Abstract:
A spin valve head according to the present invention includes a spin valve stack having a free layer, a first spacer layer, a pinned layer and a pinning layer. The spin valve stack is configured to operate in a current perpendicular to plane (CPP) mode, wherein a sense current flows substantially perpendicular to a longitudinal plane of the first spacer layer. The spin valve head includes a first shield and a second shield coupled to opposing sides of the spin valve stack. The first and the second shields act as electrodes to couple the sense current to the spin valve stack. The first shield has a concave shape and substantially surrounds the free layer. The spin valve head also includes a second spacer layer and a layer of antiferromagnetic material. The second spacer layer is formed on the free layer. The layer of antiferromagnetic material is formed on the second spacer layer.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of the filing date of U.S. Provisional Application Serial No. 60/193,560 entitled “CPP SPIN VALVE HEAD TO REDUCE THE SIDE READING AND IMPROVE MAGNETIC STABILITY”, which was filed Mar. 31, 2000. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to magnetoresistive read sensors for use in magnetic read heads. In particular, the present invention relates to a current perpendicular to plane (CPP) spin valve head with reduced side reading and improved magnetic stability. 
     A magnetic read head retrieves magnetically-encoded information that is stored on a magnetic medium or disc. The magnetic read head is typically formed of several layers that include a top shield, a bottom shield, and a read sensor positioned between the top and bottom shields. The read sensor is generally a type of magnetoresistive sensor, such as a giant magnetoresistive (GMR) read sensor. The resistance of a GMR read sensor fluctuates in response to a magnetic field emanating from a magnetic medium when the GMR read sensor is used in a magnetic read head and positioned near the magnetic medium. By providing a sense current through the GMR read sensor, the resistance of the GMR read sensor can be measured and used by external circuitry to decipher the information stored on the magnetic medium. 
     A common GMR read sensor configuration is the GMR spin valve configuration in which the GMR read sensor is a multi-layered structure formed of a ferromagnetic free layer, a ferromagnetic pinned layer and a nonmagnetic spacer layer positioned between the free layer and the pinned layer. The magnetization direction of the pinned layer is fixed in a predetermined direction, generally normal to an air bearing surface of the GMR spin valve, while a magnetization direction of the free layer rotates freely in response to an external magnetic field. An easy axis of the free layer is generally set normal to the magnetization direction of the pinned layer. The resistance of the GMR read sensor varies as a function of an angle formed between the magnetization direction of the free layer and the magnetization direction of the pinned layer. This multi-layered spin valve configuration allows for a more pronounced magnetoresistive effect than is possible with anisotropic magnetoresistive (AMR) read sensors, which generally consist of a single ferromagnetic layer. 
     Typically, the magnetization of the pinned layer is fixed in the predetermined direction by exchange coupling an antiferromagnetic layer to the pinned layer. The antiferromagnetic layer is positioned upon the pinned layer such that the antiferromagnetic layer and the free layer form distal edges of the GMR spin valve. The spin valve is then heated to a temperature greater than a Néel temperature of the antiferromagnetic layer. Next, a magnetic field oriented in the predetermined direction is applied to the spin valve, thereby causing the magnetization direction of the pinned layer to orient in the direction of the applied magnetic field. The magnetic field may be applied to the spin valve before the spin valve is heated to the temperature greater than the Néel temperature of the antiferromagnetic layer. While continuing to apply the magnetic field, the spin valve is cooled to a temperature lower than the Néel temperature of the antiferromagnetic layer. Once the magnetic field is removed from the spin valve, the magnetization direction of the pinned layer will remain fixed, as a result of the exchange with the antiferromagnetic layer, so long as the temperature of the spin valve remains lower than the Néel temperature of the antiferromagnetic layer. 
     The free layer of a spin valve sensor must be stabilized against the formation of edge domain walls because domain wall motion results in electrical noise, which makes data recovery impossible. A common way to achieve stabilization is with a permanent magnet abutted junction design. Permanent magnets have a high coercive field (i.e., are hard magnets). The field from the permanent magnets stabilizes the free layer and prevents edge domain formation, and provides proper bias. 
     However, there are several problems with permanent magnet abutted junctions. To properly stabilize the free layer, the permanent magnets must provide more flux than can be closed by the free layer. This undesirable extra flux stiffens the edges of the free layer so that the edges cannot rotate in response to flux from the media, and may also cause shield saturation which adversely affects the ability of the sensor to read high data densities. The extra flux from the permanent magnets may produce multiple domains in the free layer and may also produce dead regions which reduce the sensitivity of the sensor. For very small sensors, which are needed for high density recording, the permanent magnet bias severely reduces the sensitivity of the free layer. 
     Tabs of antiferromagnetic material or “exchange tabs” have also been used to stabilize the free layer of magnetic sensors. Exchange tabs are deposited upon the outer regions of the free layer and are exchange coupled thereto. Functions of the exchange tabs include pinning the magnetization of the outer regions of the free layer in the proper direction, preventing the formation of edge domains and defining the width of an active area of the free layer by preventing free layer rotation at the outer regions of the free layer. 
     Additional stabilization techniques are desirable, particular for ultra high density heads with small sensors. For 100 Gbit/in 2  and beyond magnetic recording storage, the track and linear densities are both very demanding. A typical design for a 100 Gbit/in 2  head should have a linear density of about 700 kilobits per inch (KBPI) and a track density of about 145 kilotracks per inch (KTPI). The written track cell for such a head is about 1,000 angstroms by 250 angstroms (i.e., an aspect ratio of about 4). High linear density requires a narrow shield-to-shield spacing. In order to meet the track density requirement, a small sensor size is needed (e.g., 0.1 by 0.1 micrometers). A larger sensor will produce side readings from adjacent tracks. 
     A novel design is needed to deal with such ultra-high density recording, while maintaining a stable free layer dynamic response and good cross-track characteristics. 
     BRIEF SUMMARY OF THE INVENTION 
     A spin valve head according to the present invention includes a spin valve stack having a free layer, a first spacer layer, a pinned layer and a pinning layer. The spin valve stack is configured to operate in a current perpendicular to plane (CPP) mode, wherein a sense current flows substantially perpendicular to a longitudinal plane of the first spacer layer. The spin valve head includes a first shield and a second shield coupled to opposing sides of the spin valve stack. The first and the second shields act as electrodes to couple the sense current to the spin valve stack. The first shield has a concave shape and substantially surrounds the free layer. The spin valve head also includes a second spacer layer and a layer of antiferromagnetic material. The second spacer layer is formed on the free layer. The layer of antiferromagnetic material is formed on the second spacer layer. 
     The spin valve head of the present invention senses ultra-high density recording, while maintaining a stable free layer dynamic response and good cross-track characteristics. The need for permanent magnet bias is eliminated, allowing a small sensor to be used to meet high track density requirements. The concave wrapped shield configuration reduces the side reading of the head. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a magnetic read/write head and magnetic disc taken along a plane normal to an air bearing surface of the read/write head. 
     FIG. 2 is a layer diagram of an air bearing surface of a magnetic read/write head. 
     FIG. 3 is a perspective view of a prior art GMR stack. 
     FIG. 4 is a perspective view of a prior art GMR spin valve stack with permanent magnet abutted junctions. 
     FIG. 5A shows an ABS view of a CPP type of spin valve according to the present invention. 
     FIG. 5B shows a cross-sectional view of a CPP type of spin valve according to the present invention. 
     FIG. 6A shows an ABS view of a second embodiment of a CPP type of spin valve according to the present invention, which provides additional shielding of the free layer. 
     FIG. 6B shows a cross-sectional view of a second embodiment of a CPP type of spin valve according to the present invention, which provides additional shielding of the free layer. 
     FIG. 7 shows typical M-H loops of an exchange biased NiFe free layer with a structure NiFe/Cu(10 Å)/IrMn. 
     FIG. 8 shows a graph of GMR, R and dR versus thickness of a Cu spacer layer in a spin valve with IrMn free layer stabilization. 
     FIG. 9 shows a graph of interlayer coupling (H 1 ) and effective H k  for a spin valve with IrMn free layer stabilization. 
     FIG. 10 shows a graph of R and dR versus hard axis field for a spin valve with IrMn free layer stabilization. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a cross-sectional view of magnetic read/write head  100  and magnetic disc  102  taken along a plane normal to air bearing surface  104  of read/write head  100 . Air bearing surface  104  of magnetic read/write head  100  faces disc surface  106  of magnetic disc  102 . Magnetic disc  102  travels or rotates in a direction relative to magnetic read/write head  100  as indicated by arrow A. Spacing between air bearing surface  104  and disc surface  106  is preferably minimized while avoiding contact between magnetic read/write head  100  and magnetic disc  102 . 
     A writer portion of magnetic read/write head  100  includes top pole  108 , insulator layer  110 , conductive coils  112  and top shield  114 . Conductive coils  112  are held in place between top pole  108  and top shield  114  by use of insulator  110 . Conductive coils  112  are shown in FIG. 1 as two layers of coils but may also be formed of more layers of coils as is well known in the field of magnetic read/write head design. 
     A reader portion of magnetic read/write head  100  includes top shield  114 , top gap layer  115 , metal contact layer  116 , bottom gap layer  117 , bottom shield  118 , and giant magnetoresistive (GMR) stack  120 . Metal contact layer  116  is positioned between top gap layer  115  and bottom gap layer  117 . GMR stack  120  is positioned between terminating ends of metal contact layer  116  and bottom gap layer  117 . Top gap layer  115  is positioned between top shield  114  and metal contact layer  116 . Bottom gap layer  117  is positioned between metal contact layer  116  and bottom shield  118 . Top shield  114  functions both as a shield and as a shared pole for use in conjunction with top pole  108 . 
     FIG. 2 is a layer diagram of air bearing surface  104  of magnetic read/write head  100 . FIG. 2 illustrates the location of magnetically significant elements in magnetic read/write head  100  as they appear along air bearing surface  104  of magnetic read/write head  100  of FIG.  1 . In FIG. 2, all spacing and insulating layers of magnetic read/write head  100  are omitted for clarity. Bottom shield  118  and top shield  114  are spaced to provide for a location of GMR stack  120 . GMR stack  120  has two passive regions defined as the portions of GMR stack  120  adjacent to metal contact layer  116 . An active region of GMR stack  120  is defined as the portion of GMR stack  120  located between the two passive regions of GMR stack  120 . The active region of GMR stack  120  defines a read sensor width. 
     FIG. 3 is a perspective view of a prior art GMR stack  130 . GMR stack  130  has free layer  132 , spacer layer  134 , pinned layer  136 , and antiferromagnetic layer  138 . Spacer layer  134  is positioned between free layer  132  and pinned layer  136 . A magnetization of pinned layer  136  is fixed in a predetermined direction, generally normal to air bearing surface  140  of GMR stack  130 , while a magnetization of free layer  132  rotates freely in response to an external magnetic field (not shown in FIG.  3 ). Antiferromagnetic layer  138  is positioned on GMR stack  130  such that pinned layer  136  is between spacer layer  134  and antiferromagnetic layer  138 . The magnetization of pinned layer  136  is pinned by exchange coupling pinned layer  136  with antiferromagnetic layer  138 . 
     The resistance of GMR stack  130  varies as a function of an angle that is formed between the magnetization of pinned layer  136  and the magnetization of free layer  132 . The magnetization of pinned layer  136  remains fixed in one direction, while the magnetization of free layer  132  rotates in response to a magnetic field emanating from a magnetic media or disc. The angle formed between the magnetization of free layer  132  and the magnetization of pinned layer  136  is, therefore, directly related to the magnetic field emanating from a magnetic media or disc. Consequently, the resistance of GMR stack  130  is directly related to the magnetic field emanating from the magnetic media or disc. 
     FIG. 4 is a perspective view of prior art GMR spin valve stack  142  with permanent magnet abutted junctions. GMR stack  142  includes permanent magnets  145 A and  145 B, pinning layer  146 , pinned layer  147 , spacer layer  148  and free layer  149 . Pinned layer  147  is positioned over pinning layer  146 . Spacer layer  148  is positioned over pinned layer  147 . Free layer  149  is positioned over spacer layer  148 . Permanent magnets  145 A and  145 B are placed on each side of GMR stack  142 . Junction  144 A is located between permanent magnet  145 A and a first edge of layers  146 - 149 . Junction  144 B is positioned between permanent magnet  145 B and a second edge of layers  146 - 149 . 
     The field from permanent magnets  145 A and  145 B stabilizes free layer  149  and prevents edge domain formation, and provides proper bias. However, there are several problems with the permanent magnet abutted junction design shown in FIG.  4 . To properly stabilize free layer  149 , permanent magnets  145 A and  145 B must provide more flux than can be closed by free layer  149 . This undesirable extra flux stiffens the edges of free layer  149  and may also cause shield saturation. The extra flux from permanent magnets  145  may produce multiple domains in free layer  149  and may also produce dead regions which reduce the sensitivity of the sensor. These undesirable effects are particularly problematic for very small sensors, which are needed for high density recordings. 
     FIG. 5A shows an ABS view of a CPP type of spin valve according to the present invention. Spin valve head  150  includes top shield  152 , insulation layers  154 A and  154 B, bias layer  156 , spacer layer  158 , free layer  160 , second spacer layer  162 , pinned layer  163 , pinning layer  170 , seed layer  172  and bottom shield  174 . Top shield  152  also acts as a shared pole in merged read/write heads. Bias layer  156  is preferably IrMn, PtMn, NiMn, RhMn, RuRhMn or similar antiferromagnetic material. Spacer layers  158  and  162  are preferably Cu, although other materials including Au, Ag, NiFeCr, Al and Ru can alternatively be used. Free layer  160  is a ferromagnetic layer such as NiFe. The magnetization of free layer  160  is shown by an arrow on that layer. Pinned layer  163  is a synthetic antiferromagnet or SAF, and includes first CoFe layer  164 , Ru spacer layer  166  and second CoFe layer  168 . When two ferromagnetic layers, such as CoFe layers  164  and  168  are separated by an Ru spacer of an appropriate thickness, the two ferromagnetic layers couple strongly with magnetic moments anti-parallel as shown by the circled “X” (into the paper) and circled dot (out of the paper) on these layers. The use of a synthetic antiferromagnet for pinned layer  163  provides a reduced demagnetization field, and provides better magnetic stability. Alternatively, pinned layer  163  could be a single soft magnetic layer, such as CoFe. Pinning layer  170  is preferably IrMn, PtMn, NiMn, RhMn, RuRhMn or similar antiferromagnetic material. Insulation layers  154 A and  154 B are preferably alumina or SiO 2 . 
     Top shield  152  has a concave shape and is wrapped around free layer  160 . Since there are no permanent magnet layers positioned adjacent to the edges of free layer  160 , top shield  152  may be positioned close to the ends of free layer  160  and thereby reduce any side reading. A reduction in the side reading helps to improve the TPI resolution of spin valve head  150 . Top shield  152  and bottom shield  174  act as electrodes for conducting a sense current. The sense current flows between top shield  152  and bottom shield  174  and through layers  156 - 172 . This mode of operation, where the sense current flows perpendicular to the plane of spacer layer  162 , is referred to as current perpendicular to plane or CPP mode. Operation in CPP mode provides an enhanced GMR response. 
     Layers  156 - 164  include end regions  155 A and  155 B. Since the area near end regions  155 A and  155 B is free of any metallic layers, like contact and permanent magnet layers, the ends of free layer  160  may be positioned close to top shield  152 , which confines the bit flux lateral conduction and reduces the side reading when head  150  is off track. 
     Layers  156  and  158  serve to stabilize free layer  160 , as well as to improve the GMR ratio due to the spin filter effect. The spin filter effect refers to the increase in GMR caused by positioning the free layer between two copper layers, and thereby creating two copper layer/free layer interfaces. 
     The antiferromagnetic materials used for layers  156  and  170  preferably have a high blocking temperature. However, since layer  156  is in contact with shield  152 , which is highly conductive, the requirement of a high blocking temperature is relaxed. 
     FIG. 5B shows a cross-sectional view of spin valve head  150 . As shown in FIG. 5B, top lead  159 A includes top shield  152 , bias layer  156  and spacer layer  158 . Bottom lead  159 B includes Ru spacer layer  166 , CoFe layer  168 , pinning layer  170 , seed layer  172  and bottom shield  174 . The magnetizations of CoFe layers  164  and  168  are indicated by arrows, and the magnetization of free layer  160  is out of the paper as indicated by the circled dot on that layer. 
     FIG. 6A shows an ABS view of a second embodiment of a CPP type of spin valve according to the present invention, which provides additional shielding of the free layer. CPP spin valve  180  includes top shield  182 , bias layer  156 , spacer layer  185 , free layer  160 , second spacer layer  162 , pinned layer  189 , pinning layer  190 , seed layer  192 , insulation layers  184 A and  184 B, and bottom shield  174 . Pinned layer  189  is a synthetic antiferromagnet, and includes first CoFe layer  164 , Ru spacer layer  186  and second CoFe layer  188 . The sensor stack includes end regions  193 A and  193 B. By cutting the entire sensor stack such that all of the layers of the stack line up as shown in FIG. 6A (rather than cutting just the top  5  layers as shown in FIG.  5 A), top shield  182  may be wrapped around additional layers of the stack and thereby provide further shielding of the sensor stack. Furthermore, since no GMR layer is beyond the physical track width, the side reading is reduced. 
     FIG. 6B shows a cross-sectional view of spin valve head  180 . Spin valve head  180  has a different lead configuration than the embodiment shown in FIG.  5 B. Top lead  183 A includes top shield  182  and bias layer  156 . Bottom lead  183 B includes pinning layer  190 , seed layer  192  and bottom shield  174 . The magnetizations of CoFe layers  164  and  188  are indicated by arrows, and the magnetization of free layer  160  is out of the paper as indicated by the circled dot on that layer. 
     The sensitivity of free layer  160  can be adjusted to a desirable value using layers  156  and  185 . Free layer  160  should be pinned to a certain degree to ensure stability, but must also be allowed to rotate in response to flux from magnetic media. When an antiferromagnetic layer (like bias layer  156 ) is coupled to a ferromagnetic layer (like free layer  160 ), the ferromagnetic layer has an induced anisotropy along the unidirectional exchange coupling field direction, which is characterized by an open hysteresis loop with an offset from zero field. FIG. 7 shows an example of such a loop. One-half of the width of hysteresis loop  200  is referred to as the coercivity, or H c . The amount that hysteresis loop  200  is offset from the zero field point is represented by H ex , which is the exchange field or pinning field. Bias layer  156  preferably provides a pinning field in a direction parallel to the ABS, although the pinning field may alternatively be canted away from the ABS at an angle of, for example, 10 degrees. 
     FIG. 7 also shows hard axis loop  202 , which is very closed with a purely rotational reversal process. The hard axis is perpendicular to the pinning field. The hard axis anisotropy field, H k , is the field magnitude that is needed to drive the ferromagnetic layer (e.g., free layer  160 ) into saturation along the hard axis. In FIG. 7, the value of H k  is given by the intersection of line  204  with easy axis loop  200 . Line  204  is tangent to hard axis loop  202 . H k  is approximately equal to H ex +H c  along the easy axis (i.e., along the pinning field). The sum of H ex  and Hc is referred to as the effective Hk. The permeability of an exchange biased soft magnetic layer is inversely proportional to the effective H k . 
     By introducing a highly conductive metallic layer like Cu between layers  156  and  160 , the exchange field (H ex ), the effective H k  and the permeability can be finely tuned to a desirable value. The following three tables show the exchange field, coercivity and H k  for IrMn, PtMn, and NiMn antiferromagnets coupled to a NiFe layer with a varying thickness Cu spacer layer. Data are shown for two cases—as made, and after annealing. 
     
       
         
               
             
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 (IrMn/Cu/NiFe) 
               
             
          
           
               
                   
                 As-made 
                 Annealed 
               
             
          
           
               
                 Cu layer (Å) 
                 H ex   
                 H c   
                 H k   
                 H ex   
                 H c   
                 H k   
               
               
                   
               
             
          
           
               
                 0 
                 38.6 
                 2.2 
                 40 
                 24 
                 3.1 
                 27 
               
               
                 5 
                 16.2 
                 2.3 
                 15 
                 9.1 
                 2.9 
                 13 
               
               
                 10 
                 3.9 
                 1.6 
                 5.5 
                 2.8 
                 2.2 
                 5.9 
               
               
                 15 
                 0.9 
                 1.2 
                 3.0 
                 0.8 
                 1.8 
                 2.9 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 (PtMn/Cu/NiFe) 
               
             
          
           
               
                   
                 As-made 
                 Annealed 
               
             
          
           
               
                 Cu layer (Å) 
                 H ex   
                 H c   
                 H k   
                 H ex   
                 H c   
                 H k   
               
               
                   
               
             
          
           
               
                 0 
                   
                   
                   
                 168 
                 155 
                 300 
               
               
                 5 
                   
                   
                   
                 142 
                 110 
                 260 
               
               
                 10 
                   
                   
                   
                  93 
                  60 
                 150 
               
               
                 15 
                   
                   
                   
                  50 
                  35 
                  80 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
             
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 (NiMn/Cu/NiFe) 
               
             
          
           
               
                   
                 As-made 
                 Annealed 
               
             
          
           
               
                 Cu layer (Å) 
                 H ex   
                 H c   
                 H k   
                 H ex   
                 H c   
                 H k   
               
               
                   
               
             
          
           
               
                 0 
                 15.8 
                 4.9 
                 20 
                 241 
                 150 
                 395 
               
               
                 5 
                 12.8 
                 3.5 
                 16 
                 212 
                 135 
                 350 
               
               
                 10 
                 1.99 
                 1.7 
                 3.7 
                 149 
                 110 
                 260 
               
               
                 15 
                 0.79 
                 1.7 
                 2.6 
                  90 
                  70 
                 160 
               
               
                   
               
             
          
         
       
     
     No data is shown above for the “As-made” case for PtMn because annealing is required to induce pinning for this material. It is clear from the above tables that the effective H k  can be adjusted. It is also evident from the above tables that annealing can be used to modify and further optimize the sensitivity of free layer  160 . In the finished head, the sensitivity of free layer  160  is dominated by the shape anisotropy of free layer  160 , which is proportional to mst/h. The letters “ms” in “mst/h” represent the saturation magnetization of free layer  160 , “t” represents the thickness of free layer  160 , and “h” represents the stripe height. The exchange coupling induced anisotropy is a small term in the effective anisotropy. 
     FIGS. 8-10 show test data for an IrMn stabilization layer  156  exchange coupled to free layer  160 . Two annealing steps are used to set the magnetizations of spin valve  150 . A first anneal is used to induce magnetization of pinned layer  163  perpendicular to the ABS. A second anneal, referred to as a cross anneal, is used to induce magnetization of free layer  160  parallel to the ABS. The cross anneal is preferably done at 250 C. for two hours, although other times and temperatures may be used. The stabilization field is, therefore, perpendicular to the pinning field. 
     FIG. 8 shows a graph of GMR, R and dR versus thickness of spacer layer  158  in spin valve  150  with IrMn free layer stabilization. As shown in FIG. 8, GMR is almost constant, and both dR and R decrease with increasing thickness of spacer layer  158 . 
     FIG. 9 shows a graph of interlayer coupling (H 1 ) and effective Hk (actually 2 H K   *  or two times the effective H k ) for a spin valve  150  with IrMn free layer stabilization. H 1  and effective H k  both decrease with increasing thickness of spacer layer  158 . 2 H K   *  is approximately 480 Oe when IrMn stabilization layer  156  is in direct contact with free layer  160 . 2 H K * decreases (and the slope of the R-H curve increases) dramatically with increasing thickness of spacer layer  158 . Interlayer coupling (H 1 ) between free layer  160  and stabilization layer  156  was measured along the hard axis. The hard axis is parallel to the ABS and the easy axis is perpendicular to the ABS. H 1  measures the field shift of the hard axis loop when the resistance reaches a minimum. The resistance is a minimum when the magnetizations of free layer  160  and pinned layer  163  are aligned. A magnetic field is applied along the hard axis in the opposite direction of the stabilization field. When the applied magnetic field is equal to the stabilization field, there is zero net magnetic field along the ABS direction, the magnetization of free layer  160  aligns with that of pinned layer  163 , and the resistance reaches a minimum. 
     Effective H k  in FIG. 9 was obtained by applying a field along the easy axis. Effective H k  is given by the field width of the sloped region of the R-H curve (see FIG.  10 ). Because of the stabilization field along the hard axis, it is more difficult to rotate free layer  160  along the easy axis. This effect is referred to as the effective H k . 
     FIG. 10 shows a graph of R and dR versus hard axis field for a spin valve  150  with IrMn stabilization of free layer  160 . Free layer  160  follows a rotational path with no hysteresis. For all values of Cu spacer  158  thickness, the Hc of free layer  160  measured along the hard axis direction is very narrow (less than 1 Oe under an applied field of 100 Oe). 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, the spin valve sensor can be either a top or a bottom spin valve stack. The shield that wraps around the spin valve stack can either be the top shield or the bottom shield, and a different contact lead layout can be used to reduce the lead resistance. Other modifications are also possible.