Abstract:
An in-stack bias is provided for stabilizing the free layer of a ballistic magneto resistive (BMR) sensor. In-stack bias includes a decoupling layer that is a spacer between the free layer and a ferromagnetic stabilizer layer of the in-stack bias, and an anti-ferromagnetic layer positioned above the ferromagnetic layer. The spacer is a nano-contact layer having magnetic particles positioned in a non-magnetic matrix. The free layer may be single layer, composed or synthetic, and the in-stack bias may be laterally bounded by the sidewalls, or alternatively, extend above the sidewalls and spacer. Additionally, a hard bias may also be provided. The spacer of the in-stack bias results in the reduction of the exchange coupling between the free layer and ferromagnetic stabilizing layer, an improved AΔR due to confinement of current flow through a smaller area, and increased MR due to the domain wall created within the magnetic nano-contact.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a magnetic head having a confined current path, and more specifically, to a ballistic magneto resistive (BMR) sensor having a free layer stabilized by an in-stack bias and spacer-decoupling layer including nanoparticles. 
     2. Related Art 
     In the related art magnetic recording technology such as hard disk drives, a head is equipped with a reader and a writer that operate independently of one another.  FIGS. 1  ( a ) and ( b ) illustrate related art magnetic recording schemes. A recording medium  1  having a plurality of bits  3  and a track width  5  has a magnetization  7  parallel to the plane of the recording media. As a result, a magnetic flux is generated at the boundaries between the bits  3 . This is commonly referred to as “longitudinal magnetic recording”. 
     Information is written to the recording medium  1  by an inductive write element  9 , and data is read from the recording medium  1  by a read element  11 . Coils  16  are used to supply a write current  17  to the inductive write element  9 , and a read current  15  is supplied to the read element  11 . An insulating layer (not illustrated for the sake of clarity) made of Al 2 O 3  or the like is deposited between the read element  11  and the write element  9  to avoid any interference between the respective read and write signals. 
     The read element  11  is a sensor that operates by sensing the resistance change as the sensor magnetization changes direction. A shield  13  reduces the undesirable magnetic fields coming from the media and prevents the undesired flux of adjacent bits from interfering with the one of the bits  3  that is currently being read by the read element  11 . 
     Due to requirements of increased bit and track density readable at a higher efficiency and speed, the related art magnetic recording scheme of  FIG. 1(   b ) has been developed. In this related art scheme, the direction of magnetization  19  of the recording medium  1  is perpendicular to the plane of the recording medium  1 . This is also known as “perpendicular magnetic recording”. This design provides more compact and stable recorded data. Also a soft underlayer (not illustrated) is required to increase the writer magnetic field efficiency. Further, an intermediate layer (not illustrated for the sake of clarity) can be used to control the exchange coupling between the recording layer  1  and soft underlayer. 
       FIGS. 2(   a )-( c ) illustrate various related art read heads for the above-described magnetic recording scheme, known as “spin valves”. In the bottom type spin valve illustrated in  FIG. 2(   a ), a free layer  21  operates as a read sensor to read the recorded data from the recording medium  1 . A spacer  23  is positioned between the free layer  21  and a composed pinned layer  25 . On the other side of the composed pinned layer  25 , there is an anti-ferromagnetic (AFM) layer  27 . In the top type spin valve illustrated in  FIG. 2(   b ), the position of the layers is reversed. 
       FIG. 2(   c ) illustrates a related art dual type spin valve. Layers  21  through  25  are substantially the same as described above with respect to  FIGS. 2(   a )-( b ). However, an additional spacer  29  is provided on the other side of the free layer  21 , upon which a second pinned layer  31  and a second AFM layer  33  are positioned. An extra signal provided by the second pinned layer  31  increases the resistance change ΔR. 
     The direction of magnetization in the pinned layer  25  is substantially fixed, whereas the direction of magnetization in the free layer  21  can be changed, for example (but not by of limitation) depending on the effect of an external magnetic field, such as the recording medium  1 . 
     When the external magnetic field is applied to a reader, the magnetization of the free layer  21  is altered, or rotated, by an angle. When the flux is positive the magnetization direction of the free layer  21  is rotated upward, and when the flux is negative the magnetization direction of the free layer  21  is rotated downward. If the applied external field changes the free layer  21  magnetization direction to be aligned in the same way as composed pinned layer  25 , then the resistance between the layers is low, and electrons can more easily migrate between those layers  21 ,  25 . 
     However, when the free layer  21  has a magnetization direction opposite to that of the composed pinned layer  25 , the resistance between the layers is high. This high resistance occurs because it is more difficult for electrons to migrate between the layers  21 ,  25 . Similar to the external field, the AFM layer  27  provides an exchange coupling and keeps the magnetization of composed pinned layer  25  substantially fixed. 
     The resistance change ΔR when the layers  21 ,  25  are parallel and anti-parallel should be high to have a highly sensitive reader. The media bit is decreasing in size, and the correspondingly, the magnetic field from the media bit is weaker. As a result, it is necessary for the free layer to sense this media flux having a reduced magnitude. Therefore, it is important for the related art free layer to have a reduced thickness to maintain sufficient sensitivity of the free layer. In order to provide a high-sensitivity sensor that can sense a very weak magnetic field, this is accomplished by reducing the free layer thickness to about 3 nm in the case of an areal recording density of 150 to 200 Gbits/in 2 . 
     However, as a result of the thin free layer, there is a related art problem of a stronger spin transfer effect. The spin transfer effect is substantially inversely proportional to the thickness of the film. Thus, the stability of the free layer is reduced. Further, there is also a need for a high resistance change ΔR between the layers  21 ,  25  of the related art read head. As discussed in greater detail below, a thicker free layer results in a higher value of ΔR. 
     The operation of the related art read head is now described in greater detail. In the recording media  1 , flux is generated based on polarity of adjacent bits in the case of longitudinal magnetic recording. If two adjoining bits have negative polarity at their boundary the flux will be negative. On the other hand, if both of the bits have positive polarity at the boundary the flux will be positive. The magnitude of flux determines the angle of magnetization between the free layer and the pinned layer. 
       FIG. 3  illustrates a related art synthetic spin valve. The free layer  21 , the spacer  23  and the AFM layer  27  are substantially the same as described above. However, the composed pinned layer  25  further includes a first pinned sublayer  35  separated from a second pinned sublayer  39  by a pinned layer spacer  37 . The first pinned sublayer  35  operates according to the above-described principle with respect to the composed pinned layer  25 . The second pinned sublayer  39  has an opposite spin state with respect to the first pinned sublayer  35 . As a result, the total composed pinned layer magnetic moment is reduced due to anti-ferromagnetic coupling between the first pinned sublayer  35  and the second pinned sublayer  39 . The synthetic read head has a composed pinned layer with a total magnetic flux close to zero, and thus greater stability and high pinning field can be achieved than with the single pinned layer structure. A buffer layer  28  is deposited below the AFM layer  27  for good spin-valve growth, and a cap  40  is provided on an upper surface of the free layer  21 . 
       FIG. 4  illustrates the related art shielded read head. As noted above, it is important to avoid the sensing of unintended magnetic flux from adjacent bits during the reading of a given bit. A cap (protective) layer  40  is provided on an upper surface of the free layer  21  to protect the spin valve against oxidation before deposition of top shield  43 , by electroplating in a separated system. Similarly, a bottom shield  45  is provided on a lower surface of the buffer layer  28 . 
     Related art magnetic recording schemes use a current perpendicular to plane (CPP) head, where the sensing current flows perpendicular to the spin valve plane. As a result, the size of the read head can be reduced without a loss of the output read signal. Various related art spin valves that operate in the CPP scheme are illustrated in  FIGS. 5(   a )-( c ), and are discussed in greater detail below. These spin-valves structurally differ primarily in the composition of their spacer  23 . The compositions and resulting difference in operation of these effects is discussed in greater detail below. 
       FIG. 5(   a ) illustrates a related art tunneling magnetoresistive (TMR) head for the CPP scheme. In the TMR head, the spacer  23  acts as an insulator, or tunnel barrier layer. Thus, in the case of a very thin barrier that is the spacer  23 , the electrons can migrate from free layer  21  to pinned layer  25  or verse versa without change of spin direction. Current related art TMR heads have an increased magnetoresistance (MR) on the order of about 30-50%. 
       FIG. 5(   b ) illustrates a related art CPP-GMR head. In this case, the spacer  23  acts as a conductor. In the related art CPP-GMR head, there is a need for a large resistance change ΔR, and a moderate element resistance for having a high frequency response. A low free layer coercivity is also required so that a small media field can be detected. The pinning field should also have a high strength. Additional details of the CPP-GMR head are discussed in greater detail below. 
       FIG. 5(   c ) illustrates the related art ballistic magnetoresistance (BMR) head. In the spacer  23 , which operates as an insulator, a ferromagnetic region  47  connects the pinned layer  25  to the free layer  21 . The area of contact is on the order of a few nanometers. This is referred to as a nano-path or a nano-contact. As a result, there is a substantially high MR, due to electrons scattering at the domain wall created within this nanocontact. Other factors include the spin polarization of the ferromagnets, and the structure of the domain that is in nano-contact with the BMR head. 
     In the foregoing related art heads, the spacer  23  of the spin valve is an insulator for TMR, a conductor for GMR, and an insulator having a magnetic nano-contact for BMR. While related art TMR spacers are generally made of insulating materials such as alumina, related art GMR spacers are generally made of conductive metals, such as copper. 
     In the related art GMR head, resistance is minimized when the magnetization directions (or spin states) of the free layer  21  and the pinned layer  25  are parallel and is maximized when the magnetization directions are opposite As noted above, the free layer  21  has a magnetization of which the direction can be changed. Thus, the GMR system avoids perturbation of the head output signal by minimizing the undesired switching of the pinned layer magnetization. 
     GMR depends on the degree of spin polarization of the pinned and free layers, and the angle between their respective magnetizations. Spin polarization depends on the difference between the spin state (up or down) in each of the free and pinned layers. As the free layer  21  receives the flux from the magnetic recording media, the free layer magnetization rotates by a small angle in one direction or the other, depending on the direction of flux. The change in resistance between the pinned layer  25  and the free layer  21  is proportional to angle between the moments of the free layer  21  and the pinned layer  25 , as noted above. There is a relationship between the resistance change ΔR and the output read signal. 
     The GMR head has various requirements. For example, but not by way of limitation, a large resistance change ΔR is required to generate a high output signal. In order to generate the large resistance change ΔR, it is desirable to have thicker free layer. This relationship is shown in  FIG. 6(   a ). A similar relationship exists between the MR ratio and free layer thickness, as shown in  FIG. 6(   b ). Therefore, the thinner free layer, which is required to sense a smaller media bit with a weaker signal, also has a lower MR and AΔR in the related art CPP scheme. As a result, the related art spin transfer effect problem is increased. 
     As noted above, further increasing capacity of disk drives requires a small, high-sensitivity MR head that corresponds to the miniaturization of the head size. As head size decreases, the head output signal decreases. Accordingly, the free layer must be more sensitive to the media magnetic field. As discussed in S. Z. Hua et al., Phys. Review B67, 060401 (R) (2003), a high resistance change ΔR can be obtained using the foregoing related BMR concept (i.e., connection of at least two ferromagnetic layers to one another via a nano-contact). A substantially high BMR value can be achieved (e.g., thousands of percent of MR ratio). 
     The basis of the above-described BMR is disclosed in G. Tatara et al., Phys. Review Letters, Vol. 83, 2030 (1999), based on the thin domain wall between the two adjacent ferromagnetic layers that are antiparallel to each other. 
     In the related art BMR head, a key factor is the magnetic domain structure. Its configuration control and stability during the read process are extremely important for high-out put signal t. Further, for proper use of the BMR head, it is necessary to stabilize the free layer against thermal agitation and spin transfer effect and make it mono-domain. 
     Stabilization of the free layer in the related art has been done in the case of CPP-GMR, via an in-stack bias. This configuration is disclosed in U.S. Patent Publication No. 2004/0008454. In this related art in-stack bias, a decoupling layer is formed as a spacer above the free layer. The decoupling layer is made of a continuous conductive film having a thickness of 1 nm to 2 nm. The film may be made of a metal such as Cr, Ta or Cu. 
     Additionally, Japanese Patent Application Publication No. 10-229013 discloses a magneto-resistive effect element with an in-stack bias. More specifically, a bias film having a structure such that it can stabilize the free layer in mono-domain magnetic structure. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to overcome the related art problems and disadvantages. However, such an object, or any object, need not be achieved in the present invention. 
     To achieve the above objects, a magnetic element including a spin valve is provided for reading a recording medium, and includes a free layer having a magnetization adjustable in response to an external field, a pinned layer having a substantially fixed magnetization, a spacer sandwiched between the pinned layer and the free layer, the spacer comprising a non-magnetic insulating matrix and a magnetic grain disposed therein to form nano-contacts, and an in-stack bias positioned on the free layer opposite the spacer, wherein the in-stack bias comprises a ferromagnetic layer pinned by exchange coupling with a first antiferromagnetic (AFM) layer, and an in-stack bias spacer including a magnetic grain disposed in an insulating matrix. The foregoing may also be implemented in a device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1(   a ) and ( b ) illustrates a related art magnetic recording scheme having in-plane and perpendicular-to-plane magnetization, respectively; 
         FIGS. 2(   a )-( c ) illustrate related art bottom, top and dual type spin valves; 
         FIG. 3  illustrates a related art synthetic spin valve for a magnetoresistive reader head; 
         FIG. 4  illustrates a related art synthetic spin valve having a shielded structure; 
         FIGS. 5(   a )-( c ) illustrates various related art magnetic reader spin valve systems; 
         FIGS. 6(   a )-( b ) illustrate the dependence of AΔR and MR, respectively on free layer thickness; 
         FIG. 7  illustrates magneto-resistive element according to a first exemplary, non-limiting embodiment of the present invention; 
         FIG. 8  illustrates magneto-resistive element according to a second exemplary, non-limiting embodiment of the present invention; 
         FIG. 9  illustrates magneto-resistive element according to a third exemplary, non-limiting embodiment of the present invention; 
         FIG. 10  illustrates magneto-resistive element according to a fourth exemplary, non-limiting embodiment of the present invention; and 
         FIG. 11  illustrates magneto-resistive element according to a fifth exemplary, non-limiting embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention includes an in-stack biased (also referred to as “exchange biased”) magnetic head having a confined current path according to the exemplary, non-limiting embodiments described herein, and equivalents thereof as would be known by one of ordinary skill in the art. 
     In the present invention, the term “read head” is used interchangeably with the term “magnetic sensor”, and refers to the overall apparatus for sensing data from a recording media. In this regard, “magnetic sensor” is one particular type of “magnetic element”, and where magnetic sensors are used in the specification, other magnetic elements (e.g., random access memory or the like) may be substituted therein, as would be known by one of ordinary skill in the art. 
     Additionally, the term “magnetic element” is defined to include “magnetoresistance effect element” and/or “magnetoresistance element” as is understand by those of ordinary skill in this technical field. However, the present invention is not limited thereto, and other definitions as would be understood by those of ordinary skill in the art may be substituted therefore without narrowing the scope of the invention. Further, the term “spin valve” is used to refer to the specific structural makeup of the read head layers. 
       FIG. 7  illustrates a BMR sensor (also referred to as a “magnetic sensor”) according to a first exemplary, non-limiting embodiment of the present invention. In this embodiment, a shield  101  is provided (preferably made of NiFe, but not limited thereto), upon which a buffer  103  is positioned. The buffer  103  is for good growth of an AFM layer  105  and the other films that are deposited on the buffer  103 . 
     The AFM layer  105  provides a coupling for a pinned layer  107  having a substantially fixed magnetization direction, which is positioned above the AFM layer  105 . The pinned layer  107  is preferably of a composed type, although another equivalent thereof, as would be known by one of ordinary skill in the art (e.g., single layer) may also be used. The composed pinned layer  107  includes a first pinned sublayer  109  spaced apart from a second pinned sublayer  113  by a non-magnetic pinned layer spacer  111 . For example, but not by way of limitation, these first and second pinned sublayers  109 ,  111  may be ferromagnetic. 
     A spacer  115  is positioned between the pinned layer  107  and a free layer  117 . The spacer  115  is a film having nano-contacts  116  disposed in a non-magnetic insulating matrix (e.g., a nano-contact is made of a magnetic grains in an insulating matrix). At least one of the grains reaches both surfaces of the free layer and the pinned layer. The nano-contact is one or more grains. Preferably, only a substantially few grains for each nano-contact is preferred. 
     The free layer  117  is provided above the spacer  115 . As is the case in the related art, the magnetization direction of the free layer can rotate or switch in response to an external magnetic field. The magnetization direction is adjustable by the magnetic field. For example, but not by way of limitation, the external field may be generated from a medium such as a hard disk, and the pinned layer has a substantially fixed magnetization direction. 
     An in-stack bias  119  is positioned above the free layer  117  opposite to the spacer  115 . The in-stack bias  119  includes an in-stack bias spacer  120  positioned between the free layer  117  and a ferromagnetic layer  123 . The in-stack bias spacer  120  includes a second nano-contact  121  disposed in a non-magnetic insulating matrix  122 . 
     Another AFM layer  125  is provided above the ferromagnetic layer  123  to substantially (i.e., except for external magnetization effects, such as “noise” from the device in which the present invention is applied) fix its magnetization direction and to form the upper portion of the in-stack bias  119 . The magnetization direction of the ferromagnetic layer  123  is pinned by exchange coupling with the AFM layer  125 . Atop shield  127  is provided above the in-stack bias  119 , and an insulator  129  is provided between the top and bottom shields  101 ,  127 , respectively, and on outside of the BMR sensor ( 103  through  125 ). A capping layer  126  is deposited on the top of the AFM layer  125  to protect the spin-valve stack against oxidation before top shield deposition. 
     In the foregoing exemplary, non-limiting embodiment of the present invention, the film structure of the in-stack bias  119  includes the in-stack bias spacer  120  which minimizes the exchange coupling between the free layer  117  and the ferromagnetic layer  123 , thus stabilizing the free layer  117  in the mondomain structure by magnetostatic coupling with the ferromagnetic layer  123 . Additionally, the current flows through the smaller space of the second nano-contacts  121 , such that the effective area A is reduced, the ΔR is increased. Further, the MR ratio increases, resulting in additional ballistic magnetoresistive effect due to the creation of a domain wall within the magnetic nano-contact of the in-stack bias spacer  120 . 
     As noted above, the pinned layer  107  can be a single ferromagnetic pinned layer or composed pinned layer. The composed pinned layer comprises the first pinned sublayer  109  and the second pinned sublayer  113 . The magnetizations of these sublayers  109  and  113  are coupled antiferromagnetically to each other. The first and second pinned sublayers  109 ,  113  comprise a ferromagnetic material. A pinned layer spacer  111  is positioned between the layer  109  and the layer  113 . The ferromagnetic material in the pinned layer  107  comprises one of Fe, Ni and Co. The pinned layer  107  has a total thickness between about 3 nm and 8 nm. The non-magnetic pinned layer spacer  111  is made of at least one of Ru, Rh, Pd, Pt, Ir, Os, Ag and Cu, or alloys thereof, and has a thickness between about 0.3 nm and 1 nm. 
     In the foregoing embodiment, the pinned layer  107  magnetization is disclosed to be pinned by the AFM layer  105 . However, the present invention is not limited thereto, and alternative structures may be used, as would be understood by one of ordinary skill in the art. For example, but not by way of limitation, instead of being substantially fixed by the AFM layer  105 , the pinned layer  107  may be self-pinned by a hard magnetic layer. 
     In the present invention, the sensing current flows in the film thickness direction (e.g., from the bottom shield to the top shield or the opposite direction). This is called Current-perpendicular-to-plane (CPP) geometry. 
       FIG. 8  illustrates a second, non-limiting embodiment of the present invention. In this embodiment, those features that are the same as the first embodiment of  FIG. 7  are not repeated. In  FIG. 8 , the free layer  117  is a composed free layer, and includes a free layer spacer  203  positioned between an upper sublayer (first free sublayer)  201  and a lower sublayer (second free sublayer)  205  of the free layer  117 . The free layer spacer  203  is made of at least one of Ru, Rh, Pd, Pt, Ir, Os, Ag and Cu, or alloys thereof, and has a thickness between about 0.3 nm and 1 nm. The two sublayers  201 ,  205  of the free layer  117  have a total thickness between about 1 nm and 5 nm. 
       FIG. 9  illustrates a third, exemplary, non-limiting embodiment of the present invention. In this embodiment, those features that are the same as the first embodiment of  FIG. 7  are not repeated. In  FIG. 9 , the free layer  117  is a composed free layer, and includes at least two, and preferably three, ferromagnetic sublayers  301 ,  303 ,  305  deposited on each other. 
       FIG. 10  illustrates a fourth, exemplary, non-limiting embodiment of the present invention. In this embodiment, those features that are the same as the first embodiment of  FIG. 7  are not repeated. In  FIG. 10 , the ferromagnetic layer  401 , the first AFM layer  403  and the capping layer  404  are deposited after patterning of the MR element and deposition of the insulator  129 . As a result, those layers  401 ,  403  of the in-stack bias  119  are larger than the free layer  117 . Thus, the in-stack bias  119  further stabilizes the free layer  117  at its edges (i.e., at the edge of the sensor). Because the in-stack bias  119  is larger than the free layer  117 , and does not stop at the substantially same point as in the previous embodiments (i.e., the edges of the in-stack bias  119  extend beyond the edges of the free layer  117 ), this further stabilization can be achieved. 
     As the BMR sensor decreases in size and the chance of damage increases during lithography and ion milling if those steps are used, this embodiment avoids this edge effect. Further, as the vortex effect becomes dominant for a smaller size element, this exemplary embodiment substantially reduces the production of noise. 
       FIG. 11  illustrates a fifth, non-limiting exemplary embodiment of the present invention. In this embodiment, those features that are the same as the first embodiment of  FIG. 7  are not repeated. In  FIG. 11 , an additional hard bias stabilizer  501  is provided on top of insulator  129 . As a result, the free layer is further stabilized in an efficient manner. The hard bias stabilizer  501  is chosen from hard materials group including CoCr, CoPt and CoCrPt with a thickness from about 5 nm to 30 nm. This additional hard bias stabilizer  501  may also be used with the third and fourth embodiments as discussed above and illustrated in the drawings. The capping layer  126  is positioned above the first AFM  125 . 
     For all of the above exemplary, non-limiting embodiments of the present invention, the ferromagnetic material in the free layer is of at least one of Ni, Fe, and Co. Alloys of CoNi, CoFe, NiFe, CoFeNi or any combination thereof is preferred. Further, either or both of the AFM layers  105 ,  125  is made of at least one of PtMn and IrMn, and has a thickness between about 5 nm and 20 nm. More generally, either or both of these AFM layers  105 ,  125  can be made of X—Mn or XY—Mn, where X and Y are made of Pt, Ir, Pd, Ru, Rh, Os, Fe and Ni, and X is different from Y The capping layer  126  is made of at least one of Ta, Cr, Ru, Au and other non-magnetic materials and has a thickness of about 2 to 5 nm. 
     The first nano-contacts  116  and second nano-contacts  121  comprise at least one of Ni, Co and Fe, and have a diameter of less than about 10 nm. Further, the surrounding insulating matrix (insulator) in the spacer  120  includes at least one of oxides or nitrides such as Al 2 O 3 , AlN, SiO 2  and Si 3 N 4 . This material can also be a highly resistive, insulator having a resistivity higher than about 100 μΩ×cm. Alternatively, the nano-contact  116  may be surrounded by a non-magnetic, conductive matrix made of conductive material such as Cu, Au, Cr or equivalent thereof as the matrix. 
     With respect to the second nano-contact  121  in the in-stack bias layer  120 , the surrounding insulator)  122  includes oxides and/or nitrides, or a high resistivity material of about 100 μΩ×cm or higher. The second nano-contact  121  can also be surrounded by a non-magnetic conductive material. 
     Further, in  FIGS. 8-11 , the direction of magnetization of the in-stack bias  123  (not illustrated for the sake of clarity) is opposite to the direction of the free layer  117 . However, the present invention is not limited thereto, and other configurations as may be envisioned by one of ordinary skill in the art may also be used. 
     The present invention has various advantages. For example, but not by way of limitation, the present invention includes a BMR sensor having a free layer stabilized by in-stack bias and an in-stack bias spacer having a nano-contact. As a result, the stability of the free layer is maintained and the effective area of the MR element is reduced due to the confined current path, which results in a higher output read signal. 
     Additionally, a domain wall is created between the free layer and the ferromagnetic pinned layer used in the stabilizer. Thus, there is an improvement in the MR ratio and resistance change. 
     Further, in the present invention, a method is provided for preparing the free layer having grains disposed in a matrix made by ion beam sputtering method using a target having at least magnetic material and insulator (e.g. magnetic material like Ni and insulator like Al 2 O 3 . Ni grows as grains surrounded by Al 2 O 3 ). The surface is etched to ensure that those grains reach the surface to form the nano-contact. 
     Additionally, the foregoing embodiments are generally directed to a magnetoresistive element for a magnetoresistive read head. This magnetoresistive read head can optionally be used in any of a number of devices. For example, but not by way of limitation, as discussed above, the read head can be included in a hard disk drive (HDD) magnetic recording device. However, the present invention is not limited thereto, and other devices that uses the ballistic magnetoresistive effect may also comprise the magnetoresistive element of the present invention. For example, but not by way of limitation, a magnetic random access memory (i.e., a magnetic memory device provided with a nano-contact structure, or a device) may also employ the present invention. Such applications of the present invention are within the scope of the present invention. 
     The present invention is not limited to the specific above-described embodiments. It is contemplated that numerous modifications may be made to the present invention without departing from the spirit and scope of the invention as defined in the following claims.