Abstract:
A spin valve sensor is provided with a free layer structure which is located between first and second AP pinned layer structures wherein the first AP pinned layer structure includes first and second AP pinned layers and the second AP pinned layer structure includes first, second and third AP pinned layers. With this arrangement the magnetic spins of first and second pinning layers exchange coupled to the first and second AP pinned layer structures can be set by a current pulse conducted through a sense current circuit which sufficiently raises the temperature of the first and second pinning layers and exerts sense current fields appropriately directed to cause the setting of the magnetic spins of the first and second pinning layers. This arrangement allows the spin valve sensor to be reset in a magnetic disk drive without the application of a field from an exterior source in the presence of heat from an exterior source.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a read head with a file resettable double antiparallel (AP) pinned spin valve sensor and more particularly to a spin valve sensor wherein a current pulse is employed for resetting magnetic spins of first and second pinnning layers that pin first and second AP pinned layer structures of the spin valve sensor. 
     2. Description of the Related Art 
     A spin valve sensor is employed by a read head for sensing magnetic fields on a moving magnetic medium, such as a rotating magnetic disk. A typical sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning a magnetic moment of the pinned layer 90° to an air bearing surface (ABS) which is an exposed surface of the sensor that faces the magnetic medium. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. A magnetic moment of the free layer is free to rotate in positive and negative directions from a quiescent or bias point position in response to positive and negative magnetic field signals from a rotating magnetic disk. The quiescent position, which is typically parallel to the ABS, is the position of the magnetic moment of the free layer with the sense current conducted through the sensor in the absence of signal fields. If the quiescent position of the magnetic moment is not parallel to the ABS in the absence of a signal field the positive and negative responses of the free layer to positive and negative signal fields will not be equal which results in read signal asymmetry which is discussed in more detail hereinbelow. 
     The thickness of the spacer layer is chosen so that shunting of the sense current and a magnetic coupling between the free and pinned layers are minimized. This thickness is typically less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons are scattered at the interfaces of the spacer layer with respect to the pinned and free layers. When the magnetic moments of the pinned and free layers are parallel with respect to one another scattering is at. a minimum and when their magnetic moments are antiparallel scattering is maximized. Changes in scattering in response to signal fields from a rotating disk changes the resistance of the spin valve sensor as a function of cos θ, where θ is the angle between the magnetic moments of the pinned and free layers. The sensitivity of the sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in resistance of the sensor between parallel and antiparallel orientations of the pinned and free layers and R is the resistance of the sensor when the moments are parallel. 
     The transfer curve (readback signal of the spin valve head versus applied signal from the magnetic disk) of a spin valve sensor is a substantially linear portion of the aforementioned function of cos θ. The greater this angle, the greater the resistance of the spin valve to the sense current and the greater the readback signal (voltage sensed by processing circuitry). With positive and negative signal fields from a rotating magnetic disk (assumed to be equal in magnitude), it is important that positive and negative changes of the resistance of the spin valve sensor be equal in order that the positive and negative magnitudes of the readback signals are equal. When this occurs a bias point on the transfer curve is considered to be zero and is located midway between the maximum positive and negative readback signals. When the direction of the magnetic moment of the free layer is parallel to the ABS, and the direction of the magnetic moment of the pinned layer is perpendicular to the ABS in a quiescent state (absence of signal fields) the bias point is located at zero and the positive and negative readback signals will be equal when sensing positive and negative signal fields from the magnetic disk. The readback signals are then referred to in the art as having symmetry about the zero bias point. When the readback signals are not equal the readback signals are asymmetric which equates to reduced storage capacity. 
     The location of the bias point on the transfer curve is influenced by three major forces on the free layer, namely a demagnetization field (H D ) from the pinned layer, a ferromagnetic coupling field (H F ) between the pinned layer and the free layer, and sense current fields (H I ) from all conductive layers of the spin valve except the free layer. When the sense current is conducted through the spin valve sensor, the pinning layer (if conductive), the pinned layer and the first spacer layer, which are all on one side of the free layer, impose sense current fields on the free layer that rotate the magnetic moment of the free layer in a first direction. The ferromagnetic coupling field from the pinned layer further rotates the magnetic moment of the free layer in the first direction. The demagnetization field from the pinned layer on the free layer rotates the magnetic moment of the free layer in a direction opposite to the first direction. Accordingly, the demagnetization field opposes the sense current and ferromagnetic coupling fields and can be used for counterbalancing. 
     In some spin valve sensors an antiparallel (AP) pinned layer structure is substituted for the typical single layer pinned layer. The AP pinned layer structure includes a nonmagnetic AP coupling layer between first and second AP pinned layers. The first AP pinned layer is exchange coupled to the antiferromagnetic pinning layer which pins the magnetic moment of the first AP pinned layer in the same direction as the magnetic spins of the pinning layer. By exchange coupling between the first and second AP pinned layers the magnetic moment of the second AP pinned layer is pinned antiparallel to the magnetic moment of the first AP pinned layer. An advantage of the AP pinned layer structure is that demagnetization fields of the first and second AP pinned layers partially counterbalance one another so that a small demagnetization field is exerted on the free layer for improved biasing of the free layer. Further, the first AP pinned layer can be thinner than the single pinned layer which increases an exchange coupling field between the pinning layer and the first AP pinned layer. 
     In both the single pinned layer and the AP pinned layer type of spin valve sensor the magnetic spins of the pinning layer are set by applying a field from an exterior source in the presence of heat from an exterior source. This is typically accomplished at the wafer and/or row level in the construction of multiple magnetic heads arranged in rows and columns on a wafer. It is not practical to employ this process to reset the magnetic spins of the pinning layer at the file level magnetic head mounted in a magnetic disk drive because of a degradation of the head components by the applied heat. If the magnetic spins of the pinning layer become disoriented at the file level the disk drive may be rendered inoperable. 
     Over the years a significant amount of research has been conducted to improve symmetry of the read signals, the magnetoresistive coefficient dr/R and the read gap. The read gap, which is the distance between the first and second shield layers, should be minimized to increase the linear bit reading density of the read head. These efforts have increased the storage capacity of computers from kilobytes to megabytes to gigabytes. 
     SUMMARY OF THE INVENTION 
     I have provided a spin valve sensor which has improved magnetoresistive coefficient dr/R, improved read signal symmetry, a narrower gap and which can be reset in a magnetic disk drive in contrast to being reset at the wafer or row level. This has been accomplished by providing first and second AP pinned structures with the first AP pinned structure being on one side of the free layer and separated therefrom by a first spacer layer and a second AP pinned structure on the other side of the free layer and separated therefrom by a second spacer layer. The first AP pinned structure has first and second AP pinned layers that are separated by an AP coupling layer and the second AP pinned structure has first, second and third AP pinned layers that are separated by first and second AP coupling layers. With this arrangement the first AP pinned layer of the first AP pinned structure and the third AP pinned layer of the second AP pinned structure interface the first and second spacer layers and have their magnetic moments in phase which means that they are parallel with respect to one another. Accordingly, as the magnetic moment of the free layer is rotated upwardly or downwardly in response to signal fields a double spin valve effect is obtained on each side of the free layer which are additive to significantly increase the magnetoresistive coefficient dr/R of this spin valve sensor as compared to a simple spin valve sensor with a pinned structure only on one side of the free layer. 
     Read signal symmetry is easier to obtain with the present spin valve sensor. Since the magnetic moments of the AP pinned layers that interface the first and second spacer layers are in phase ferromagnetic coupling fields between these AP pinned layers and the free layer will be additive which exert a force to rotate the magnetic moment of the free layer in one direction. Each of the pinned layer structures have a net demagnetization field that is exerted on the free layer. However, these demagnetization fields are in opposite directions and can be made to completely counterbalance one another or provide a net demagnetization field which helps to counterbalance the ferromagnetic coupling fields. If the net demagnetization field from each of the AP pinned structures are equal so as to counterbalance one another an extra thickness of the metallic layers of the triple AP pinned structure may be employed for providing a sense current field which counterbalances the ferromagnetic coupling fields on the free layer. The present spin valve sensor provides many options for positioning the magnetic moment of the free layer so that the free layer operates from the zero bias point on its transfer curve in a quiescent condition. 
     The present spin valve sensor also provides a very significant advantage in setting or resetting the magnetic spins of first and second antiferromagnetic pinning layers which are exchange coupled to the first and second AP pinned structures. A current pulse can be conducted by a sense current circuit through the spin valve sensor for setting the magnetic spins of the first and second pinning layers. I have found that a voltage pulse of approximately 1.0 volt, which is approximately three times the sense voltage Vs, for a period of approximately 100 nanoseconds (ns) is sufficient for raising the temperature of the pinning layers and providing sense current fields on the AP pinned structures which causes the magnetic spins of the first and second pinning layers to be oriented in the desired directions. This type of setting is in contrast to the prior art method of setting where a field from an exterior source in the presence of a temperature from an exterior source is employed for resetting the magnetic spins of the pinning layers. With the present spin valve sensor the magnetic spins of the pinning layers can be reset in a magnetic disk drive which is referred to hereinafter as file resettable. In order to keep the required temperature low for resetting I employ a material for each of the first and second pinning layers that has a blocking temperature below 280° C. Materials can be selected from the group comprising iridium manganese (IrMn), nickel oxide (NiO) and iron manganese (FeMn) with the preferred material being iridium manganese (IrMn). Blocking temperature is the temperature at which the magnetic spins of the antiferromagnetic pinning layer are free to rotate in response to an applied field. Iridium manganese (IrMn) has a blocking temperature of 250° C. to 260° C. Significantly, however, is that only 60 Å to 80 Å of iridium manganese (IrMn) is required to function as a pinning layer as compared to nickel oxide (NiO) which is required to be approximately 425 Å in order to function as a pinning layer. Accordingly, in a preferred embodiment each of the first and second pinning layers in the present invention is iridium manganese (IrMn) which promotes a narrow gap for the read head. As stated hereinabove, a narrow gap equates to increased storage capacity of the magnetic disk drive. 
     An object of the present invention is to provide a spin valve sensor which has improved magnetoresistive coefficient dr/R, improved read signal symmetry, a narrower gap and which can be reset in a magnetic disk drive. 
     Another object is to provide a file resettable spin valve sensor that has a double AP pinned structure. 
     Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of an exemplary magnetic disk drive; 
     FIG. 2 is an end view of a slider with a magnetic head of the disk drive as seen in plane  2 — 2 ; 
     FIG. 3 is an elevation view of the magnetic disk drive wherein multiple disks and magnetic heads are employed; 
     FIG. 4 is an isometric illustration of an exemplary suspension system for supporting the slider and magnetic head; 
     FIG. 5 is an ABS view of the slider taken along plane  5 — 5  of FIG. 2; 
     FIG. 6 is a partial view of the slider and a piggyback magnetic head as seen in plane  6 — 6  of FIG. 2; 
     FIG. 7 is a partial view of the slider and a merged magnetic head as seen in plane  7 — 7  of FIG. 2; 
     FIG. 8 is a partial ABS view of the slider taken along plane  8 — 8  of FIG. 6 to show the read and write elements of the piggyback magnetic head; 
     FIG. 9 is a partial ABS view of the slider taken along plane  9 — 9  of FIG. 7 to show the read and write elements of the merged magnetic head; 
     FIG. 10 is a view taken along plane  10 — 10  of FIGS. 6 or  7  with all material above the coil layer and leads removed; 
     FIG. 11 is an isometric ABS illustration of a prior art read head which employs a spin valve sensor longitudinally biased by hard biasing layers; 
     FIG. 12 is an ABS illustration of the present spin valve sensor; 
     FIG. 13 is a side view of the present spin valve sensor after FIG. 12 has been rotated 90° clockwise and 90° toward the viewer; 
     FIG. 14 is the same as FIG. 13 except different sense current fields are illustrated; and 
     FIG. 15 is the same as FIG. 12 except the order of the layers has been reversed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Magnetic Disk Drive 
     Referring now to the drawings wherein like reference numerals designate like or similar parts throughout the several views, FIGS. 1-3 illustrate a magnetic disk drive  30 . The drive  30  includes a spindle  32  that supports and rotates a magnetic disk  34 . The spindle  32  is rotated by a spindle motor  36  that is controlled by a motor controller  38 . A slider  42  supports a combined read and write magnetic head  40  and is supported by a suspension  44  and actuator arm  46  which is rotatably positioned by an actuator  47 . A plurality of disks, sliders and suspensions may be employed in a large capacity direct access storage device (DASD) as shown in FIG.  3 . The actuator  47  moves the actuator arm  46  and the suspension  44  to position the slider  42  so that the magnetic head  40  is in a transducing relationship with a surface of the magnetic disk  34 . When the disk  34  is rotated by the spindle motor  36  the slider is supported on a thin (typically,  0 . 05  μm) cushion of air (air bearing) between the surface of the disk  34  and the air bearing surface (ABS)  48 . The magnetic head  40  may then be employed for writing information to multiple circular tracks on the surface of the disk  34 , as well as for reading information therefrom. Processing circuitry  50  exchanges signals, representing such information, with the head  40 , provides spindle motor drive signals for rotating the magnetic disk  34 , and provides control signals to the actuator  47  for moving the slider to various tracks. In FIG. 4 the slider  42  is shown mounted to a suspension  44 . The components described hereinabove may be mounted on a frame  54  of a housing  55 , as shown in FIG.  3 . 
     FIG. 5 is an ABS view of the slider  42  and the magnetic head  40 . The slider has a center rail  56 , which supports the magnetic head  40 , and side rails  58  and  60 . The rails  56 ,  58  and  60  extend from a cross rail  62 . With respect to rotation of the magnetic disk  34 , the cross rail  62  is at a leading edge  64  of the slider and the magnetic head  40  is at a trailing edge  66  of the slider. 
     FIG. 6 is a side cross-sectional elevation view of a piggyback magnetic head  40 , which includes a write head portion  70  and a read head portion  72 , the read head portion employing a spin valve sensor  74  of the present invention. FIG. 8 is an ABS view of FIG.  6 . The spin valve sensor  74  is sandwiched between nonmagnetic electrically insulative first and second read gap layers  76  and  78 , and the read gap layers are sandwiched between ferromagnetic first and second shield layers  80  and  82 . In response to external magnetic fields, the resistance of the spin valve sensor  74  changes. A sense current I s  conducted through the sensor causes these resistance changes to be manifested as potential changes. These potential changes are then processed as readback signals by the processing circuitry  50  shown in FIG.  3 . 
     The write head portion  70  of the magnetic head  40  includes a coil layer  84  sandwiched between first and second insulation layers  86  and  88 . A third insulation layer  90  may be employed for planarizing the head to eliminate ripples in the second insulation layer caused by the coil layer  84 . The first, second and third insulation layers are referred to in the art as an “insulation stack”. The coil layer  84  and the first, second and third insulation layers  86 ,  88  and  90  are sandwiched between first and second pole piece layers  92  and  94 . The first and second pole piece layers  92  and  94  are magnetically coupled at a back gap  96  and have first and second pole tips  98  and  100  which are separated by a write gap layer  102  at the ABS. An insulation layer  103  is located between the second shield layer  82  and the first pole piece layer  92 . Since the second shield layer  82  and the first pole piece layer  92  are separate layers this head is known as a piggyback head. As shown in FIGS. 2 and 4, first and second solder connections  104  and  106  connect leads from the spin valve sensor  74  to leads  112  and  114  on the suspension  44 , and third and fourth solder connections  116  and  118  connect leads  120  and  122  from the coil  84  (see FIG. 10) to leads  124  and  126  on the suspension. 
     FIGS. 7 and 9 are the same as FIGS. 6 and 8 except the second shield layer  82  and the first pole piece layer  92  are a common layer. This type of head is known as a merged magnetic head. The insulation layer  103  of the piggyback head in FIGS. 6 and 8 is omitted. 
     FIG. 11 is an isometric ABS illustration of a prior art read head  72  which has a spin valve sensor  130 . The spin valve sensor  130  has a pinned layer structure, to be described hereinafter, which has a magnetic moment that is pinned by an antiferromagnetic (AFM) pinning layer  132 . First and second hard bias and lead layers  134  and  136  are connected to first and second side edges  138  and  140  of the spin valve sensor. This connection is known in the art as a contiguous junction and is fully described in commonly assigned U. S. Pat. 5,018,037. The first hard bias and lead layers  134  include a first hard bias layer  141  and a first lead layer  142  and the second hard bias and lead layers  136  include a second hard bias layer  144  and a second lead layer  146 . The hard bias layers  140  and  144  cause magnetic flux to extend longitudinally through the spin valve sensor  130  for stabilizing magnetic domains of the free layer. The spin valve sensor  130  and the first and second hard bias and lead layers  134  and  136  are located between nonmagnetic electrically insulative first and second read gap layers  148  and  150 . The first and second read gap layers  148  and  150  are, in turn, located between first and second shield layers  152  and  154 . 
     The Invention 
     FIG. 12 illustrates the present spin valve sensor  200  which has a free layer structure  202  which is located between first and second AP pinned layer structures  204  and  206 . In a preferred embodiment the free layer structure  202  has a nickel iron (NiFe) free layer (F)  208  which is located between first and second cobalt (Co) based nanolayers (N)  210  and  212 . The free layer structure  202  has a magnetic moment  208  which is substantially parallel to the ABS, either from right to left, or from left to right as shown in FIG. 12. A first spacer layer (S)  214  is located between the first AP pinned layer structure  204  and the free layer structure  202  and a second spacer layer (S)  216  is located between the second AP pinned layer structure  206  and the free layer structure. 
     The first AP pinned layer structure  204  includes an antiparallel coupling layer  218  which is located between first and second AP pinned layers (AP1) and (AP2)  220  and  222 . The second AP pinned layer structure  206  includes a first AP coupling layer  224  which is located between first and second AP pinned layers (AP1 ) and (AP 2)  226  and  228  and a second AP coupling layer  230  which is located between the second AP pinned layer  228  and a third AP pinned layer (AP3)  232 . Accordingly, the first AP pinned layer structure  204  has two ferromagnetic layers  220  and  222  and the second AP pinned layer structure  206  has three ferromagnetic layers  226 ,  228  and  232 . A first antiferromagnetic (AFM) pinning layer  234  is exchange coupled to the first AP pinned layer  220  which may set a magnetic moment  236  of the first AP pinned layer perpendicular to and away from the ABS as shown in FIG.  12 . By antiparallel coupling between the first and second AP pinned layers  220  and  222  a magnetic moment  238  of the second AP pinned layer is oriented antiparallel to the magnetic moment  236 . A second antiferromagnetic (AFM) pinning layer  240  is exchange coupled to the first AP pinned layer  226  which may pin a magnetic moment  242  of the first AP pinned layer perpendicular to and toward the ABS as shown in FIG.  12 . By antiparallel coupling between the first and second AP pinned layers  226  and  228  a magnetic moment  244  of the second AP pinned layer  228  is oriented perpendicular to and away from the ABS and by antiparallel coupling between the second and third AP pinned layers  228  and  232  a magnetic moment  246  of the third AP pinned layer is oriented perpendicular to and toward the ABS as shown in FIG.  12 . 
     With the above arrangement the orientations of the magnetic moments  238  and  246  are parallel with respect to one another which means they are in phase. This is required for the spin valve effect on each side of the free layer structure  202  to be additive. If a signal field causes the magnetic moment  208  of the free layer structure to rotate upwardly the resistance of the spin valve sensor will increase in the sense current circuit which conducts the sense current I s  and if a signal field causes the magnetic moment  208  to rotate downwardly the resistance will decrease in the sense current circuit. These increases and decreases in the resistances of the spin valve sensor in response to signal fields are manifested as potential changes in the sense current circuit which can be processed by the processing circuitry  50  in FIG. 3 as playback signals. 
     From FIG. 13 it can be seen that the second AP pinned layer  222  exerts a ferromagnetic coupling field H F    250  on the free layer structure  202 , which is perpendicular to and toward the ABS, and the third AP pinned layer  232  exerts a ferromagnetic coupling field H F    252 , which is also perpendicular to and toward the ABS. Accordingly, the ferromagnetic coupling fields  250  and  252  are additive and tend to rotate the magnetic moment  208  of the free layer downwardly which affects the bias point of the free layer. The ferromagnetic coupling fields  250  and  252  may be completely counterbalanced by a net demagnetization field between the first and second AP pinned structures  204  and  206  exerted on the free layer structure  202  and/or by net sense current fields exerted on the free layer structure by the metallic layers on each side of the free layer structure. In the embodiment shown in FIG. 12 the net demagnetization fields of the first and second AP pinned layer structures  204  and  206  are equal so as to completely counterbalance one another. Accordingly, in this embodiment the sense current fields due to the sense current I s  is employed for counterbalancing the ferromagnetic coupling fields  250  and  252 . It can be seen from FIG. 12 that the first AP pinned structure  204  has 5 Å thick net of ferromagnetic material that produces a net demagnetization field that is perpendicular to and away from the ABS and the second AP pinned layer structure  206  has 5 Å thick net ferromagnetic material which produces a net demagnetization field which is perpendicular to and toward the ABS. Accordingly, the net demagnetization field of each of the first and second AP pinned layer structures  204  and  206  are equal and completely counterbalance each other. 
     As seen in FIG. 12, the sense current I s  causes sense current fields (not shown) from the conductive layers below the free layer structure  202  to be exerted in the free layer structure in a direction perpendicular to and toward the ABS while the sense current fields from the conductive layers above the free layer structure are exerted on the free layer structure perpendicular to and away from the ABS. Since the second AP pinned layer structure  206  is thicker than the first AP pinned layer structure  204  there is a net sense current field on the free layer structure  202  that is perpendicular to and away from the ABS. This is opposite to the directions of the ferromagnetic coupling fields  250  and  252  in FIG. 13 so that counterbalancing can be achieved. Alternatively, the thicknesses of the AP pinned layers in the first and second AP pinned layer structures  204  and  206  can be adjusted so as to provide a net demagnetization field which is in the same direction as the ferromagnetic coupling fields  250  and  252  so that the sense current I s  can be increased. 
     FIGS. 13 and 14 illustrate the manner in which the spin valve sensor  200  can be reset by conducting a voltage pulse through the spin valve sensor from the sense voltage circuit. If the spin valve sensor  200  is in a magnetic disk drive, as shown in FIG. 3, the processing circuitry  50  may be utilized for providing the voltage pulse to the spin valve sensor  200  via the sense voltage circuit which includes the first and second hard bias and lead layers  134  and  136  in FIG.  11 . It is necessary that the voltage pulse raise the temperature of the first and second antiferromagnetic layers  234  and  240  at or near their blocking temperature. In the preferred embodiment the first and second antiferromagnetic layers  234  and  240  are iridium manganese (IrMn) which has a blocking temperature from 250° C. to 260° C. A typical sense voltage Vs is about 0.3 volts. I found that when the voltage pulse is about 1 volt, which is approximately three times the sense voltage Vs, for about 100 ns the temperature of the iridium manganese (IrMn) of the pinning layers  234  and  240  is sufficiently elevated so that the current fields caused by a current pulse through the conductive layers of the spin valve sensor orient the magnetic moment  236  of the first AP pinned layer perpendicular to and away from the ABS and the magnetic moments  242  and  246  of the first and third AP pinned layers of the second AP pinned layer structure to be directed perpendicular to and toward the ABS. When the voltage pulse is terminated and the sensor cools the magnetic spins of the pinning layers  234  and  240  pin the magnetic moments  236  and  242  of the first AP pinned layers  220  and  226  in the directions shown in FIG.  12 . 
     It should be noted that the first AP pinned layer  220  of the first AP pinned layer structure is thicker than the second AP pinned layer  222  which means that the first AP pinned layer  220  is controlling when subjected to the current fields due to the current pulse. In the second AP pinned layer structure  206  the combined thicknesses of the first and third AP pinned layers  226  and  232  is greater than the thickness of the second AP pinned layer  228 . Accordingly, the first and third AP pinned layers  226  and  232  are controlling when the AP pinned layer structure  206  is subjected to the current fields from the voltage pulse. It should be understood that the thicknesses of the AP pinned layers of the first and second AP pinned layer structures  204  and  206  are exemplary and may be varied as desired in order to practice the present invention. It should further be understood that the present spin valve sensor  200  may be reset at the wafer or row level in the construction of multiple magnetic heads by employing a current pulse generator to apply a voltage pulse to the terminals  104  and  106  shown in FIG.  2 . 
     When a sense current I s  is conducted into the paper as shown in FIG. 13 sense current fields H I  from the conductive layers to the left of the first AP pinned layer  226  of the second AP pinned layer structure are exerted on the first AP pinned layer  226  which orients its magnetic moment  242  downwardly and toward the ABS. The sense current fields to the left of the third AP pinned layer  232  of the second AP pinned layer structure also orients the magnetic moment  246  of the third AP pinned layer downwardly and toward the ABS. The magnetic moments  242  and  246  are controlling since their total thickness is greater than the thickness of the second AP pinned layer  228  as discussed hereinabove. Since the first AP pinned layer  220  of the first AP pinned layer structure is controlling the sense current fields H I  from the conductive layers to the right of the first AP pinned layer  220  in FIG. 14 are exerted on the first AP pinned layer  220 . This causes the magnetic moment  236  of the first AP pinned layer to be directed perpendicular to and away from the ABS. Accordingly, a reset voltage pulse causing a current pulse in the same direction as the sense current I s  in FIG. 12, will set the magnetic moments of the AP pinned layers of the first and second AP pinned layer structure  204  and  206  as shown in FIG. 12. I have found that a reset voltage pulse of approximately 1 volt for a period of 100 nanosecond (ns) is sufficient to accomplish the resetting of the magnetic spins of the pinning layers  234  and  240 . A cap layer  248  is located on the second pinning layer  240  for protecting it from subsequent processing steps in the construction of the read head. 
     In the preferred embodiment the blocking temperature of the first and second pinning layers  234  and  248  is below 280° C. Materials with blocking temperatures below 280° C. are iridium manganese (IrMn) with a blocking temperature between 250° C. to 260° C., nickel oxide (NiO) with a blocking temperature between 215° C. to 225° C. and iron manganese (FeMn) with ablocking temperature of approximately 180° C. Of these materials iridium manganese (IrMn) is preferred since its thickness can be between 60 Å to 80 Å and still function as a pinning layer. Further, iridium manganese (IrMn) is not corrosive at its edge which interfaces the ABS. With iridium manganese (IrMn) first and second pinning layers  234  and  240  the read gap between the first and second shield layers  152  and  154  in FIG. 11 is minimized. Accordingly, the linear bit density of the read head is increased for increasing storage capacity of the disk drive shown in FIG.  3 . It should also be noted that the sense current field I s , as directed in FIG. 12, assists in properly pinning the first and second AP pinned layer structures  204  and  206  during operation of the sensor. The sense current I s  causes a sense current field on the first AP pinned layer  220  which is in the same direction as the magnetic moment  236  and the sense current I s  causes a sense current field on each of the first and second AP pinned layers  226  and  232  which is in the same direction as the magnetic moments  242  and  246 . Accordingly, the sense current I s  supplements the pinning of the first and second AP pinned layer structures  204  and  206  by the first and second pinning layers  234  and  240 . 
     Exemplary thicknesses for the layers are 60 Å to 80 Å of iridium manganese (IrMn) for the first pinning layer  234 , 25 Å of cobalt (Co) or cobalt iron (CoFe) for the first AP pinned layer  220 , 8 Å of ruthenium (Ru) for the AP coupling layer  218 , 20 Å of cobalt (Co) or cobalt iron (CoFe) for the second AP pinned layer  222 , 20 Å of copper (Cu) for each of the first and second spacer layers  214  and  216 , 5 Å of cobalt iron (CoFe) for the first and second nanolayers  210  and  212 , 30 Å of nickel iron (NiFe) for the free layer  208 , 20 Å of cobalt iron (CoFe) for the third AP pinned layer  232 , 8 Åof ruthenium (Ru) for the second AP coupling layer  230 , 30 Å of cobalt iron (CoFe) for the second AP pinned layer  228 , 8 Å of ruthenium (Ru) for the first AP coupling layer  224 ,  15 Å o of cobalt (Co) or cobalt iron (CoFe) for the first AP pinned layer  226 , 60 Å to 80 Å of iridium manganese (IrMn) for the second pinning layer  240  and 30 Å of tantalum (Ta) for the cap layer  248 . It should be understood that cobalt (Co) or a cobalt alloy may be substituted for the cobalt iron (CoFe) layers in FIG.  12 . It should further be noted that the cobalt based nanolayers  210  and  212  on each side of the free layer  208  and which are part of the free layer structure  206  are instrumental in promoting the magnetoresistive coefficient dr/R in contrast to the nickel iron (NiFe) free layer  208  interfacing the first and second spacer layers  214  and  216 . 
     Another embodiment of the spin valve sensor  300  is illustrated in FIG.  15 . In this embodiment the order of the first and second AP pinned layer structures  204  and  206  is reversed with the second AP pinned layer structure  206  being located below the free layer structure  202  and the first AP pinned layer structure  204  being located above the free layer structure. This means after construction of the first gap layer  148  in FIG.  11  and the pinning layer  234  in FIG. 15 the second AP pinned layer structure  206  is constructed before constructing the free layer structure  202  and the first AP pinned layer structure  204 . In this embodiment the sense I s  is directed from right to left as shown in FIG.  15 . Further, the current pulse for resetting magnetic spins of the first and second pinning layers  234  and  240  is also from left to right. The magnetic moment  208  of the free layer structure may be oriented from right to left, or from left to right as shown in FIG.  15 . In the embodiment in FIG. 15, when a signal field causes the magnetic moment  208  to be rotated upwardly the resistance of the spin valve sensor will increase and when a signal field causes the magnetic moment  208  to be rotated downwardly the resistance will decrease. 
     Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.