Abstract:
A two-dimensional magnetic recording (TDMR) read head with an antiferromagnetic (AFM) layer recessed behind a center shield. The TDMR read head comprises a first read sensor and a center shield over the first read sensor, wherein the center shield has a first thickness at an air-bearing surface (ABS) and a second thickness at a back surface, the first thickness being greater than the second thickness. A ferromagnetic layer is disposed over a portion of the center shield, wherein the ferromagnetic layer is recessed from the ABS. The TDMR read head also includes an antiferromagnetic layer over the ferromagnetic layer and a second read sensor over the antiferromagnetic layer. By recessing the AFM layer away from the ABS, the down-track spacing between read sensors is reduced, thereby improving TDMR read head performance.

Description:
BACKGROUND 
     Two-dimensional magnetic recording (TDMR) is a storage architecture that promises to increase the areal density of next-generation hard disk drive products. The ultimate goal in TDMR is for the channel bits to be roughly the same size as the magnetic media grains; in other words, each grain on the magnetic medium ideally stores one bit. In theory, by storing one bit per grain of the magnetic medium, TDMR can achieve a density of 10 terabits per square inch on conventional magnetic storage media available in 2015. 
     The grains of conventional storage media have nonuniform sizes and shapes, and the bit-size-to-grain-size ratio is lower in a TDMR system than in a conventional magnetic recording system. Thus, reading the information stored by a TDMR system is more challenging than reading information stored by a conventional storage system because the highly irregular grain (and, therefore, bit) boundaries cause noise in the read channel, and the tracks are narrow. A TDMR system can recover the stored bits using two-dimensional signal processing techniques if reasonably high-resolution information is available in the cross-track (i.e., from one track to another) and down-track (i.e., along the track being read) dimensions. To obtain such information, a TDMR system can use an array of two or more read elements to create a two-dimensional array of read-back signals, where one dimension is the cross-track dimension, and the other dimension is the down-track dimension. The read sensors can be aligned in the down-track direction (i.e., over the track being read), or they may be offset so that one or more sensors read data from the desired track, and one or more other sensors sense data in adjacent tracks to account for noise. 
     To provide good TDMR read head performance, it is desirable for the read sensors to be electrically isolated from each other as well as magnetically shielded from each other. A center shield is typically disposed between each pair of read sensors of a TDMR read head to provide the electrical isolation and magnetic shielding. The center shield is typically stabilized using an exchange-biased antiferromagnetic (AFM) layer deposited on the center shield. The thickness of the AFM layer increases the down-track spacing (DTS) between the read sensors and reduces the areal density capability (ADC) of the TDMR read head. Therefore, a challenge in TDMR systems is to reduce the DTS between the sensors in the TDMR read head. 
     One way to reduce the DTS is to eliminate the AFM layer altogether, but the unstabilized center shield may induce noise on one or both of the read sensors it is designed to shield and isolate, thereby reducing the TDMR read head performance. Another approach to reduce the DTS is to stabilize the center shield using patterned AFM tabs on each side of the center shield instead of an AFM layer deposited on the center shield; however, to preserve the permeability of the side shield and ensure narrow magnetic read width (MRW) of the lower read sensor (i.e., the sensor under the center shield), these tabs need to be placed away from the lower read sensor. When the tabs are far enough from the lower read sensor to preserve the permeability of the side shield and to ensure narrow MRW, the exchange-biased AFM tabs may not effectively stabilize the center shield. 
     Therefore, there is an ongoing need for approaches that stabilize the center shield while keeping the DTS between read sensors small. 
     SUMMARY 
     Disclosed herein are novel TDMR read heads with the AFM layer recessed behind the center shield. Also disclosed are hard disk drives comprising such TDMR read heads and methods to manufacture the TDMR read heads. By recessing the AFM layer away from the air-bearing surface (ABS) of the TDMR read head, the DTS between read sensors is reduced, thereby improving TDMR read head performance. 
     In some embodiments, a TDMR read head comprises a first read sensor and a center shield over the first read sensor, wherein the center shield has a first thickness at an air-bearing surface (ABS) and a second thickness at a back surface, the first thickness being greater than the second thickness. In some embodiments, the second thickness is zero. The TDMR read head includes a ferromagnetic layer over a portion of the center shield, wherein the ferromagnetic layer is recessed from the ABS. The TDMR read head also includes an antiferromagnetic layer over the ferromagnetic layer and a second read sensor over the antiferromagnetic layer. 
     In some embodiments, the center shield comprises nickel-iron (NiFe), nickel-iron-molybdenum (NiFeMo), nickel-iron-copper (NiFeCu), nickel-iron-chromium (NiFeCr), or other soft magnetic materials with high magnetic permeability. In some embodiments, the center shield comprises a laminate of at least two materials, such as, for example, NiFe, NiFeMo, NiFeCu, or NiFeCr layers separated from each other by one or more anti-ferromagnetic coupling layers made of a material such as ruthenium (Ru). 
     In some embodiments, the antiferromagnetic layer comprises iridium (Ir), manganese (Mn), iridium-manganese (IrMn), platinum-manganese (PtMn), nickel-manganese (NiMn), iron-manganese (FeMn), palladium-manganese (PdMn), rhodium-manganese (RhMn), or a combination of these. 
     In some embodiments, the ferromagnetic layer comprises nickel (Ni), cobalt (Co), iron (Fe), nickel-iron (NiFe), cobalt-iron (CoFe), nickel-iron-chromium (NiFeCr), nickel-iron-molybdenum (NiFeMo), nickel-iron-copper (NiFeCu) cobalt-zirconium-tantalum (CoZrTa), cobalt-zirconium-niobium (CoZrNb), cobalt-iron-zirconium (CoFeZr), or a combination of these. 
     In some embodiments, the ferromagnetic layer comprises a stitch layer and a nanolayer. In some such embodiments, the stitch layer is made of the same material as the center shield. In some embodiments, the nanolayer comprises, for example, cobalt or cobalt-iron alloys (CoFe). 
     In some embodiments, the TDMR read head includes an optional insulator layer disposed over the antiferromagnetic layer and an exposed portion of the center shield. 
     A first method of fabricating a TDMR read head comprises forming a lower read sensor; forming a center shield over the lower read sensor; removing a portion of the center shield so that the center shield has a first thickness at an air-bearing surface (ABS) and a second thickness at a back surface, the first thickness being greater than the second thickness (the second thickness potentially being zero); forming a ferromagnetic layer over a portion of the center shield, wherein the ferromagnetic layer is recessed from the ABS; forming an antiferromagnetic layer over the ferromagnetic layer; and forming an upper read sensor over the antiferromagnetic layer. In some embodiments, the first method also comprises forming an optional insulator layer over the antiferromagnetic layer and an exposed portion of the center shield. In some embodiments, removing the portion of the center shield comprises applying a photoresistive material, and ion milling to remove the portion of the center shield. 
     In some embodiments, forming the ferromagnetic layer comprises forming a stitch layer and a nanolayer. In some such embodiments, the stitch layer is made of the same material as the center shield. The nanolayer may comprise, for example, cobalt-iron (CoFe) or cobalt. 
     In some embodiments, the center shield comprises nickel-iron (NiFe), nickel-iron-molybdenum (NiFeMo), nickel-iron-copper (NiFeCu), nickel-iron-chromium (NiFeCr), or other soft magnetic materials with high magnetic permeability. In some embodiments, the center shield comprises a laminate of at least two materials, such as, for example, NiFe, NiFeMo, NiFeCu, or NiFeCr layers separated from each other by one or more anti-ferromagnetic coupling layers made of a material such as ruthenium (Ru). 
     In some embodiments, the antiferromagnetic layer comprises iridium (Ir), manganese (Mn), iridium-manganese (IrMn), platinum-manganese (PtMn), nickel-manganese (NiMn), iron-manganese (FeMn), palladium-manganese (PdMn), rhodium-manganese (RhMn), or a combination of these. 
     In some embodiments, the ferromagnetic layer comprises nickel (Ni), cobalt (Co), iron (Fe), nickel-iron (NiFe), cobalt-iron (CoFe), nickel-iron-chromium (NiFeCr), nickel-iron-molybdenum (NiFeMo), cobalt-zirconium-tantalum (CoZrTa), cobalt-zirconium-niobium (CoZrNb), cobalt-iron-zirconium (CoFeZr), or a combination of these. 
     A second method of fabricating a TDMR read head comprises forming a lower read sensor; forming a center shield over the lower read sensor, the center shield made of a first material; forming a ferromagnetic layer over the center shield; forming an antiferromagnetic layer over the ferromagnetic layer; removing a portion of the antiferromagnetic and ferromagnetic layers proximate an air-bearing surface (ABS) of the TDMR read head to expose a portion of the center shield; depositing additional first material over the exposed portion of the center shield so that the center shield has a first thickness at the ABS and a second thickness at a back surface of the TDMR read head, the first thickness being greater than the second thickness; and forming an upper read sensor over the antiferromagnetic layer. 
     In some embodiments, the second method further comprises forming an optional insulator layer over the antiferromagnetic layer and the center shield after depositing the additional first material over the exposed portion of the center shield. 
     In some embodiments, forming the ferromagnetic layer comprises forming a stitch layer and a nanolayer. The stitch layer may be made of the same material as the center shield. The nanolayer may comprise, for example, cobalt-iron (CoFe) or cobalt. 
     In some embodiments, removing the portion of the antiferromagnetic and ferromagnetic layers proximate the ABS of the TDMR read head comprises applying a photoresistive material over the antiferromagnetic layer proximate the back surface, and ion milling to remove the portions of the antiferromagnetic and ferromagnetic layers proximate the ABS. 
     In some embodiments, the first material comprises nickel-iron (NiFe), nickel-iron-molybdenum (NiFeMo), nickel-iron-copper (NiFeCu), nickel-iron-chromium (NiFeCr), or other soft magnetic materials with high magnetic permeability. In some embodiments, the center shield comprises a laminate of at least two materials, such as, for example, NiFe, NiFeMo, NiFeCu, or NiFeCr layers separated from each other by one or more anti-ferromagnetic coupling layers made of a material such as ruthenium (Ru). 
     In some embodiments, the antiferromagnetic layer comprises iridium (Ir), manganese (Mn), iridium-manganese (IrMn), platinum-manganese (PtMn), nickel-manganese (NiMn), iron-manganese (FeMn), palladium-manganese (PdMn), rhodium-manganese (RhMn), or a combination of these. 
     In some embodiments, the ferromagnetic layer comprises nickel (Ni), cobalt (Co), iron (Fe), nickel-iron (NiFe), cobalt-iron (CoFe), nickel-iron-chromium (NiFeCr), nickel-iron-molybdenum (NiFeMo), cobalt-zirconium-tantalum (CoZrTa), cobalt-zirconium-niobium (CoZrNb), cobalt-iron-zirconium (CoFeZr), or a combination of these. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure herein is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which like reference numerals refer to similar elements and in which: 
         FIG. 1  illustrates several components of an exemplary hard disk drive in accordance with some embodiments. 
         FIG. 2  is an ABS view showing an exemplary TDMR read/write head in accordance with some embodiments. 
         FIG. 3  is an ABS view of the layers making up a TDMR read sensor in accordance with some embodiments. 
         FIG. 4  illustrates exemplary layers of a TDMR read sensor in accordance with some embodiments. 
         FIG. 5  is a flowchart of a process to fabricate a TDMR read head in accordance with some embodiments. 
         FIG. 6A  is a throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 5 . 
         FIG. 6B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 6A . 
         FIG. 7A  is another throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 5 . 
         FIG. 7B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 7A . 
         FIG. 8A  is another throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 5 . 
         FIG. 8B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 8A . 
         FIG. 9A  is another throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 5 . 
         FIG. 9B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 9A . 
         FIG. 10A  is another throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 5 . 
         FIG. 10B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 10A . 
         FIG. 11A  is another throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 5 . 
         FIG. 11B  is another throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 5 . 
         FIG. 12A  is another throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 5 . 
         FIG. 12B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 12A . 
         FIG. 13A  is another throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 5 . 
         FIG. 13B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 13A . 
         FIG. 14A  is another throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 5 . 
         FIG. 14B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 14A . 
         FIG. 15  is another throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 5 . 
         FIG. 16  is a flowchart of another process to fabricate a TDMR read head in accordance with some embodiments. 
         FIG. 17A  is a throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 16 . 
         FIG. 17B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 17A . 
         FIG. 18A  is a throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 16 . 
         FIG. 18B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 18A . 
         FIG. 19A  is a throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 16 . 
         FIG. 19B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 19A . 
         FIG. 20A  is a throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 16 . 
         FIG. 20B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 20A . 
         FIG. 21  is a throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 16 . 
         FIG. 22A  is a throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 16 . 
         FIG. 22B  is a top-down view of the incomplete TDMR read head device illustrated in  FIG. 22A . 
         FIG. 23  is a throat-cut view of a portion of an incomplete TDMR read head device being fabricated according to the exemplary process illustrated in  FIG. 16 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is made for the purpose of illustrating the general principles of the present disclosure and is not meant to limit the inventive concepts claimed herein. Furthermore, particular features described herein can be used in combination with other described features in various possible combinations and permutations. 
       FIG. 1  illustrates several components of an exemplary hard disk drive in accordance with some embodiments. A magnetic hard disk drive  500  includes a spindle  515  that supports and rotates a magnetic disk  520 . The spindle  515  is rotated by a spindle motor (not shown) that is controlled by a motor controller (not shown) that may be implemented in electronics of the hard disk drive  500 . A slider  525 , which is supported by a suspension and actuator arm  530 , has a combined read and write magnetic head  540 . In some embodiments, the read/write magnetic head  540  is a TDMR read/write head  541 , one embodiment of which is illustrated in  FIG. 2 . The suspension and actuator arm  530  is rotatably positioned over the magnetic disk  520  by an actuator  535 . The head  540  may include one or more giant magnetoresistance (GMR) sensors, tunneling magnetoresistance (TMR) sensors, or another type of magnetoresistive sensor. The components of the hard disk drive  500  may be mounted on a housing  545 . It is to be understood that although  FIG. 1  illustrates a single disk  520 , a single slider  525 , a single head  540 , and a single suspension and actuator arm  530 , hard disk drive  500  may include a plurality (i.e., more than one) of disks  520 , sliders  525 , heads  540 , and suspension and actuator arms  530 . 
     In operation, the actuator  535  moves the suspension and actuator arm  530  to position the slider  525  so that the magnetic head  540  is in a transducing relationship with the surface of the magnetic disk  520 . When the spindle motor rotates the disk  520 , the slider  525  is supported on a thin cushion of air known as the air bearing that exists between the surface of the disk  520  and an air-bearing surface (ABS) of the head  540 . The head  540  may be used to write information to multiple tracks on the surface of the disk  520  and to read previously-recorded information from the tracks on the surface of the disk  520 . Processing circuitry  510  provides signals representing information to be written to the disk  520  to the head  540  and receives signals representing information read from the disk  520  from the head  540 . Processing circuitry  510  also provides signals to the spindle motor to rotate the magnetic disk  520 , and to the actuator  535  to move the slider  525  to various tracks. 
     To read information from the magnetic disk  520 , the head  540  passes over a region of the disk  520  and detects changes in resistance due to magnetic field variations recorded on the disk  520 , which represent the recorded bits. 
       FIG. 2  is an ABS view (i.e., the view from the surface of the disk  520 ) of an exemplary TDMR read/write head  541  in accordance with some embodiments. The TDMR read/write head  541  is comprised of a series of thin films deposited and lithographically patterned on the trailing surface of slider  525  using thin film head fabrication techniques. The writing portion of the TDMR read/write head  541  includes a magnetic write pole  30  and may also include trailing and/or side shields (not shown). 
     In the embodiment illustrated in  FIG. 2 , the read head portion of the TDMR read/write head  541  is shown as a sensor structure of stacked multiple read sensors  100 A,  100 B for use in a disk drive supporting TDMR. In the illustrated embodiment, both read sensors  100 A,  100 B are aligned with one another (vertically in  FIG. 2 ) so as to read the same data track having a certain track width. Sensors  100 A and  100 B may alternatively be laterally offset from each other to adjust for skew, to read different portions of the same track, or to read separate tracks. As illustrated in  FIG. 2 , the sensors  100 A and  100 B are the same size; alternatively, the sensors  100 A,  100 B may have different widths in the cross-track or down-track directions. The widths of the sensors  100 A,  100 B may be based on the track pitch (i.e., the distance from the center of one track to the center of an adjacent track). Furthermore, although  FIG. 2  illustrates TDMR read/write head  541  as having only two sensors,  100 A and  100 B, the TDMR read/write head  541  may include additional sensors  100  in the down-track direction or in the cross-track direction. These additional sensors  100  may be similar to sensors  100 A and  100 B in composition and size, or they may have different compositions or sizes. Similarly, these additional sensors  100  may be aligned with one or both of sensors  100 A,  100 B, or they may be offset from one of both of sensors  100 A,  100 B. 
     For convenience, the sensor  100 A is referred to herein as the “lower read sensor  100 A,” and the sensor  100 B is referred to as the “upper read sensor  100 B.” It is to be understood that the terminology “upper” and “lower” is merely for convenience, and the examples herein include only two sensors  100  to simplify the description. As explained above, the TDMR read/write head  541  may include additional sensors  100 , and sensors  100 A and  100 B may be in a different relationship than sensors  100 A and  100 B shown in  FIG. 2 . For example, sensors  100  may be located next to each other or in any other configuration, which configuration may include more sensors than  100 A and  100 B. The center shield  125  disclosed herein can be disposed between any two read sensors  100  in a TDMR read/write head  541 . As illustrated in the exemplary embodiment of  FIG. 2 , lower read sensor  100 A is located between two magnetic shields, lower shield  15  and center shield  125 . Upper read sensor  100 B is also located between two magnetic shields, center shield  125  and upper shield  25 . The shields  15 ,  25 , and  125  are formed of magnetically permeable material and are also electrically conductive so that they can function as the electrical leads to the read sensors  100 A and  100 B. The shields prevent or reduce the likelihood that the read sensors  100 A and  100 B read recorded data that neighbors the data being read. Typically, lower shield  15  and upper shield  25  may each be up to several microns thick in the down-track direction, whereas the total thickness of each read sensor  100 A,  100 B in the down-track direction is typically in the range of 20 to 40 nm. 
       FIG. 3  is an ABS view of the layers making up a TDMR read head  10  structure in accordance with some embodiments. The layers shown in  FIG. 3  are not necessarily drawn to scale.  FIG. 3  illustrates a stacked current-perpendicular-to-the-plane (CPP) sensor structure, but the disclosures herein apply as well to other types of sensors, such as, for example, current-in-plane (CIP) sensors. As shown in  FIG. 3 , the lower read sensor  100 A is aligned along the same track width as the upper read sensor  100 B, but, as explained above, the two sensors could be laterally misaligned, for example, to adjust for skew, to read different portions of the same data track, or to read adjacent tracks. Likewise, although the lower read sensor  100 A and upper read sensor  100 B are illustrated in  FIG. 3  as being the same size, as explained above, their sizes may be different in the cross-track and/or down-track directions. The lower read sensor  100 A is over lower shield  15 , which is over the slider substrate (not shown), i.e., the trailing surface of the slider  525 . 
       FIG. 4  shows various layers of the read sensor  100 A in accordance with some embodiments. The layers of the read sensor  100 A are not necessarily drawn to scale. As illustrated in  FIG. 4 , the layers of sensor  100 A include a reference or pinned ferromagnetic layer  51  having a fixed magnetic moment or magnetization direction  56  oriented orthogonal to the ABS (into the page), a free ferromagnetic layer  53  having a magnetic moment or magnetization direction  55  oriented substantially parallel to the ABS but that can rotate in the plane of the free layer  53  in response to transverse external magnetic fields from the disk  520 , and a nonmagnetic spacer layer  52  between the pinned layer  51  and the free layer  53 . The sensor  100 A may be a CPP-GMR sensor, in which case the nonmagnetic spacer layer  52  is made of an electrically conducting material, typically a metal such as Cu or Ag, or AgSn alloy. Alternatively, the sensor  100 A may be a CPP tunneling magnetoresistive (CPP-TMR) sensor, in which case the nonmagnetic spacer layer  52  may be a tunnel barrier formed of an electrically insulating material, such as, for example, titanium dioxide (TiO 2 ), magnesium oxide (MgO), or aluminum oxide (Al 2 O 3 ). The pinned layer  51  may have its magnetization direction pinned substantially orthogonal to the ABS by being exchange-coupled to an antiferromagnetic (AF) layer  50 . The AF layer  50  may be made of a manganese (Mn) alloy, e.g., PtMn, NiMn, FeMn, IrMn, PdMn, PtPdMn, or RhMn. The pinned layer  51  may be a simple pinned or an antiparallel pinned structure. A nonmagnetic capping layer  54 , which may be a single layer or multiple layers of different materials, such as ruthenium (Ru), tantalum (Ta), or titanium (Ti), may optionally be located above the free layer  53  to provide corrosion protection and to adjust the free layer  53  to shield spacing. 
     In the presence of an external magnetic field in the range of interest, i.e., magnetic fields from recorded data on the disk  520 , the magnetization direction  55  of the free layer  53  rotates, whereas the magnetization direction  56  of the pinned layer  51  remains fixed and does not rotate. Thus, when a sense current is applied from the top shield  54  perpendicularly through the sensor  100 A layers, the magnetic fields from the recorded data on the disk cause rotation of the free-layer magnetization  55  relative to the pinned-layer magnetization  56 , which is detectable as a change in electrical resistance. 
     Although the free layer  53  is shown in  FIG. 4  as a single layer, the free layer  53  may include multiple layers, such as, for example, provided by a synthetic antiferromagnetic (SAF) structure. Likewise, although the pinned layer  51  is also shown as a single layer, it may have a multilayer structure. 
     Referring again to  FIG. 3 , side shields  60 A,  60 B, which are made of soft magnetic material, are formed outside of the sensor  100 A near the side edges of the sensor  100 A, particularly near the side edges of free layer  53 . The side shields  60 A,  60 B longitudinally bias the magnetization  55  of the free layer  53 . Seed layers  70 A,  70 B are located below the side shields  60 A,  60 B, and insulating layers  80 A,  80 B are located below the seed layers  70 A,  70 B. The seed layers  70 A,  70 B and side shields  60 A,  60 B are electrically insulated from the side edges of the sensor  100 A by electrically insulating layers  80 A,  80 B, which may be made of aluminum oxide (Al 2 O 3 ), a silicon nitride (Si 3 N 4 ), or another metal oxide such as, for example, a tantalum oxide or a titanium oxide. The side shields  60 A,  60 B are formed of “soft” magnetic material, meaning material that can be easily magnetized and demagnetized at low magnetic fields. The soft magnetic material may be any of the well-known materials used for conventional magnetic shields, such as, for example, an alloy comprising nickel (Ni) and iron (Fe). Alternatively, other soft ferromagnetic materials may be used, such as, for example, NiFeCr, NiFeMo, NiFeCu, CoZrTa, CoZrNb, or CoFeZr alloys. 
     Upper read sensor  100 B is similar in structure and function to lower read sensor  100 A. As mentioned elsewhere, upper read sensor  100 B may be the same size as lower read sensor  100 A, or it may have different dimensions. Like lower read sensor  100 A, upper read sensor  100 B comprises an antiferromagnetic layer, a pinned layer with its magnetization orthogonally pinned to the ABS, a spacer layer, a free layer with its magnetization oriented substantially parallel to the ABS but free to rotate, and (optionally) a nonmagnetic cap layer. The discussion of these layers is provided above in the discussion of lower read sensor  100 A. Like lower read sensor  100 A, upper read sensor  100 B is sandwiched by side shields  61 A,  61 B, seed layers  71 A,  71 B, and insulating layers  81 A,  81 B. The side shields  61 A,  61 B, seed layers  71 A,  71 B, and insulating layers  81 A,  81 B may have the same structure, composition, and function as previously described for lower read sensor  100 A. 
     Center shield  125  is a shared shield between lower read sensor  100 A and upper read sensor  100 B. Center shield  125  electrically isolates sensors  100 A,  100 B from each other and magnetically shields the sensors  100 A,  100 B from each other. As stated above, for a number of reasons, it is desirable to minimize the distance between the upper read sensor  100 B and the lower read sensor  100 A. One reason is to mitigate the effects of head skew, which is a result of the rotary actuator  535  not moving the TDMR read/write head  541  perfectly radially across the tracks of the disk  520 . Near the outside diameter of the disk  520 , the skew angle may be positive, whereas closer to the center of the disk  520 , the skew angle may be negative. Whenever the skew angle is nonzero, the read sensors in a multi-sensor array (e.g., the read sensors  100 A,  100 B illustrated in  FIG. 2  and  FIG. 3 ) may be misaligned relative to the track they are intended to sense (regardless of whether the sensors are intended to sense the same track or different tracks). As a result, the read sensors may not perform as desired at all skew angles. Head skew is most pronounced near the inner and outer diameters of the disk  520  (see  FIG. 1 ). To mitigate the effects of head skew in TDMR, the center shield  125 , and any layers used to stabilize the center shield  125 , should be made as thin as possible without substantially degrading shielding and resolution. 
       FIG. 5  illustrates a process  400  of fabricating a TDMR read head  10  (i.e., a portion of the TDMR read/write head  541 ) having two read sensors separated by a center shield that is stabilized by a recessed AFM layer in accordance with some embodiments.  FIGS. 6A through 15  illustrate the incomplete TDMR read head  10  at various stages of fabrication according to the process  400  of  FIG. 5 . It is to be understood that the layers and dimensions of the various layers of the TDMR read head  10  shown in  FIGS. 6A to 15  are not necessarily to scale. 
     Referring to  FIG. 5 , at  405 , the process  400  begins. At step  410 , a lower shield (e.g., lower shield  15  shown in  FIG. 2  or  FIG. 3 ) is formed on a substrate (e.g., a substrate of slider  525 ). At step  415 , a first read sensor (e.g., the lower read sensor  100 A shown in  FIG. 2  or  FIG. 3 ) is formed on the lower shield between a first side shield and a second side shield (e.g., side shields  60 A and  60 B shown in  FIG. 2  or  FIG. 3 ). The lower shield  15 , lower read sensor  100 A, and side shields  60 A and  60 B can be formed using conventional fabrication techniques and conventional materials, and their sizes and thicknesses can be conventional. 
       FIG. 6A  is a throat cut view of a portion of the incomplete TDMR read head  10  through one of the side shields (side shield  60 A) after the lower read sensor  100 A and the side shields  60 A and  60 B have been fabricated over the lower shield  15  (i.e., after steps  410  and  415  of  FIG. 5 ).  FIG. 6A  identifies the air-bearing surface (ABS)  110  and the back surface  115  of the incomplete TDMR read head  10 .  FIG. 6B  illustrates the top-down view of the incomplete TDMR read head  10  illustrated in  FIG. 6A .  FIG. 6B  shows the lower read sensor  100 A between side shields  60 A and  60 B. 
     Referring again to  FIG. 5 , at step  420 , a center shield (e.g., center shield  125  shown in  FIG. 2  or  FIG. 3 ) is formed over the first read sensor  100 A and the first and second side shields  60 A,  60 B. The center shield  125  may be formed of any suitable material. In some embodiments, the center shield  125  is made of nickel-iron (NiFe), nickel-iron-molybdenum (NiFeMo), nickel-iron-copper (NiFeCu), nickel-iron-chromium (NiFeCr), or other soft magnetic materials with high magnetic permeability. In some embodiments, the center shield  125  has a laminated structure comprising at least two materials, such as, for example, NiFe layers separated from each other by anti-ferromagnetic coupling layers such as ruthenium (Ru). If the center shield  125  is made of NiFe, the center shield  125  may be fabricated by depositing alternating thin layers of nickel and iron. 
       FIG. 7A  is a throat-cut view of a portion of the in-fabrication TDMR read head  10  after step  420  of  FIG. 5 . The center shield  125  may have any suitable thickness but may typically be in the range of 75 Angstroms to 500 Angstroms. A thickness of 180 Angstroms has been found to be advantageous.  FIG. 7B  is the top-down view of the TDMR read head  10  corresponding to  FIG. 7A . 
     Referring again to  FIG. 5 , at step  425 , a portion of the center shield  125  is removed so that a remaining portion of the center shield  125  has a first thickness at the ABS that is greater than a second thickness at the back surface of the read head  10 . The removal of the portion of the center shield  125  can be accomplished using well-known, conventional techniques, such as, for example, applying photoresistive material or a hard mask and ion-milling or etching to remove the portion of the center shield  125 . 
       FIG. 8A  is a throat-cut view of the incomplete TDMR read head  10  before the portion of the center shield  125  has been removed in step  425 . As shown in the embodiment illustrated in  FIG. 8A , photoresistive material  130  has been deposited over an area of the center shield  125  near the ABS  110  of the TDMR read head  10 . The photoresistive material  130  can be any conventional material that protects the portion of the center shield  125  near the ABS  110  while another portion of the center shield  125  closer to the back surface  115  is being removed (e.g., by etching or ion milling). A hard mask or other well-known techniques to lithographically define a region of the TDMR read head  10  to be protected during a subsequent fabrication step could be used instead of the exemplary photoresistive material  130  shown in  FIG. 8A . 
       FIG. 8B  is a top-down view of the incomplete TDMR read head  10  after the photoresistive material  130  has been deposited as illustrated in  FIG. 8A . 
       FIG. 9A  is a throat-cut view of the incomplete TDMR read head  10  after the portion of the center shield  125  closer to the back surface  115  has been removed. As shown in  FIG. 9A , after the removal, the center shield  125  has a first thickness  155  at the ABS  110  that is greater than a second thickness  160  at the back surface  115 . The first thickness  155  may be, for example, 75 Angstroms to 500 Angstroms, whereas the second thickness  160  may be, for example, from zero to 450 Angstroms. A center shield  125  having a first thickness  155  of around 200 Angstroms and a second thickness  160  of around 100 Angstroms has been found to be advantageous. 
       FIG. 9B  is a top-down view of the incomplete TDMR read head  10  after the portion of the center shield  125  has been removed in step  425  of  FIG. 5 . 
     Referring again to  FIG. 5 , at step  430 , a ferromagnetic layer  165  is formed over the remaining portion of the center shield  125 .  FIG. 10A  is a throat-cut view of the incomplete TDMR read head  10  after the ferromagnetic layer  165  has been formed, and  FIG. 10B  is the corresponding top-down view. Because the ferromagnetic layer  165  is deposited while the photoresistive material  130  (or other suitable protective mechanism) is in place, the ferromagnetic layer  165  is recessed from the ABS  110 , as shown in  FIG. 10A . The ferromagnetic layer  165  may be made of any suitable material, such as, for example, nickel (Ni), cobalt (Co), iron (Fe), nickel-iron (NiFe), cobalt-iron (CoFe), nickel-iron-chromium (NiFeCr), nickel-iron-molybdenum (NiFeMo), cobalt-zirconium-tantalum (CoZrTa), cobalt-zirconium-niobium (CoZrNb), cobalt-iron-zirconium (CoFeZr), or a combination of these. The ferromagnetic layer  165  may have any suitable thickness, for example, between 10 and 50 Angstroms. A thickness of around 20 Angstroms has been found to be advantageous. 
     In some embodiments, the ferromagnetic layer  165  includes a stitch layer  135  and a nanolayer  140 . In other embodiments, the ferromagnetic layer  165  does not include a stitch layer  135  or a nanolayer  140 .  FIGS. 11A and 11B  illustrate an embodiment in which the ferromagnetic layer  165  includes a stitch layer  135  and a nanolayer  140 .  FIG. 11A  is a throat-cut view of an embodiment of the incomplete TDMR read head  10  after a stitch layer  135  has been formed over a portion the center shield  125 . As shown in  FIG. 11A , the stitch layer  135  is recessed from the ABS  110  of the TDMR read head  10 . The stitch layer  135  may be made of any suitable material, such as, for example, nickel (Ni), cobalt (Co), iron (Fe), nickel-iron (NiFe), cobalt-iron (CoFe), nickel-iron-chromium (NiFeCr), nickel-iron-molybdenum (NiFeMo), nickel-iron-copper (NiFeCu), cobalt-zirconium-tantalum (CoZrTa), cobalt-zirconium-niobium (CoZrNb), cobalt-iron-zirconium (CoFeZr), or a combination of these. In some embodiments, the stitch layer  135  is made of the same material as the center shield  125 . The stitch layer  135  may have any suitable thickness, such as, for example, between 10 and 50 Angstroms. A thickness of around 20 Angstroms has been found to be advantageous. 
       FIG. 11B  is a throat-cut view of an incomplete TDMR read head  10  after a nanolayer  140  has been formed over the stitch layer  135 . The nanolayer  140  may be made of any suitable material, such as, for example, nickel (Ni), cobalt (Co), iron (Fe), nickel-iron (NiFe), cobalt-iron (CoFe), nickel-iron-chromium (NiFeCr), nickel-iron-molybdenum (NiFeMo), nickel-iron-copper (NiFeCu), cobalt-zirconium-tantalum (CoZrTa), cobalt-zirconium-niobium (CoZrNb), cobalt-iron-zirconium (CoFeZr), or a combination of these. In some embodiments, the nanolayer  140  promotes exchange biasing of the antiferromagnetic layer  145  that is subsequently deposited as described below. The nanolayer  140  may have any suitable thickness, such as, for example, between 3 and 10 Angstroms. A thickness of around 5 Angstroms has been found to be advantageous. 
     Referring again to  FIG. 5 , at step  435 , an antiferromagnetic layer  145  is formed over the ferromagnetic layer  165 . The antiferromagnetic layer  145  may be made of any suitable material, such as, for example, iridium and manganese. For example, the antiferromagnetic layer  145  may be an alloy such as IrMn (where Mn is between about 70 and 85 atomic percent), or any other antiferromagnetic material, such as, for example, PtMn, NiMn, FeMn, PdMn, PtPdMn, or RhMn. The antiferromagnetic layer  145  may have any suitable thickness, for example, between 60 and 100 Angstroms. A thickness of around 80 Angstroms has been found to be advantageous. 
       FIG. 12A  is a throat-cut view of the incomplete TDMR read head  10  after the antiferromagnetic layer  145  has been formed over the ferromagnetic layer  165 , and  FIG. 12B  is the corresponding top-down view. 
     In some embodiments, any protective material (e.g., photoresistive material  130 ) deposited to facilitate the removal of the portion of the center shield  125  and to facilitate the formation of an antiferromagnetic layer  145  that is recessed from the ABS  110  is removed after the antiferromagnetic layer  145  has been formed.  FIG. 13A  is a throat-cut view of the incomplete TDMR read head  10  after the photoresistive material  130  has been removed from the TDMR read head  10 , and  FIG. 13B  is the corresponding top-down view. 
     Referring again to  FIG. 5 , at step  440 , an insulator layer  150  is optionally formed over the antiferromagnetic layer  145  and an exposed portion of the center shield  125  that was previously protected by the photoresistive material  130 .  FIG. 14A  is a throat-cut view of the incomplete TDMR read head  10  after the optional insulator layer  150  has been formed over the antiferromagnetic layer  145  and the exposed portion of the center shield  125 , and  FIG. 14B  is the corresponding top-down view. If included, the insulator layer  150  may be made of a material having a low dielectric constant (e.g., a material having a dielectric constant of less than eight), such as silicon oxide (SiO) or silicon oxycarbide (SiOC). If included, the insulator layer  150  may have any suitable thickness, for example, between 30 and 100 Angstroms. A thickness of 40 Angstroms has been found to be advantageous. 
     Referring again to  FIG. 5 , at step  445 , the remainder of the TDMR read head  10 , including a second read sensor (e.g., upper read sensor  100 B) and any associated shields, insulating layers, and/or seed layers (as shown, for example, in  FIG. 3 ), is formed. At  450 , the process ends. 
     As explained above, although  FIG. 5  contemplates a TDMR read head  10  having two read sensors, it is to be understood that the process  400  to fabricate a recessed antiferromagnetic layer  145  to stabilize a center shield  125  can be used to fabricate a TDMR read head  10  having more than two read sensors  100 . 
     As explained above, after the portion of the center shield  125  closer to the back surface  115  of the TDMR read head  10  has been removed, the center shield  125  is thicker at the ABS  110  than at the back surface  115 . In some embodiments, a first thickness  155  of the center shield  125  is a nonzero value, and a second thickness  160  of the center shield  125  at the back surface  115  is zero or close to zero.  FIG. 15  is a throat-cut view of an incomplete TDMR read head  10  in which the center shield  125  ends well short of the back surface  115 . In other words, the center shield  125  has been completely removed at the back surface  115  so that the second thickness  160  is zero. In contrast, the first thickness  155  at the ABS  110  is a nonzero value. 
       FIG. 16  is a flowchart of a second process  600  to fabricate a TDMR read head  10  in accordance with some embodiments.  FIGS. 17A through 23  illustrate the incomplete TDMR read head  10  at various stages of fabrication according to the process  600  of  FIG. 16 . The layers and dimensions of the various layers of the TDMR read head  10  shown in  FIGS. 17A to 23  are not necessarily to scale. 
     At  605 , the process begins. At step  610 , a lower shield (e.g., lower shield  15 ) is formed. At step  615 , a first read sensor (e.g., the lower read sensor  100 A) and its associated side shields (e.g., side shields  60 A,  60 B) are formed over the lower shield. Steps  610  and  615  are identical to steps  410  and  415 , respectively, of  FIG. 5  and are not discussed further here.  FIGS. 6A and 6B  illustrate the throat-cut and top-down views of the TDMR read head  10  after completion of steps  610  and  615 . 
     At step  620 , a center shield  125  is formed over the first read sensor and side shields. In some embodiments, step  620  is identical to step  420  of  FIG. 5 . The center shield  125  may be fabricated using any suitable material, such as, for example, nickel-iron (NiFe), nickel-iron-molybdenum (NiFeMo), nickel-iron-copper (NiFeCu), nickel-iron-chromium (NiFeCr), or a combination of these. As explained previously, the center shield may have a laminated structure comprising at least two materials, such as, for example, NiFe layers separated from each other by anti-ferromagnetic coupling layers such as ruthenium (Ru). If the center shield  125  is made of NiFe, the center shield  125  may be fabricated by depositing alternating thin layers of nickel and iron. The center shield  125  may have any suitable thickness but may typically be in the range of 75 Angstroms to 500 Angstroms. A thickness of 180 Angstroms has been found to be advantageous. In some embodiments, the thickness of the center shield  125  formed in step  620  is the desired second thickness  160  of the center shield  125  at the back surface  115  of the TDMR read head  10 .  FIGS. 7A and 7B  illustrate the throat-cut and top-down views of the TDMR read head  10  after completion of step  620 . 
     Referring again to  FIG. 16 , at step  625 , a ferromagnetic layer  165  is formed over the center shield  125 . The ferromagnetic layer  165  may be made of any suitable material, such as, for example, nickel (Ni), cobalt (Co), iron (Fe), nickel-iron (NiFe), cobalt-iron (CoFe), nickel-iron-chromium (NiFeCr), nickel-iron-molybdenum (NiFeMo), nickel-iron-copper (NiFeCu), cobalt-zirconium-tantalum (CoZrTa), cobalt-zirconium-niobium (CoZrNb), cobalt-iron-zirconium (CoFeZr), or a combination of these. The ferromagnetic layer  165  may have any suitable thickness, for example, between 10 and 50 Angstroms. A thickness of around 20 Angstroms has been found to be advantageous. As explained earlier in the context of  FIG. 5 , the ferromagnetic layer  165  can include a stitch layer  135  and a nanolayer  140 . 
       FIG. 17A  is a throat-cut view of a portion of an incomplete TDMR read head device after the ferromagnetic layer  165  has been formed over the center shield  125 , and  FIG. 17B  is the corresponding top-down view. 
     Referring again to  FIG. 16 , at step  630 , an antiferromagnetic layer  145  is formed over the ferromagnetic layer  165 . The antiferromagnetic layer  145  may be made of any suitable material, such as, for example, iridium and manganese. For example, the antiferromagnetic layer  145  may be an alloy such as IrMn (where Mn is between about 70 and 85 atomic percent), or any other antiferromagnetic material, such as, for example, PtMn, NiMn, FeMn, PdMn, PtPdMn, or RhMn. The antiferromagnetic layer  145  may have any suitable thickness, for example, between 60 and 100 Angstroms. A thickness of around 80 Angstroms has been found to be advantageous. 
       FIG. 18A  is a throat-cut view of a portion of an incomplete TDMR read head device  10  after completion of step  630  of  FIG. 16 , and  FIG. 18B  is the corresponding top-down view. 
     Referring again to  FIG. 16 , at step  635 , a portion of the antiferromagnetic layer  145  proximate the ABS  110  and a portion of the ferromagnetic layer  165 , also proximate the ABS  110 , are removed, thereby exposing a portion of the center shield  125 . The portions of the antiferromagnetic layer  145  and the ferromagnetic layer  165  can be removed using well-known, conventional techniques, such as, for example, applying photoresistive material or a hard mask and ion-milling or etching to remove the desired portions of the antiferromagnetic layer  145  and the ferromagnetic layer  165 . 
       FIG. 19A  is a throat-cut view of the incomplete TDMR read head  10  before the portions of the antiferromagnetic layer  145  and the ferromagnetic layer  165  have been removed. As shown in the embodiment illustrated in  FIG. 19A , photoresistive material  130  has been deposited over an area of the antiferromagnetic layer  145  proximate the back surface  115  of the TDMR read head  10 . The photoresistive material  130  can be any conventional material that protects the portion of the TDMR read head  10  near the back surface  115  while material (i.e., the portions of the antiferromagnetic layer  145  and the ferromagnetic layer  165 ) closer to the ABS  110  is being removed. As stated previously, a hard mask or other well-known techniques to lithographically define a region of the TDMR read head  10  to be protected during a subsequent fabrication step could be used instead of the photoresistive material  130  shown in  FIG. 19A .  FIG. 19B  is a top-down view of the incomplete TDMR read head  10  after the photoresistive material  130  has been deposited as illustrated in  FIG. 19A . 
       FIG. 20A  is a throat-cut view of the incomplete TDMR read head  10  after the portions of the antiferromagnetic layer  145  and the ferromagnetic layer  165  proximate the ABS  110  have been removed in step  635  of  FIG. 16  to expose a portion of the center shield  125 , and  FIG. 20B  is the corresponding top-down view. 
     Referring again to  FIG. 16 , at step  640 , additional center shield  125  material is deposited over the exposed portion of the center shield  125 , filling at least a portion of the region previously occupied by the portions of the antiferromagnetic layer  145  and ferromagnetic layer  165  removed in step  635 .  FIG. 21  is a throat-cut view of a portion of the incomplete TDMR read head  10  after additional center shield  125  material has been deposited in step  640  of  FIG. 16 . As illustrated in the embodiment of  FIG. 21 , enough additional center shield  125  material has been deposited to bring the height of the center shield  125  at the ABS  110  to approximately the height of the antiferromagnetic layer  145 . In other embodiments, more or less additional center shield  125  material can be deposited. As shown in  FIG. 21 , the center shield  125  has a first thickness  155  at the ABS  110  and a second thickness  160  at the back surface  115 , where the first thickness  155  is greater than the second thickness  160 . 
       FIG. 22A  is a throat-cut view of a portion of the incomplete TDMR read head  10  after the photoresistive material  130  has been removed after completion of step  640  of  FIG. 16 , and  FIG. 22B  is the corresponding top-down view. 
     Referring again to  FIG. 16 , at step  645 , an optional insulator layer  150  is formed over the antiferromagnetic layer  145  and the exposed portion of the center shield  125 .  FIG. 23  is a throat-cut view of the incomplete TDMR read head  10  after the optional insulator layer  150  has been formed. If included, the insulator layer  150  may be made of a material having a low dielectric constant (e.g., a material having a dielectric constant of less than eight), such as silicon oxide (SiO) or silicon oxycarbide (SiOC). If included, the insulator layer  150  may have any suitable thickness, for example, between 30 and 100 Angstroms. A thickness of 40 Angstroms has been found to be advantageous. 
     Referring again to  FIG. 16 , at step  650 , the remainder of the TDMR read head  10 , including a second read sensor (e.g., upper read sensor  100 B) and any associated shields, insulating layers, and/or seed layers (as shown, for example, in  FIG. 3 ), is formed. At  655 , the process ends. 
     In the foregoing description and in the accompanying drawings, specific terminology has been set forth to provide a thorough understanding of the disclosed embodiments. In some instances, the terminology may imply specific details that are not required to practice the invention. For example, the materials used in a TDMR read head  10  may be different from those described above in various embodiments. Similarly, the processes used to fabricate a TDMR read head  10  may be different from those described above in various embodiments. For example, the lithographic processes may differ from those described above. 
     To avoid obscuring the present disclosure unnecessarily, well-known components (e.g., of a disk drive) or layers (e.g., of TDMR devices or read sensors) are shown in block diagram form and/or are not discussed in detail or, in some cases, at all. Unless otherwise indicated herein, prior-art fabrication processes and known materials may be used for the disclosed TDMR read head  10 . 
     Unless otherwise specifically defined herein, all terms are to be given their broadest possible interpretation, including meanings implied from the specification and drawings and meanings understood by those skilled in the art and/or as defined in dictionaries, treatises, etc. The terms “magnetization,” “direction of magnetization,” “magnetization direction,” and “magnetic moment” are used interchangeably herein. 
     As used in the specification and the appended claims, the singular forms “a,” “an” and “the” do not exclude plural referents unless otherwise specified. The word “or” is to be interpreted as inclusive unless otherwise specified. Thus, the phrase “A or B” is to be interpreted as meaning all of the following: “both A and B,” “A but not B,” and “B but not A.” Any use of “and/or” herein does not mean that the word “or” alone connotes exclusivity. 
     The term “coupled” is used herein to express a direct connection as well as a connection through one or more intervening circuits or structures. To the extent that the terms “include(s),” “having,” “has,” “with,” and variants thereof are used in the detailed description or the claims, such terms are intended to be inclusive in a manner similar to the term “comprising,” i.e., meaning “including but not limited to.” The terms “exemplary” and “embodiment” are used to express examples, not preferences or requirements. 
     The terms “over,” “under,” “between,” and “on” are used herein refer to a relative position of one layer with respect to other layers. For example, one layer disposed “over” or “under” another layer may be directly in contact with the other layer or may have one or more intervening layers. Moreover, one layer disposed “between” two layers may be directly in contact with the two layers or may have one or more intervening layers. In contrast, a first layer “on” a second layer is in contact with that second layer. Additionally, the relative position of one layer with respect to other layers is provided assuming operations are performed relative to a substrate without consideration of the absolute orientation of the substrate. 
     Although the drawings illustrate most layers as being single layers, many of these layers may have multilayer structures, as would be appreciated by a person having ordinary skill in the art. Similarly, the drawings are not necessarily to scale, and the dimensions of the layers and TDMR read head  10  may differ substantially from how they are depicted in the drawings. 
     Although specific embodiments have been disclosed, it will be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the disclosure. For example, features or aspects of any of the embodiments may be applied, at least where practicable, in combination with any other of the embodiments or in place of counterpart features or aspects thereof. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.