm. At the thickness t=2.6, the resistance change rate ΔR/R decreases sharply and drops to 8%.  
       FIGS. 14E and 14F  show changes in the resistance change amount (ΔRs) and sheet resistance (Rs) with respect to the thickness “t”, respectively. Both of them monotonously decrease at the thickness t=1.6 nm to 2.6 nm.  
       FIGS. 15A  to  15 C and  FIGS. 16A  to  16 D show the result of examination of dependency on the magnetic field of the resistive change rate ΔR/R in the stacked body  20 .  
       FIGS. 15A  to  15 C show changes in the resistance change rate ΔR/R of the case where the external magnetic field H is applied in the direction parallel with the magnetization direction J 21  of the pinned layer  21  in the stacked body. In this case, the thickness “t” of the intermediate layer  22  is 1.5 nm, and the exchange bias magnetic field Hin between the pinned layer  21  and the free layer  23  is positive.  FIG. 15A  is a characteristic diagram of the stacked body  20  of a rectangular shape in plan view having a width of 2 μm and a length of 180 μm.  FIG. 15B  is a characteristic diagram of the stacked body  20  of a rectangular shape in plan view having a width of 18 μm and a length of 180 μm.  FIG. 15C  is a characteristic diagram of the conventional stacked body  120  shown in  FIG. 17  when the external magnetic field H is applied in the direction orthogonal to the magnetization direction J 121 . The numbers (1) to (4) shown in  FIGS. 15A  to  15 C indicate the directions of change.  
      As obvious from  FIGS. 15A  to  15 C, the curve in the case where the external magnetic field H is applied to the positive side (the same direction as the magnetization direction J 21 ) and that in the case where the external magnetic field H is applied to the negative side (the same direction as that magnetization direction J 21 ) do not coincide with each other, and hysteresis appears.  
      On the other hand,  FIGS. 16A  to  16 D show changes in the resistance change rate ΔR/R in the case where the external magnetic field H is applied in the direction orthogonal to the magnetization direction J 21  of the pinned layer  21  in the stacked body  20 .  FIG. 16A  is a characteristic diagram of the stacked body  20  of a rectangular shape in plan view having a width of 2 μm and a length of 180 μm in a manner similar to  FIG. 15A .  FIG. 16B  is a characteristic diagram of the stacked body  20  of a rectangular shape in plan view having a width of 18 μm and a length of 180 μm in a manner similar to  FIG. 15B .  FIGS. 16C and 16D  are characteristic diagrams of the conventional stacked body  120  shown in  FIG. 17  when the external magnetic field H is applied in the direction orthogonal to the magnetization direction J 121 .  FIG. 16C  is a characteristic diagram of the stacked body  120  of a rectangular shape in plan view having a width of 18 μm and a length of 180 μm. The numbers (1) to (4) shown in  FIG. 16C  indicate the directions of change.  FIG. 16D  is a characteristic diagram of the stacked body  120  of a rectangular shape in plan view having a width of 2 μm and a length of 180 μm.  
      As obvious from  FIGS. 16A and 16B , the stacked body  20  of the invention exhibits the excellent resistance change rate ΔR/R at which hysteresis hardly occurs. In particular, in the case where the width is set to 18 μm ( FIG. 16B ), higher sensitivity (tilt of the curve) as compared with the case where the width is set to 2 μm ( FIG. 16A ) is obtained. In contrast, in the conventional stacked body  120 , by narrowing the width to 2 μm to increase the shape anisotoropy, occurrence of hysteresis is suppressed to a certain extent ( FIG. 16D ). However, the hysteresis could not be prevented and is slightly larger than that of the stacked body  20  of the invention shown in  FIG. 16B .  
      As described above, in the example, the thickness of the intermediate layer  22  is set so that the exchange bias magnetic field Hin becomes positive, so that the magnetization directions J 21  and J 23  are stabilized in the same direction. It was recognized that, in a state where the external magnetic field H is applied in the direction orthogonal to the magnetization direction J 21 , occurrence of the hysteresis in the relation between a change in the external magnetic field H and the resistance change R (resistance change rate ΔR/R) can be suppressed.  
      Although the invention has been described above by some embodiments, the invention is not limited to the embodiments but may be variously modified. For example, although the case of sensing the analog signal magnetic field generated by the current flowing in a conductor has been described in the embodiments, the invention is not limited to the embodiments. The magnetic sensing device of the invention can be also applied for sensing a digital signal magnetic field of a high duty ratio like a magnetic encoder.  
      The magnetic sensing device of the invention can be used for the purpose of sensing a current value itself like an ammeter and also for an eddy current inspection technique of conducting a test for a defect in printing wiring or the like. In an application example, a line sensor in which a number of magnetic sensing devices are arranged on a straight line is formed and a change in eddy current is detected as a change in magnetic flux.  
      Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.