Abstract:
A thin film electromagnetic head has an inductive transducer with a double-nosed ferromagnetic trailing pole layer. The trailing pole layer has a trailing pole tip disposed adjacent to a media-facing surface, a trailing pole yoke disposed distal to the media-facing surface, and a trailing pole nose disposed between the trailing pole tip and the trailing pole yoke. The media-facing surface extends as a substantially flat surface in all directions from the trailing pole tip. The length of the trailing pole nose may be at least twice as long as the trailing pole tip length. The width of the trailing pole nose can be 10 to 30 times as wide as the trailing pole tip width. An inductive transducer having a double-nosed trailing pole layer provides a higher ratio of on-track to off-track write fields, thereby improving the density with which data can be written to the recording media. Such a double-nosed trailing pole layer can be used in transducers for either longitudinal or perpendicular magnetic recording.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to electromagnetic transducers, which may for example be employed in thin film inductive write heads of the type formed on the trailing ends of air bearing sliders used in magnetic recording disk drives. 
     An inductive transducer used for writing and/or reading magnetic information on storage media, such as a disk or tape, typically includes electrically conductive coil windings that encircle a magnetic core. The magnetic core has leading and trailing pole layers. The pole layers have pole tip portions adjacent to the recording media. The magnetic core is interrupted by a submicron nonmagnetic gap disposed between the pole tip portions to divert magnetic flux to the media during writing. To write to the media, electric current is flowed through the coil windings, which produces magnetic flux in the core encircling the coil windings, the magnetic flux fringing across the nonmagnetic gap adjacent to the media so as to write bits of magnetic field information in tracks on the recording media. 
     The leading pole layer is typically substantially flat, whereas the trailing pole layer can be curved in order to cover coil windings and insulation disposed between the pole layers. Alternatively, the trailing pole layer can be flat if a pedestal adjacent to the recording media is magnetically coupled to either the leading or the trailing pole layer. In that case, the submicron nonmagnetic gap is located between the pedestal and the pole layer to which it is not magnetically coupled. 
     The width of the pole tip portion, which corresponds to the track width, may be decreased to allow more tracks to be written on the recording media. As track width is decreased, however, it becomes more difficult to transmit high-intensity magnetic flux through the pole tip portion. A standard technique for increasing the strength of the magnetic field at the pole tip surface has been to increase the magnetic moment of the material near both the pole tip surface and the recording gap. One way to accomplish this is to form a pedestal of material having a high magnetic moment between a pole layer and the recording gap, increasing the magnetic field at the edge of the pole tip surface adjoining the gap. 
     As noted above, the trailing pole layer and/or pedestal may have a flared or tapered width near the region around the pole tip surface in which the sides are parallel. Various geometries of tapered pole layers near the pole tip portions have been used, such as the geometries depicted in  FIGS. 2A–2D . In all of the geometries shown in  FIGS. 2A–2D , the sides  80  immediately adjacent to the pole tip surfaces  82  are parallel. In each of the geometries, after a flare point  84 , the width of the pole layer increases more or less at a steady rate extending away from the pole tip surface  82 . It is also possible that tapered pole layers may have curved regions adjacent pole tip sides. 
       FIG. 2C  is an attempt to replicate the shape of a pole layer disclosed in U.S. Pat. No. 6,055,137 to Ishiwata et al. Ishiwata et al. teach that when the width of the pole-like distal end portion of the other magnetic pole decreases, the magnetic anisotropy of the other magnetic pole becomes difficult to form, and tends to be formed in an undesirable direction. Ishiwata et al. avoid that undesirable magnetic anisotropy by shaping the pole tip with a focused ion beam (FIB) that ablates parts of a trailing pole tip. The “recessed portions” that remain adjacent the pole tip would disrupt the air-bearing surface, however, as well being difficult to form. Moreover, should the FIB be slightly misdirected and cut into the leading pole tip, the etched corners of the leading pole layer may create funnels for off-track flux. 
     SUMMARY 
     A geometry of a pole layer is disclosed that increases the amount of high magnetic moment material near the pole tip surface while limiting off-track writing produced by such material. Such geometry may increase a magnetic flux to be transmitted through the pole tip surface while avoiding leakage of such magnetic flux onto the recording media from areas of the pole layer other than the pole tip surface. For example, an inductive transducer is disclosed that has a double-nosed ferromagnetic trailing pole layer disposed adjacent to electrically conductive coil sections, which are also disposed adjacent to a leading pole layer. The trailing pole layer has a trailing pole tip disposed adjacent to a media-facing surface, a trailing pole yoke disposed distal to the media-facing surface, and a trailing pole nose disposed between the trailing pole tip and the trailing pole yoke. This summary merely lists a few aspects of the disclosure while the invention is defined by the claims appended below. 
    
    
     
       DESCRIPTION OF THE FIGURES 
         FIG. 1A  is a cutaway, opened-up view of a transducer having a double-nosed pole layer with a pole nose between the pole yoke and the pole tip. 
         FIG. 1B  is a cutaway, cross-sectional view of the transducer of  FIG. 1A , showing a pedestal adjacent to and in magnetic contact with a leading pole layer. 
         FIG. 1C  is a cutaway, opened-up view of the transducer as in  FIG. 1A  labeling the dimensions of the pole tip, pole nose and pole yoke. 
         FIG. 1D  is a cutaway, cross-sectional view of the transducer of  FIG. 1A  and  FIG. 1B . 
         FIG. 1E  is a schematic perspective view of the transducer of  FIG. 1A ,  FIG. 1B  and  FIG. 1D . 
         FIGS. 2A–D  (each prior art) depict geometries of pole layers in which, after a flare point, the width of each pole layer increases more or less at a steady rate extending away from the pole tip surface. 
         FIG. 3  is a graph of illustrating write-saturation in Oersted at various currents for on-track and off-track fields and for conventional and double-nosed trailing pole layers. 
         FIG. 4A  illustrates the strength of the magnetic field projected onto the recording media surface from a double-nosed trailing pole layer. 
         FIG. 4B  illustrates the strength of the magnetic field projected onto the recording media surface from a trailing pole layer of conventional geometry. 
         FIG. 5  is a graph comparing the on-track and off-track write fields produced with double-nosed trailing pole layers with trailing pole noses of varying sizes. 
         FIG. 6  is a cutaway, opened-up view of a transducer having a double-nosed pole layer with perpendicular sides, as opposed to the flared sides of  FIG. 1A . 
         FIG. 7  is a cutaway, opened-up view of a transducer having a double-nosed pole layer with rounded sides, as opposed to the perpendicular sides of  FIG. 3 . 
         FIG. 8A  is a cutaway, opened-up view of a transducer having a double-nosed pole layer with a pedestal adjacent to and in magnetic contact with a trailing pole layer. 
         FIG. 8B  is a cutaway, cross-sectional view of the transducer of  FIG. 8A . 
         FIG. 9  is a cutaway, cross-sectional view of an inductive transducer with a pedestal adjoining a trailing pole layer, where the trailing pole layer is curved to cover two layers of coil windings and insulation disposed between the pole layers. 
         FIG. 10  is a cutaway, cross-sectional view of an inductive transducer in which a gap between a leading pole tip surface and a trailing pole tip surface is at least several times larger than the distance between a media-facing surface of the inductive transducer and a recording media. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1B  depicts a first embodiment in accordance with the present invention and shows a cutaway cross-sectional view of a merged inductive and magnetoresistive (MR) transducer  20  of a read/write head. Transducer  20  has been formed in a plurality of adjoining solid layers on a wafer substrate, not shown. A first magnetically soft shield layer  36  has been formed adjacent to the wafer substrate. A first layer of nonmagnetic, electrically insulating material  38  is disposed on the shield layer  36 , adjoining an MR sensor  46 . The MR sensor  46  can be any sensor that utilizes a change in resistance associated with a change in magnetic field to sense that field, which may be measured as a change in current or voltage across the sensor, as the sensor passes over a track on a medium upon which information is stored. 
     A second layer of nonmagnetic, electrically insulating material  40  is disposed between the MR sensor  46  and a second magnetically soft shield layer. The shield layer also serves as a leading pole layer  22  in this example of a merged read/write head. A magnetically soft leading pedestal  50  is magnetically coupled to the leading pole layer  22 . 
     An electrically conductive coil layer  24  has coil sections  26  that are separated from the leading pole layer  22  by additional nonmagnetic, electrically insulating material  54 . The coil sections  26  are substantially parallel in the cross-section shown, and coil layer  24  spirals about a magnetically soft back gap stud, not shown, extending away from a media-facing surface  32  in an area outside that shown in  FIG. 1B . Additional coil layers may optionally be formed, for example, as shown in an embodiment in  FIG. 9 . 
     A flat trailing pole layer  28  is disposed atop the insulating material  54 . The magnetically soft trailing pole layer  28  is composed of high magnetic moment material. The trailing pole layer  28  is coupled to a back gap stud, not shown, so that leading pedestal  50 , leading pole layer  22 , the back gap stud and trailing pole layer  28  form a magnetic loop substantially encircling and electrically isolated from coil sections  26 . The trailing pole layer  28  and the leading pedestal  50  have substantially planar surfaces  34  and  48  adjacent to the recording media. The pole tip surface  48  on leading pedestal  50  is separated from the trailing pole tip surface  34  by a submicron nonferromagnetic gap layer  52 . A protective coating layer  42  forms a trailing end  44  of the body. In this design, the media-facing surface  32  lies on a second, thin protective coating layer  30  that protects the MR sensor  46  from damage and corrosion. In another embodiment the pole tip surface  34  may form part of the media-facing surface  32 . 
     The media-facing surface  32  is in close proximity to a relatively moving medium, not shown, such as a spinning disk. The medium moves in a direction indicated by the arrow pointing towards “y”, so that a leading end of the body encounters a portion of the moving media before the trailing end encounters that media portion. 
       FIG. 1A  is a cutaway, opened-up view of the transducer  20  from above, showing a double-nosed geometry of the trailing pole layer  28 . Also shown are the leading pedestal  50 , the coil sections  26  depicted with hash marks, and protective coating  30  that forms the media-facing surface  32 . The media-facing surface  32  has a substantially flat face containing the trailing pole tip and extending substantially beyond the trailing pole tip in the z direction. 
     The double-nosed trailing pole layer  28  has three regions: a trailing pole tip  72  disposed adjacent to the media-facing surface  32 , a trailing pole yoke  76  disposed distal to the media-facing surface  32 , and a trailing pole nose  74  disposed between the trailing pole tip and trailing pole yoke. The trailing pole tip  72  has sides  60  that are parallel to each other and perpendicular to the media-facing surface  32 . 
     The trailing pole nose  74  has both parallel sides  66  that are parallel to each other and perpendicular to the media-facing surface  32 , as well as flared sides  64  that widen from the trailing pole tip width (TPTW) to the trailing pole nose width (TPNW). The flared sides  64  diverge from each other in a track width dimension, shown in  FIG. 1A  as the z dimension, with increasing distance from the media-facing surface  32 . To avoid accumulation of particles that could channel magnetic flux between the nose and the leading pole tip, it may be desirable for the media-facing surface to be substantially flat on both sides of the trailing pole tip, at least as far as the width of the nose. The media-facing surface adjacent the trailing pole tip may have a substantially flat face for a width at least as great as the TPNW. 
     The trailing pole yoke  76  also has both parallel sides  70  that are parallel to each other and perpendicular to the media-facing surface  32 , as well as flared sides  68  that widen from the trailing pole nose width (TPNW) to the trailing pole yoke width (TPYW). The flared sides  68  diverge from each other in the z dimension with increasing distance from the media-facing surface  32 . 
       FIG. 1C  labels the dimensions of the trailing pole layer  28 , including the trailing pole tip width (TPTW), the trailing pole tip length (TPTL), the trailing pole nose width (TPNW), the trailing pole nose length (TPNL), a trailing pole yoke width (TPYW), an angle θ 1  between a plane parallel to the media-facing surface and the flared sides  64 , and an angle θ 2  between a plane parallel to the media-facing surface and the flared sides  68 . 
       FIG. 1D  is a cut-away, cross-sectional view from the media-facing surface of the transducer  20 . Both the diverging flared sides  64  of the trailing pole nose  74 , as well as the diverging flared sides  68  of the trailing pole yoke  76 , are depicted with hash marks. 
       FIG. 1E  is a schematic perspective view of the transducer  20 . Also shown are axes x, y and z. The recording media moves past transducer  20  in said y direction. The z axis lies on the media-facing surface, not shown in  FIG. 1E , and along the track-width direction. The y axis is orthogonal to the media-facing surface, is perpendicular to both the z axis and the y axis, and intersects both the z axis and the y axis. The intersection of the x, y and z axes lies on the media-facing surface and is centered over the submicron nonferromagnetic gap  52 . 
     The double-nosed geometry of the trailing pole layer  28  increases the amount of the high magnetic moment material in the pole layer that can be placed near the pole tip surface without increasing off-track writing produced by such material. The double-nosed geometry reduces leakage of magnetic flux onto the recording media from areas of the trailing pole layer other than the pole tip surface. Where a conventional trailing pole layer geometry, such as one of the geometries shown in  FIGS. 2A–E , is employed in a transducer having a pedestal coupled to a leading pole layer, the off-track writing results from magnetic flux leakage to the pedestal from the trailing pole layer. 
     Off-track writing is significantly reduced with the double-nosed geometry of the flat trailing pole layer shown in  FIG. 1  because material from the trailing pole layer has been moved away from the media-facing surface. Using a finite element model (FEA) with a write current of 40 mA, the off-track write field at the edge of the leading pedestal is 2650 Oe using a double-nosed trailing pole layer capable of producing a 9400 Oe write field on a narrow trackwidth of 0.28 μm on longitudinal recording media with coercivity of 6000 Oe. When a conventional pole geometry of the shape shown in  FIG. 2A  was used with a flare angle θ 3  of 15°, the write field on the narrow trackwidth of 0.28 μm is 9600 Oe, i.e., only 2% stronger. With the conventional pole geometry, however, the off-track write field at the edge of the leading pedestal increases to 4365 Oe. Thus, off-track writing is reduced about 35% without significantly reducing on-track writing by using the double-nosed trailing pole layer shown in  FIG. 1 . 
       FIG. 3  is a graph comparing the write fields in Oersted at various currents for on-track and off-track fields achieved by a transducer with a conventional trailing pole layer geometry of the shape shown in  FIG. 2A  and by a double-nosed trailing pole layer. The curves in  FIG. 3  include the results at 40 mA described above. 
     The on-track field in  FIG. 3  is measured from the point: x=−2.5 μm, y=0, z=0. The off-track field is measured at: x=−2.5 μm, y=−4.0, z=−4.0. For both conventional and double-nosed pole layer geometries, at low write currents (below about 15 mA) the pole tips do not saturate, and increasing the write current through the coil sections increases the on-track magnetic field without significantly increasing the off-track magnetic field. Above about 15 mA, however, the on-track magnetic fields for pole layers of both geometries begin to saturate, and increasing the write current produces a smaller proportionate increase in the on-track field, as seen by the flatter curves above 15 mA. 
     The off-track magnetic field for pole layers with conventional geometries does not saturate, and increasing the write current beyond 15 mA results in a more or less linear increase in the off-track magnetic field. The off-track magnetic field for double-nosed pole layers, however, begins to saturate beyond about 15 mA of write current, and increasing the write current produces a smaller proportionate increase in the off-track field 15 mA. 
     The double-nosed pole layer, therefore, permits write currents to be used that may reach levels significantly higher than 15 mA, while at the same time keeping the off-track write field within a desired limit, for example, under 3500 Oe. Using higher write currents can have advantages, such as increasing the speed of writing onto the recording media. The on-track write field can be increased to 50 mA with a double-nosed pole layer, for example, without resulting in an off-track write field of more than 3000 Oe. The off-track write field with a conventional pole layer at the same write current would be 5000 Oe. 
     The dimensions of the double-nosed trailing pole layer that were used for the aforementioned modeling were: trailing pole tip width (TPTW) 0.28 μm; trailing pole tip length (TPTL) 0.5 μm; trailing pole nose width (TPNW) 2.0 μm; trailing pole nose length (TPNL) 3.0 μm; trailing pole yoke width (TPYW) 20 μm; and trailing pole yoke length of about 40 μm. The angle θ 1  by which the flared sides  64  diverge away from parallel to the media-facing surface was about 35°, as was the angle θ 2  by which the flared sides  68  diverge away from parallel to the media-facing surface. The conventional pole layer used in the modeling also had a flare angle of 35°, as illustrated by angle θ 3  in  FIG. 2A . 
       FIG. 4A  illustrates the strength of the off-track magnetic field surrounding the leading pedestal obtained from the aforementioned modeling for a double-nosed trailing pole layer  403 . As in  FIG. 1D , the view in  FIG. 4A  is from the x dimension. The 2650 Oe off-track write field at 40 mA appears at locations  404  on an upper edge  401  of the leading pedestal  402  that are at about 0.4 μm and −0.4 μm in the z dimension. 
       FIG. 4B  illustrates the strength of the off-track magnetic field surrounding the leading pedestal  402  obtained from the aforementioned modeling using a conventional trailing pole layer  405  with the geometry of the shape shown in  FIG. 2A . The larger 4365 Oe off-track write field appears at locations  406  on an upper edge  401  of the leading pedestal  402  that are at about 0.4 μm and −0.4 μm in the z dimension. 
       FIG. 5  is a graph comparing the on-track and off-track write fields at various write currents produced with double-nosed trailing pole layers having trailing pole noses with varying cross-sectional areas. The trailing pole layers are made of material having a magnetic moment of 5 Tesla. For a trailing pole layer with a trailing pole nose width of 1 μm, the maximum difference between on-track and off-track write fields can be achieved with a trailing pole nose having an area in a range between about 1 μm 2  and 5 μm 2 . 
     For increasing write currents, the area of the trailing pole nose that yields the maximum difference between on-track and off-track write fields increases. In  FIG. 5 , the on-track and off-track write fields are compared at write currents of 20–60 mA. For a write current of 20 mA, the maximum difference between on-track and off-track fields is achieved with a trailing pole nose having an area between 1 μm 2  and 2 μm 2 . For a write current of 50 mA, the maximum difference between on-track and off-track fields is achieved with a trailing pole nose having an area between 2.5 μm 2  and 3.5 μm 2 . 
     In addition to the difference in on-track and off-track write fields,  FIG. 5  also shows the on-track write fields at the indicated write currents. In order to improve the density with which data can be written to a recording media, it is not generally sufficient to maximize the difference between the on-track and off-track fields if, in doing so, the on-track write field is reduced below a desired level. For example, if an on-track write field of at least 9800 Oe is desired using a write current of 40 mA, then the trailing pole nose geometry that yields the largest difference between on-track and off-track fields should not be used because that geometry reduces the on-track write field below 9800 Oe. 
       FIG. 6  is a cutaway, opened-up view from above of transducer  86  in another embodiment.  FIG. 6  shows the double-nosed geometry of a trailing pole layer  87 , having a trailing pole nose  88  with sides  89  that are not flared, but rather parallel to media-facing surface  90 . Sides  91  are also parallel to the media-facing surface  90  and widen from the trailing pole nose width (TPNW) to the trailing pole yoke width (TPYW). Also shown is leading pedestal  92  below trailing pole layer  87 . 
       FIG. 7  is a cutaway, opened-up view from above of transducer  93  in another embodiment.  FIG. 7  shows the double-nosed geometry of a trailing pole layer  94 , having a trailing pole nose  95  with convex rounded sides  96 . The area of trailing pole nose  95  is at least 75% of the area calculated by multiplying the trailing pole nose length (TPNL) by the trailing pole nose width (TPNW). Planar flared sides  97  diverge from each other in the z dimension with increasing distance from the media-facing surface  98  and widen from the trailing pole nose width (TPNW) to the trailing pole yoke width (TPYW). 
       FIG. 8A  depicts yet another embodiment of a merged inductive and magnetoresistive (MR) transducer  100  having a double-nosed trailing pole layer. This embodiment includes a magnetically soft trailing pedestal  126  that is magnetically coupled to a trailing pole layer  102 . Two portions of a trailing pedestal  126  are represented by cross-hatching and diamond-hatching. The diamond-hatching represents the portion of the trailing pedestal  126  that lies below trailing pole layer  102 . In this embodiment, a trailing pole nose  132  is formed by the trailing pedestal  126  and not by the trailing pole layer  102 . The structure in this embodiment enables the trailing pole nose  132  to be made of material with different magnetic moment than that of the trailing pole yoke, which is substantially formed by the trailing pole layer  102 . Also shown are leading pole layer  116  (represented by square-hatching), coil sections  104  and media-facing surface  108 . 
       FIG. 8B  is a cutaway, cross-sectional view of the transducer  100  of  FIG. 8A . As with transducer  20  shown in  FIG. 1B , transducer  100  also has a magnetically soft shield layer  110 , electrically insulating material  112  and  114 , an MR sensor  122 , leading pole layer  116 , and a coil layer  118  with coil sections  104  that are separated from the leading pole layer  116  by electrically insulating material  128 . 
     Trailing pole layer  102  is disposed atop the insulating material  128 . Trailing pole layer  102  is flat and does not extend all the way to media-facing surface  108 . Magnetically soft trailing pedestal  126  extends to a coating layer  106  that forms the media-facing surface  108 , and the trailing pedestal is magnetically coupled to trailing pole layer  102 . Trailing pedestal  126  and leading pole layer  116  are separated by a submicron gap layer  124 . Another protective coating layer  120  forms a trailing end  130  of the transducer  100 . 
     A double-nosed trailing pole layer can also be formed using a trailing pedestal and a curved trailing pole layer. A curved trailing pole layer might be employed, for example, to cover multiple coil layers. 
       FIG. 9  shows a cutaway, cross-sectional view of another embodiment, wherein transducer  140  has two electrically conductive coil layers  158 A and  158 B, which have coil sections  144  that are separated from a trailing pole layer  142  by electrically insulating material  168 . Trailing pole layer  142  is curved to cover the two coil layers  158 A and  158 B and the insulating material  168 . Trailing pole layer  142  does not extend all the way to a protective coating  146  that forms a media-facing surface  148 . 
     As with transducer  100  in  FIG. 8 , transducer  140  has a trailing pole nose that is formed by a trailing pedestal  166  and not by the trailing pole layer  142 . Trailing pedestal  166  extends to coating layer  146  and is magnetically coupled to trailing pole layer  142 . 
     Also shown in  FIG. 9  are a shield layer  150 , electrically insulating material  152  and  154 , an MR sensor  162 , a leading pole layer  156 , a submicron gap layer  164  formed with part of insulating material  168 , and a protective coating layer  160  that forms a trailing end  170  of the transducer  140 . 
     The first embodiment shown in  FIG. 1B  has a trailing pole layer  28  that is not comprised of sublayers. Other embodiments are possible, however, wherein a trailing pole structure is comprised of more than one layer. Each layer of the trailing pole structure can be composed of material having a different magnetic moment. 
     A double-nosed trailing pole layer can also be used in a perpendicular recording configuration, such as transducer  180  in  FIG. 10 . The embodiments depicted in  FIGS. 1 ,  6 ,  7  and  8  produce longitudinal magnetic recording fields that are parallel to the recording media at the point at which information is written onto the recording media. The embodiment shown in  FIG. 10 , on the other hand, produces a perpendicular recording field. A gap distance  182  between a leading pole layer  184  and a trailing pole layer  186  is considerably wider than the submicron gap layers in  FIGS. 1B and 8B , so that the magnetic flux  188  of the recording field is perpendicular to the recording media  190  at the point adjacent to the trailing edge  192  of the trailing pole layer  186  at which information is written onto the recording media. The ratio of the on-track write field to the off-track write field produced by transducer  180  can be increased by employing the double-nosed pole layer geometry to trailing pole layer  186 . 
     Transducer  180  in  FIG. 10  has a generally U-shaped ferromagnetic core  194  that includes the relatively large leading pole layer  184  through which magnetic flux is returned, the smaller trailing pole layer  186  through which the magnetic flux emanates that writes on the recording media  190 , and a magnetic stud  196  that connects the pole layers  184  and  186 . A conductive coil  198 , including three layers in this embodiment, winds around the magnetic stud  196 . An MR sensor  200  is disposed adjacent a media-facing surface  202  between a magnetically soft shield layer  204  and the trailing pole layer  186 . 
     A transducer in accordance with the present disclosure may be formed as taught in U.S. patent application Ser. No. 09/999,694, filed Oct. 24, 2001 by inventors Yingian Chen et al. and incorporated by reference herein. In addition, by precisely aligning the pole layers and the nose with the MR sensor, it is possible to lap the media-facing surface of the pole tips by the precise amount required to achieve a desired proximity between the nose and the media-facing surface. Precise alignment can be achieved by using a field alignment mark on the lowest layer. Masks for subsequently deposited layers are then always aligned to the same field alignment mark on the lowest layer so that misalignment errors are not compounded when each subsequent layer contains the alignment marks for the layer above. 
     Although the present invention is described in connection with specific embodiments for instructional purposes, the present invention is not limited thereto. The terms leading and trailing are relative to one another and are otherwise not limiting. The sides of the trailing pole nose need not be planar surfaces, and there need be no parallel sides of the trailing pole nose, in order to place the critical amount of trailing pole layer material that is required for the desired on-track write field sufficiently far from the media-facing surface to reduce substantially the off-track write field. Accordingly, various modifications, adaptations and combinations of various features of the described embodiments can be practiced without departing from the scope of the invention as set forth in the following claims.