Abstract:
An SV sensor with the preferred structure Substrate/Seed/Free/Spacer/Pinned/AFM/Cap where the seed and cap layers are formed of a non-magnetic, electrically insulating oxide, NiMnO x . The non-magnetic electrically insulating NiMnO x  seed layer results in enhanced GMR coefficient and improved thermal stability of the SV sensor. The improved thermal stability enables use of Ni—Mn with its high blocking temperature and strong pinning field as the AFM layer material, as well as other Mn alloys, without SV sensor performance degradation from the high temperature anneal step needed to develop the desired exchange coupling. The electrically insulating property of the NiMnO x  seed and cap layer material decreases sense current shunting and further reduces shield/sensor shorting.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to spin valve magnetic transducers for reading information signals from a magnetic medium and, in particular, to a spin valve sensor with enhanced GMR effect and improved thermal stability, and to magnetic storage systems which incorporate such sensors. 
     2. Description of Related Art 
     Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces. 
     In high capacity disk drives, magnetoresistive (MR) read sensors, commonly referred to as MR heads, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater track and linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer. 
     The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization in the MR element and the direction of sense current flow through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance of the MR element and a corresponding change in the sensed current or voltage. 
     Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers. 
     GMR sensors using only two layers of ferromagnetic material (e.g., Ni—Fe) separated by a layer of non-magnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors manifesting the SV (GMR) effect. In an SV sensor, one of the ferromagnetic layers, referred to as the pinned layer, has its magnetization typically pinned by exchange coupling with an antiferromagnetic (e.g., NiO or Fe—Mn) layer. The pinning field generated by the antiferromagnetic layer should be greater than demagnetizing fields (about 200 Oe) at the operating temperature of the SV sensor (about 120 C) to ensure that the magnetization direction of the pinned layer remains fixed during the application of external fields (e.g., fields from bits recorded on the disk). The magnetization of the other ferromagnetic layer, referred to as the free layer, however, is not fixed and is free to rotate in response to the field from the recorded magnetic medium (the signal field). In SV sensors, the SV effect varies as the cosine of the angle between the magnetization of the pinned layer and the magnetization of the free layer. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in direction of magnetization in the free layer, which in turn causes a change in resistance of the SV sensor and a corresponding change in the sensed current or voltage. IBM&#39;s U.S. Pat. No. 5,206,590 granted to Dieny et al., incorporated herein by reference, discloses a GMR sensor operating on the basis of the SV effect. 
     FIG. 1 shows a prior art SV sensor  100  comprising end regions  104  and  106  separated by a central region  102 . A free layer (free ferromagnetic layer)  110  is separated from a pinned layer (pinned ferromagnetic layer)  120  by a non-magnetic, electrically-conducting spacer layer  115 . The magnetization of the pinned layer  120  is fixed by an antiferromagnetic (AFM) layer  125 . Free layer  110 , spacer layer  115 , pinned layer  120  and the AFM layer  125  are all formed in the central region  102 . Hard bias layers  130  and  135  formed in the end regions  104  and  106 , respectively, provide longitudinal bias for the free layer  110 . Leads  140  and  145  formed over hard bias layers  130  and  135 , respectively, provide electrical connections for the flow of the sensing current I S  from a current source  160  to the MR sensor  100 . Sensing means  170 , typically includes a recording channel such as a partial-response maximum-likelihood (PRML) channel, connected to leads  140  and  145  sense the change in the resistance due to changes induced in the free layer  110  by the external magnetic field (e.g., field generated by a data bit stored on a disk). 
     As mentioned above, the magnetization of the pinned layer  120  in the prior art SV sensor  100  is generally fixed through exchange coupling with AFM layer  125  of antiferromagnetic material such as Fe—Mn or NiO. However, both Fe—Mn and NiO have rather low blocking temperatures (blocking temperature is the temperature at which the pinning field for a given material reaches zero Oe) which make their use as an AFM layer in an SV sensor difficult and undesirable. 
     A desirable alternate AFM material is Ni—Mn which has much higher corrosion resistance than Fe—Mn, very large exchange pinning at room temperature, and much higher blocking temperature than either Fe—Mn or NiO. High blocking temperature is essential for SV sensor reliability since SV sensor operating temperatures can exceed 120 C in some applications. 
     Referring to FIG. 2, there is shown the change in the unidirectional anisotropy field (H UA ) or pinning field versus temperature for 50 Å thick Ni—Fe pinned layers using Fe—Mn, NiO and Ni—Mn as the pinning layers. Fe—Mn has a blocking temperature of about 180 C (curve  210 ) and NiO has a blocking temperature of about 220 C (curve  220 ). Considering that a typical SV sensor used in a magnetic recording disk drive should be able to operate reliably at a constant temperature of about 120 C with a pinning field of at least 200 Oe, it can readily be seen that Fe—Mn substantially loses it ability to pin the pinned layer at about 120 C (pinning field dropping to about 150 Oe) and NiO can only marginally provide adequate pinning at about 120 C (pinning field dropping to about 170 Oe). It should be noted that once the pinning effect is lost, the SV sensor loses its SV effect either totally or partially, rendering the SV sensor useless. In contrast, it can be seen in FIG. 2 that Ni—Mn with a blocking temperature of beyond 450 C (curve  230 ) easily meets the pinning field requirements at the 120 C operating temperature of typical SV sensors. 
     However, the problem with using Ni—Mn AFM for the pinning layer is the requirement for a high temperature (equal or greater than 240 C) annealing step after the deposition of the SV sensor layers (post-annealing) to achieve the desired exchange coupling between the Ni—Mn pinning layer and the Ni—Fe pinned layer in order to achieve proper SV sensor operation. Unfortunately, annealing at such high temperature (equal or greater than 240 C) substantially degrades the GMR coefficient of the SV sensor. This irreversible degradation of the SV sensor is believed to be caused by interdiffusion at layer interfaces. Stability against this interdiffusion is a prerequisite for the use of Ni—Mn as the AFM layer in an SV sensor because the SV sensor must survive the severe heat treatment required to anneal the Ni—Mn. In addition, the magnetostriction of the free layer increases sharply after annealing. This increase in the magnetostriction is believed to be caused by intermixing at the interface between the seed layer and the free layer. 
     Therefore there is a need for an SV sensor using a Ni—Mn AFM pinning layer that can withstand the annealing step required to achieve the desired exchange coupling without the undesirable degradation of the SV effect and without problems in control of magnetostriction of the free layer. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to disclose an improved seed layer for SV sensors with the film structure Seed/Free/Spacer/Pinned/AFM/Cap wherein the improved seed layer results in enhanced GMR effect and improved thermal stability. 
     It is another object of the present invention to disclose an SV sensor having an improved seed layer which allows the use of a Ni—Mn layer as the pinning layer. 
     It is a further object of the present invention to disclose an improved SV sensor having the film structure NiMnO x /Ni—Fe/Co/Cu/Co/Ni—Mn/Ta wherein the annealing step to develop exchange coupling is carried out without serious degradation of the GMR effect. 
     It is a further object of the present invention to disclose an improved SV sensor having the film structure NiMnO x /Ni—Fe/Co/Cu/Co/Ni—Mn/NiMnO y  wherein the annealing step to develop exchange coupling is carried out without serious degradation of the GMR effect. 
     It is yet another object of the present invention to disclose an SV sensor having a nonmagnetic seed layer and a cap layer wherein said seed layer and cap layer form part of the top and bottom read gaps, respectively, resulting in reduced shield to sensor shorting. 
     In accordance with the principles of the present invention, there is disclosed an SV sensor with the preferred structure of Substrate/NiMnO x /Ni—Fe/Co/Cu/Co/Ni—Mn/NiMnO y . The NiMnO x  seed layer on the substrate affects the properties of subsequent layers deposited over said seed layer resulting in improved GMR effect and improved thermal stability of the SV sensor. 
     In accordance with the principles of an alternative embodiment of the present invention, there is disclosed an SV sensor with the preferred structure of Substrate/NiMnO x /Ni—Fe/Co/Cu/Co/Ni—Mn/Ta. The NiMnO x  seed layer on the substrate affects the properties of subsequent layers deposited over said seed layer resulting in improved GMR effect and improved thermal stability of the SV sensor. 
     In accordance with the principles of an alternative embodiment of the present invention, there is disclosed an anti-parallel (AP)-pinned SV sensor with the preferred structure of Substrate/NiMnO x /Ni—Fe/Co/Cu/AP 1 /APC/AP 2 /Ni—Mn/Ta where AP 1  is the first AP-pinned layer, AP 2  is the second AP-pinned layer and APC is an anti-parallel coupling layer. The NiMnO x  seed layer on the substrate affects the properties of subsequent layers deposited over said seed layer resulting in improved GMR effect and improved thermal stability of the AP-pinned SV sensor. 
     The NiMnO x  and NiMnO y  materials used in forming the seed layer and the cap layer, respectively, of the SV sensor of the preferred embodiment of the present invention is non-magnetic and electrically insulating. The non-magnetic, electrically insulating seed layer and cap layer form part of the bottom read gap and the top read gap, respectively, which separate the SV sensor from the bottom and top magnetic shields respectively. The use of electrically insulating material for the seed layer and the cap layer reduces SV sensor to shield shorting and does not add to sense current shunting as does the use of metal seed layers and cap layers. 
     The above as well as additional objects, features, and advantages of the present invention will become apparent in the following detailed written description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a fuller understanding of the nature and advantages of the present invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings. 
     FIG.,  1  is an air bearing surface view of a prior art SV sensor; 
     FIG. 2 is a graph showing temperature dependence of the pinning fields for exchange coupling of Fe—Mn, NiO and Ni—Mn antiferromagnetic pinning layers to Ni—Fe ferromagnetic pinned layers; 
     FIG. 3 is a simplified drawing of a magnetic recording disk drive system of the present invention; 
     FIG. 4 is an air bearing surface view, not to scale, of the SV sensor of the present invention; 
     FIGS.  5   a  and  5   b  are graphs showing the high field magnetoresistance hysteresis curves of SV sensors fabricated with Ta seed and cap layers and the present invention NiMnO x  seed layer and NiMnO y  cap layer, respectively; 
     FIGS.  6   a  and  6   b  are graphs showing the effect of annealing time at 280 C on the unidirectional anisotropy fields and the GMR coefficients, respectively, for the Ni—Mn SV sensors with Ta and NiMnO x  seed layers; 
     FIG. 7 is a sectional view perpendicular to the air bearing surface of the read head of the present invention including the SV sensor and the shield layers; 
     FIG. 8 is an air bearing surface view, not to scale, of an alternative embodiment of the SV sensor of the present invention; and 
     FIG. 9 is an air bearing surface view, not to scale, of another alternative embodiment of the SV sensor of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The following description is the best embodiment presently contemplated for carrying out the present invention. This description is made for the purpose of illustrating the general principles of the present invention and is not meant to limit the inventive concepts claimed herein. 
     Referring now to FIG. 3, there is shown a disk drive  300  embodying the present invention. As shown in FIG. 3, at least one rotatable magnetic disk  312  is supported on a spindle  314  and rotated by a disk drive motor  318 . The magnetic recording media on each disk is in the form of an annular pattern of concentric data tracks (not shown) on disk  312 . 
     At least one slider  313  is positioned on the disk  312 , each slider  313  supporting one or more magnetic read/write heads  321  where the head  321  incorporates the MR sensor of the present invention. As the disks rotate, slider  313  is moved radially in and out over disk surface  322  so that heads  321  may access different portions of the disk where desired data is recorded. Each slider  313  is attached to an actuator arm  319  by means of a suspension  315 . The suspension  315  provides a slight spring force which biases slider  313  against the disk surface  322 . Each actuator arm  319  is attached to an actuator means  327 . The actuator means as shown in FIG. 3 may be a voice coil motor (VCM). The VCM comprises a coil movable within a fixed magnetic field, the direction and speed of the coil movements being controlled by the motor current signals supplied by controller  329 . 
     During operation of the disk storage system, the rotation of disk  312  generates an air bearing between slider  313  (the surface of slider  313  which includes head  321  and faces the surface of disk  312  is referred to as an air bearing surface (ABS)) and disk surface  322  which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension  315  and supports slider  313  off and slightly above the disk surface by a small, substantially constant spacing during normal operation. 
     The various components of the disk storage system are controlled in operation by control signals generated by control unit  329 , such as access control signals and internal clock signals. Typically, control unit  329  comprises logic control circuits, storage means and a microprocessor. The control unit  329  generates control signals to control various system operations such as drive motor control signals on line  323  and head position and seek control signals on line  328 . The control signals on line  328  provide the desired current profiles to optimally move and position slider  313  to the desired data track on disk  312 . Read and write signals are communicated to and from read/write heads  321  by means of recording channel  325 . 
     The above description of a typical magnetic disk storage system, and the accompanying illustration of FIG. 3 are for representation purposes only. It should be apparent that disk storage systems may contain a large number of disks and actuators, and each actuator may support a number of sliders. 
     FIG. 4 shows an air bearing surface (ABS) view of the SV sensor  400  according to the preferred embodiment of the present invention. SV sensor  400  comprises end regions  404  and  406  separated from each other by a central region  402 . The substrate  450  can be any suitable substance, including glass, semiconductor material, or a ceramic material, such as alumina (Al 2 O 3 ). The seed layer  440  is a layer deposited to modify the crystallographic structures of the subsequent layers. In previous SV sensors, the seed layer material commonly used is tantalum (Ta). In the present invention, an improved seed layer  440  is formed of NiMnO x  where oxidation is sufficient to make the NiMnO x  nonmagnetic and electrically insulating. A free layer (free ferromagnetic layer)  410 , deposited on the seed layer  440 , is separated from a pinned layer (pinned ferromagnetic layer)  420  by a non-magnetic spacer layer  415 . In the preferred embodiment of the present invention, spacer layer  415 , formed over the free layer  410 , is also an electrically conducting layer. The magnetization of the free layer  410  is preferably parallel to the ABS in the absence of an external field. The magnetization of the pinned layer  420  is fixed by an antiferromagnetic (AFM) layer  430  and is preferably perpendicular to the ABS. A cap layer  405 , deposited on the AFM layer  430 , completes the central region  402  of the SV sensor  400 . In the present invention, the cap layer  405  is formed of nonmagnetic, electrically insulating NiMnO x . 
     Referring to FIG. 4, the SV sensor  400  further comprises layers  434  and  436  formed on the end regions  404  and  406 , respectively, for providing a longitudinal bias field to the free layer  410  to ensure a single magnetic domain state in the free layer. Lead layers  460  and  465  are also deposited on the end regions  404  and  406 , respectively, to provide electrical connections for the flow of the sensing current I S  from a current source  470  to the SV sensor  400 . Sensing means  480  which is electrically connected to leads  460  and  465  sense the change in the free layer resistance due to changes induced in the free layer  410  by the external magnetic field (e.g., field generated by a data bit stored on a disk). The external magnetic field acts to rotate the direction of magnetization of the free layer  410  relative to the direction of magnetization of the pinned layer  420  which is preferably pinned perpendicular to the ABS. Sensing means  480  preferably includes a digital recording channel such as a PRML channel as is known to those skilled in the art. Sensing means  480  also includes other supporting circuitries such as a preamplifier (electrically positioned between the sensor and the channel) for conditioning the sensed resistance changes as is known to those skilled in the art. 
     The SV sensor of the present invention is fabricated using ion beam sputtering methods to sequentially deposit the layers of SV sensor  400  shown in FIG.  4 . The sputter deposition process for fabrication of SV sensor  400  is started with deposition on a substrate  450  formed of alumina (Al 2 O 3 ) of a seed layer  440  formed of NiMnO x . The NiMnO x  is deposited by reactive sputtering from an Ni—Mn target in an argon/oxygen gas mixture where oxidation is sufficient to result in a nonmagnetic, electrically insulating NiMnO x  layer having a thickness of about 50 Å. Free layer  410  is preferably formed as a laminated structure comprising a Ni—Fe layer 35 Å thick deposited on and in contact with seed layer  440  and a cobalt (Co) layer 10 Å thick deposited on and in contact with the Ni—Fe layer. Alternatively, free layer  410  may be formed of a permalloy (Ni—Fe) film 50 Å thick deposited on and in contact with seed layer  440 . Spacer layer  415  formed of a copper (Cu) film 26 Å thick is deposited on and in contact with the free layer  410  and pinned layer  420  formed of a cobalt (Co) film 30 Å thick is deposited on and in contact with the spacer layer  415 . AFM layer  430  formed of a Ni—Mn film 250 Å thick is deposited on and in contact with the pinned layer  420 . The preferred composition of the Ni—Mn AFM layer is a Mn content in the range between 46 and 60 atomic percent. Cap layer  405  formed of a NiMnO y  film 50 Å thick completes the structure of the central portion  402  of the SV sensor  400 . 
     The preferred composition of the non-magnetic, electrically insulating NiMnO material used to form the seed layer of the present invention may be expressed as follows: 
     
       
         (Ni a —Mn b ) z —O x   
       
     
     
       
           a+b =100%, 10%&lt; a &lt;90%, 10%&lt; b &lt;90%, and 
       
     
     
       
           x+z =100%, 45%&lt; z &lt;95%, 5%&lt; x &lt;55%. 
       
     
     The preferred composition of the non-magnetic, electrically insulating NiMnO material used to form the cap layer of the present invention may be expressed as follows: 
     
       
         (Ni a —Mn b ) z —O y   
       
     
     
       
           a+b =100%, 10%&lt; a &lt;90%, 10%&lt; b &lt;90%, and 
       
     
     
       
           y+z =100%, 45%&lt; z &lt;95%, 5%&lt; y &lt;55%. 
       
     
     In the preferred embodiment of the present invention, NiMnO composition is (Ni 50 Mn 50 ) 90 O 10 . The as-deposited Ni—Mn AFM layer  430  does not show significant exchange coupling to the underlying pinned layer  420 . To develop the desired exchange coupling, SV sensor  400  is thermally annealed at a temperature of 280 C for about 2 hours. In previous Ni—Mn AFM SV sensors, this high temperature annealing process degraded the GMR coefficient due to interdiffusion at layer interfaces of the SV sensor. In the present invention, the use of NiMnO x  as the seed layer for SV sensor  400  results in improved thermal stability of the SV sensor so that after the annealing process at 280 C for about 2 hours to set the Ni—Mn AFM layer exchange coupling with the pinned layer, the SV sensor exhibits a high GMR coefficient, delta R/R, with high unidirectional anisotropy field (H UA ) 
     Referring now to FIGS.  5   a  and  5   b , the magnetoresistance of SV sensors fabricated with Ta seed and cap layers and with the NiMnO x  seed and cap layers of the present invention, respectively, are shown (the composition of all other layers in the SV sensors were kept the same). FIG.  5   a  is a graph of the high field magnetoresistance hysteresis curves obtained at room temperature (RT)  510  and at 120 C  520  for a Ta/Ni—Fe/Co/Cu/Co/Ni—Mn/Ta SV sensor after annealing for 2 hours at 280 C. FIG.  5   b  is a graph of the high field magnetoresistance hysteresis curves obtained at RT  530  and at 120 C  540  for a NiMnO x /Ni—Fe/Co/Cu/Co/Ni—Mn/NiMnO y  SV sensor after annealing for 2 hours at 280 C. At RT, the GMR coefficient, delta R/R, of 6.3% for the SV sensor fabricated with the NiMnO x  seed and cap layers is an improvement of 80% over the comparable SV sensor fabricated by the same process but with Ta seed and cap layers. At 120 C (typical SV sensor operating temperature), the delta R/R of 4.4% is an improvement of 69% over the SV sensor with Ta seed and cap layers. The unidirectional anisotropy field, H UA , of 630 Oe and the coercivity, H CE , of 291 Oe at 120 C remain nearly as high as the values at room temperature. These values are higher than those for the SV sensor with Ta seed and cap layers. 
     Further annealing of the Ni—Mn AFM SV sensors with Ta and NiMnO x  seed layers for up to 20 hours at 260 C does not cause any noticeable changes in H UA , H CE  and delta R/R. This indicates that, in the magnetic head (merged read sensor and write head) fabrication process where hardbakes of photoresists and annealing of write head poles at temperatures up to 260 C are performed, no noticeable changes in H UA , H CE  and delta R/R properties occur. To find the upper limit of thermal stability, these Ni—Mn AFM SV sensors were further annealed at 280 C, a high temperature typically not used for the head fabrication process. 
     FIGS.  6   a  and  6   b  show H UA  and delta R/R, respectively, versus annealing time at 280 C for NiMnO x /Ni—Fe/Co/Cu/Co/Ni—Mn/NiMnO x  and Ta/Ni—Fe/Co/Cu/Co/Ni—Mn/Ta SV sensors. As shown in FIG.  6   a , H UA  continues to increase with annealing time, reaching a value of approximately 640 Oe in 2 hours for the SV sensor with NiMnO x  seed layer  610  while taking 8 hours to reach the same value for the SV sensor with Ta seed layer  620 . Therefore, it is apparent that the use of the NiMnO x  seed layer leads to faster development of exchange coupling. On the other hand, as shown in FIG.  6   b  the GMR coefficients of both Ni—Mn SV sensors  630 ,  640  decrease with annealing time. However, the GMR coefficient of the Ni—Mn SV sensor with the NiMnO x  seed layer  630  after annealing for 20 hours is still higher than that of the Ni—Mn SV sensor with the Ta seed layer  640  after annealing for only 2 hours. This demonstrates the excellent thermal stability of the Ni—Mn SV sensor of the present invention. 
     This improvement in thermal stability may originate from unbonded “active” oxygen elements at the NiMnO x /Ni—Fe interface which are redistributed in interstitial sites after annealing, thereby preventing interdiffusion of metallic elements. In addition, the elimination of intermixing of Ta, Ni and Fe elements leads to easier control of magnetostriction of the free layer. 
     FIG. 7 is a sectional view perpendicular to the ABS of the SV sensor of the present invention showing a section through the central region  402  and including the shield and gap structure of the read head. The read head  700  comprises SV sensor  730  disposed between and in contact with bottom read gap  722  and top read gap  744  which in turn lie between bottom shield  710 , S 1 , and top shield  750 , S 2 . In merged read/write head structures, top shield S 2  also serves as the bottom pole P 1  of the write head which is formed on top of the read head structure  700 . Shields S 1  and S 2 , which serve to shield the SV sensor from unwanted magnetic fields, are formed of low coercivity ferromagnetic material such as permalloy which are also electrically conductive. Bottom gap  722  and top gap  744  must be formed of electrically insulating material to prevent electrical shorting of the SV sensor  730  to the bottom and top shields  710 ,  750 , respectively. The commonly used gap material is aluminum oxide (Al 2 O 3 ). For the SV sensor  730  of the present invention, seed layer  724  is formed of electrically insulating NiMnO x  formed on the bottom gap  722 , and therefore forms a laminated bilayer bottom gap  720 . Similarly, cap layer  742  is formed of electrically insulating NiMnO y  on which the top gap  744  is deposited, therefore forming a laminated bilayer top gap  740 . The additional electrical insulation provided by seed layer  724  and cap layer  742  to the bottom gap  722  and the top gap  744 , respectively, minimizes shield/SV sensor shorting in this read head structure. The use of electrically insulating NiMnO x  for the seed and cap layers of SV sensors, replacing the prior art tantalum layers, also reduces sense current shunting providing a further improvement in the SV sensors of the present invention. 
     FIG. 8 shows an ABS view of the SV sensor  800  according to an alternate embodiment of the present invention. Seed layer  840  is a layer of NiMnO x  having a thickness of about 50 Å deposited on substrate  450 . Free layer  410  is formed as a laminated structure comprising a permalloy (Ni—Fe) layer having a thickness of 35 Å deposited on and in contact with seed layer  840  and a Co layer having a thickness of 10 Å deposited on and in contact with the Ni—Fe layer. Alternatively, free layer  410  may be formed of a single Ni—Fe layer having a thickness of 50 Å deposited on and in contact with seed layer  840 . Spacer layer  415  formed of a Cu film having a thickness of 26 Å is deposited on and in contact with the free layer  410 . Pinned layer  420  formed of a Co film having a thickness of 30 Å is deposited on and in contact with the spacer layer  415 . AFM layer  430  formed of a Ni—Mn film having a thickness of 250 Å is deposited on and in contact with pinned layer  420 . Cap layer  805  formed of tantalum (Ta) is deposited on the AFM layer  430 . To develop the desired exchange coupling of the Ni—Mn AFM layer  430  to the underlying pinned layer  420 , SV sensor  800  is thermally annealed at a temperature of 280 C for a period of 2 hours. After this annealing process to set the Ni—Mn layer exchange coupling with the pinned layer, SV sensor  800  exhibits high GMR coefficient and high unidirectional anisotropy field, H UA . 
     FIG. 9 shows an ABS view of an antiparallel(AP)-pinned SV sensor  900  according to an another alternative embodiment of the present invention. All the layers of AP-pinned SV sensor  900  are same as those of SV sensor  400  except for pinned layer  420  and cap layer  405  which are replaced by laminated AP-pinned layer  920  and cap layer  905 , respectively. Laminated AP-pinned layer  920  comprises a first ferromagnetic pinned layer  922  and a second ferromagnetic pinned layer  924  separated from each other by an antiparallel coupling (APC) layer  926  of nonmagnetic material that allows said first and second ferromagnetic pinned layers  922 ,  924  to be coupled together antiferromagnetically. First pinned layer  922  may be made of Co, NiFe or Co/Ni—Fe. Second pinned layer  924  may be made of Co or Ni—Fe. APC layer  926  may be made of ruthenium (Ru), iridium (Ir) or Rhodium (Rh). Cap layer  905  is preferably formed of nonmagnetic, electrically insulating NiMnO x . Alternatively, cap layer  905  may be formed of tantalum (Ta). U.S. Pat. No. 5,465,185 granted to Heim et al., Nov. 7, 1995, and incorporated herein by reference, discloses an AP-pinned SV sensor and its principle of operation. 
     It will be apparent to those skilled in the art that alternative AFM layer  430  materials such as Fe—Mn, Pd—Mn, Pt—Mn, Pd—Pt—Mn, Ir—Mn, Rh—Mn, Ru—Mn and Cr—Mn—Pt may also be used to fabricate SV sensors according to the present invention. 
     It will also be apparent to those skilled in the art that alternative spacer layer  415  materials such as gold and silver may also be used to fabricate SV sensors according to the present invention. 
     It will be further apparent to those skilled in the art that alternative pinned layer  420  materials such as permalloy (Ni—Fe) and laminated multilayer films such as Ni—Fe/Co may be used to fabricate SV sensors according to the present invention. 
     While the present invention has been particularly shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit, scope and teaching of the invention. Accordingly, the disclosed invention is to be considered merely as illustrative and limited in scope only as specified in the appended claims.