Abstract:
A magnetic head for perpendicular recording on double layer media with suppressed side writing and controlled write width is disclosed. The present invention reduces the problem of side writing and controls the write width of the writing element by providing a writing element with a trailing edge sized dimensionally larger than the leading edge, side shields, and specifically spaced writing gaps placed at various distances between the write element and the side shields, return poles, and the main pole.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/293,278, filed May 23, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention generally relates to magnetic read and write heads for high areal density recording on double layer perpendicular media, and in particular the present invention relates to the writing portion of such head wherein such head has control over the width of the recorded track and skew effect. 
     BACKGROUND OF THE INVENTION 
     As the density of data tracks on magnetic discs continues to increase, increased efficiency of the magnetic read/write head is required. Perpendicular recording, as opposed to the more conventional longitudinal recording, is a form of magnetic recording in which magnetic moments representing bits of data are orientated perpendicularly to the surface of the recording layer of the recording medium. Perpendicular recording may offer advantages over longitudinal recording, such as the ability to achieve higher linear densities, which may be important to extend disc drive technology beyond current data density limitations. 
     To further increase linear density, double layer media may be used in conjunction with perpendicular magnetic heads. Typically the double layer perpendicular media may consist of a high coercivity thin storage layer with perpendicular to-plane anisotropy and a soft magnetic underlayer (keeper) with in-plane anisotropy and relatively high permeability. 
     U.S. Pat. No. 5,181,151 (&#39;151), issued to Masami Yamashita et al, describes a perpendicular recording head having a main pole and a return pole. The space between the main pole and return pole is the write gap. Magnetization transitions on the double layer perpendicular media are recorded by the trailing top edge of the main pole. The recorded transitions reproduce the shape of the main pole projected on the media. The write head of the &#39;151 patent can not control the width of the recorded tracks and hence cannot be used effectively for high track density recording. Further, distribution of the write field across the track width formed by the head as described by Yamashita et al, has a “bell” like shape. The width of the recorded track is defined by the main pole width, write current, media coercivity and space between the head and the soft magnetic underlayer of the media. Due to the shallow field decay profile in cross-track direction, the recorded tracks of the device described in the &#39;151 patent are relatively wide and there is a probability of adjacent track erasure. Thus, there is a need for a magnetic head having controllable width of recorded track and suppressed skew effect. 
     A recording head with controllable track width is described in U.S. Pat. No. 4,656,546. The magnetic head in patent &#39;546 includes a main pole, a return pole, a write gap G between the main pole and return pole, and side shields on either side of the main pole that create side gaps G s . Transitions are recorded at the trailing edge of the main pole that is adjacent to the write gap. The length of the write and side gaps are scaled by the distance D, which is the distance between the head air bearing surface (ABS) and the soft magnetic underlayer of the double layer media. As described in the &#39;546 patent, the distance of write gap G is in the range from D/2 to 2D and the distance of side gaps G s  can be larger than the distance G. The distances of write gap and side gaps that is described in the &#39;546 patent substantially reduce efficiency of the writer and do not support high-track density recording on high coercivity media. The write field in the media of the device described in the &#39;546 patent is believed to barely exceed 6000 Oe and the writer cannot support recording on media with coercivity above 3000 Oe. Hence the head can only be used to record on perpendicular media with a coercivity up to 3000 Oe and a saturation field up to 6000 Oe. That limits the application of &#39;546 high areal density recording due to necessity of higher media coercivity exhibiting high thermal stability. Thus there is a need for a magnetic head that can record on perpendicular media with a saturation field larger than 6000 Oe. The present invention addresses these and other needs and provides advantages that will become apparent to those skilled in the art. 
     SUMMARY OF THE INVENTION 
     The present invention provides a magnetic read/write head design for high-track density recording on double layer perpendicular media with suppressed side writing. The magnetic read/write head of the present invention includes a main pole, a first return pole and magnetic side shields magnetically connected to the first return pole to suppress side writing. The main pole is separated from the first return pole by the write gap in down-track direction and from the magnetic side shield by narrow nonmagnetic gaps in the cross-track direction. To improve the writer efficiency and provide high write field gradient, the length of the write gap should be more than twice the distance between the ABS and the soft magnetic underlayer. Side writing at skew angles is suppressed by providing for the trailing edge of the main pole to be larger than the leading edge of the main pole at the ABS. A side connecting the leading and trailing edge should create an angle that is not less than the maximal skew angles in the drive. 
     In an alternative embodiment, the magnetic read/write head includes a main pole, a first return pole, a second return pole and magnetic side shields magnetically connected to the first and second return poles to suppress side writing. The main pole is separated from the first return pole by the leading write gap in up-track direction. The main pole is also separated from the second return pole by the trailing write gap in down-track direction and the side magnetic shield by narrow nonmagnetic side gaps in the cross-track direction. The leading gap is at least twice the distance of the trailing gap in order to improve writer efficiency and provide high gradient of the write field. 
     These and various other features as well as advantages which characterize the present invention should be apparent to those skilled in the art upon reading the following detailed description and review of the associated drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective front elevational view of a dual stage disc drive actuation system according to the present invention. 
         FIG. 2  is a front view taken from the ABS of a prior typical head for perpendicular recording on double layer media. 
         FIG. 3  is a side cross-sectional view of the head of the type shown in FIG.  2 . 
         FIG. 4  is a side cross-sectional view of a prior typical head for perpendicular recording on double layer media. 
         FIG. 5  is a front view taken from the ABS of head of the type shown in FIG.  4 . 
         FIG. 6  is a graph illustrating that the write field strength in the middle of perpendicular media dependence upon a write gap length. 
         FIG. 7  is a graph showing a distribution of the write field in the middle of a perpendicular media in relation to the width of the cross-track. 
         FIG. 8  is a side cross-sectional view of the magnetic transducer according to the present invention for perpendicular recording with controllable write field gradient, wherein the write element is upstream from the reader element. 
         FIG. 9  is a front view taken from the ABS of the magnetic transducer of the type shown in FIG.  8 . 
         FIG. 10  is a partial sectional perspective view of the magnetic transducer of the type shown in FIG.  8 . 
         FIG. 11  is a magnified partial section perspective view of the magnetic transducer of the type shown in FIG.  10 . 
         FIG. 12  is a side cross-sectional view of an alternative preferred magnetic transducer of the present invention for perpendicular recording with controllable write field gradient, wherein the write element is downstream from the reader element. 
         FIG. 13  is a front view taken from the ABS of the magnetic transducer of the type shown in FIG.  12 . 
         FIG. 14  is a side cross-sectional view of an alternate preferred magnetic transducer of the present invention for perpendicular recording with controllable write field gradient, wherein the write element is downstream from the reader element. 
         FIG. 15  is a front view taken from the ABS of the magnetic transducer of the type shown in FIG.  14 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a perspective view of a disc drive  100  including a dual-stage disc drive actuation system for positioning a head-carrying slider over a track  340  of disc  30 . Disc drive  100  includes voice coil motor  120  arranged to rotate actuator arm  160  on a spindle around axis  140 . Head suspension  180  is connected to actuator arm  160  at head mounting block  200 . A microactuator is attached to head suspension  180  by flexure  220  and carries slider  24 , which in turn carries a transducing head for reading and/or writing data on concentric tracks on disc  30 . Disc  30  rotates around axis  320 , so that windage is encountered by slider  24  to keep it aloft a small distance above the surface of disc  30 . 
       FIGS. 2 and 3  illustrate a conventional head for perpendicular recording that has been described in U.S. Pat. No. 5,181,151 (&#39;151), issued to Masami Yamashita et al. Magnetization transitions on the double layer perpendicular media  300  are recorded by the trailing top edge of trailing main pole  8 . The recorded transitions reproduce the shape of the main pole  8  projected on the media  300 . The write head according to the &#39;151 patent does not provide features to control the width of the recorded tracks and hence cannot be used for high track density recording. Distribution of the write field across the track width has a “bell” like shape. The width of the recorded track is defined by the main pole width, write current, media coercivity and head to the soft magnetic underlayer spacing. Due to the slow field decay profile in cross-track direction, the recorded tracks are relatively wide and there is a probability of adjacent track erasure at high track density recording. 
     A recording head with controllable track width is described in U.S. Pat. No. 4,656,546 (&#39;546) issued to Michael Mallory, is shown in  FIGS. 4 and 5 . Transistions are recorded at the trailing edge of the main pole  27  that is adjacent to the write gap  310 . The main pole  27  is spaced from return pole  210  and side shields  430  and  530 , by write gap  29  and side gaps  190 , respectively. The length of the gaps  29  and  190  is scaled by the distance D between the head ABS and the soft magnetic underlayer  15  of the double layer media  110 . As described in patent &#39;546 in  FIG. 4 , the length G of the write gap  29  is in the range from D/2 to 2D and the length G s  of the side gap  190  can be larger than write gap  29 . 
       FIG. 6  shows the effect of the write gap length on the strength of the write field in the media in regard to the patent described in &#39;546. The gap length G is normalized to the distance D between the main pole  27  and the soft magnetic underlayer  15 . The side gap G s  was assumed to be equal to the write gap. At the conditions claimed in the  FIGS. 4 and 5 , write field in the media barely exceeds 6000 Oe. Hence the head can be used to record on perpendicular media with coercivity up to 3000 Oe and a saturation field up to 6000 Oe. That limits the application of this inventions high areal density recording due to necessity of higher media coercivity exhibiting high thermal stability. 
       FIG. 7  shows the write field distributions in cross-track direction. The calculations were done for head designs according to patents &#39;151 and &#39;546 having identical parameters, and of the head design of the present invention. The width WW of the recorded track is defined for the media with coercivity of 4000 Oe. The head design according to the &#39;151 patent exhibits the highest write field strength but the widest width WW. In contrast, the head design according to the &#39;546 patent has well controlled track width WW, but cannot write on the media due to an insufficient write field. Moreover, both recording heads according to prior art suffer from the skew effect due to rectangular shape of the main pole at the ABS and hence cannot be used for high track density recording. The proposed head exhibits the narrowest track width WW with adequate strength of the write field that is insensitive to skew and can be used for high-track density perpendicular recording on thermally stable high coercivity media. 
     Referring now to  FIGS. 8 ,  9 ,  10 , and  11 , the magnetic read/write head  10  for perpendicular recording on double layer media according to the present invention will be described. The read element includes first return pole  12 , which also serves as a bottom shield, and top shield  16  spaced from each other by the read gap  18  with the GMR element  17  placed in the read gap  18 . The first return pole  12  and top shield  16  are made of soft magnetic material with high permeability and low magnetostriction to provide high stability and high linear resolution of the reading GMR element  17 . 
     The write element is made up of the main pole  11  and first return pole  12  with insulated coil  14  placed in-between and electrically isolated from them. The first return pole  12  is located downstream, relative to the rotation of the double layer media  20 , of main pole  11 . The main pole  11  and first return pole  12  each have a proximal and distal end. The proximal end of the main pole  11  and first return pole  12  are adjacent or proximate the double layer perpendicular media  20 . The main pole  11  and first return pole  12  are magnetically connected to each other on a portion of their distal ends by means of magnetic stud  41 , which collectively form the magnetic core. The magnetic stud  41  is enclosed by electrical coils  14 , which wrap around magnetic stud  41 . At the ABS, the main pole  11  and first return pole  12  are spaced from each other by narrow nonmagnetic write gap  13 . To improve the writer efficiency the main pole  11  has a main pole extension  15  made of soft magnetic material with high permeability. Transitions are recorded on the double layer perpendicular medium  20  composed of the thin top layer  21 , which is a recordable layer having high coercivity and unidirectional perpendicular anisotropy, and bottom layer  22 , which is a soft magnetic underlayer with in-plane anisotropy having low magnetic reluctance. The distance D between the ABS of the main pole  11  and the bottom layer  22  is approximately 20 to 60 nanometers (nm). Further, distance D is not more than two times shorter than distance G of the nonmagnetic write gap  13 , therefore distance G is not less than twice the distance D. This distance provides both high efficiency of the head  10  and high gradient of the write field in the thin top layer  21  during recording. 
     To suppress side writing, the main pole  11  has a trailing edge  40  adjacent to the write gap  13 , which is sized dimensionally larger than the leading edge. The slope angle on the sides of main pole  11  is not less than the largest skew angle in the drive. The head  10  includes side shields  19 , which lie parallel to the tracks on the recording medium  20 . The side shields  19  are spaced from the main pole  11  by side gap  43 . The distance G s  of the side gap  43  is approximately equal to the distance D. The side shields  19  intercept the fringing flux generated by the main pole  11  and prevent erasing or weakening of previously recorded information on adjacent tracks. The write field distribution in cross track direction for head  10  is shown in  FIG. 7 , which also applies to the heads of embodiment 2 and 3. The head of the present invention exhibits the narrowest track width WW with adequate strength of the write field and can be used for high-track density perpendicular recording. 
     An alternate preferred embodiment of the magnetic read/write head  360  for perpendicular recording according to the present invention is shown in  FIGS. 12 and 13 . In this embodiment the head  360  includes first return pole  32 , which also serves as a top shield, and bottom shield  36  spaced from each other by the read gap  38  with the GMR element  37  placed in the read gap  38 . The first return pole  32  and bottom shield  36  are made of soft magnetic material with high permeability and low magnetostriction to provide high stability and high linear resolution of the reading GMR element  37 . Double layer perpendicular media  20  consists of a thin top layer  21 , which is a recordable layer having high coercivity and unidirectional perpendicular ansistropy, and a bottom layer  22 , which is a soft magnetic underlayer having in-plane anistrophy and low magnetic reluctance. 
     The write element includes main pole  31 , main pole extension  35 , and first return pole  32 . Transitions are recorded at the trailing edge  40  of the main pole  31 . The first return pole  32  serves as the top shield of the read sensor pole and is magnetically connected to the side shields  39 . To improve the writer efficiency the main pole  31  has a main pole extension  35  made of soft magnetic material with high permeability. The first return pole  32  is located upstream, relative to the rotation of the double layer media  20 , of main pole  31 . The main pole  31  and first return pole  32  each have a proximal and distal end. The proximal end of the main pole  31  and first return pole  32  are adjacent or proximate the double layer media  20 . The main pole  31  and first return pole  32  are magnetically connected to each other on a portion of their distal ends by magnetic stud  41 , which collectively form the magnetic core. The magnetic stud  41  is enclosed by electrical coils  34 , which wrap around magnetic stud  41 . To suppress side writing at skew, the main pole  31  has a trailing edge  40 , which is sized dimensionally larger than the leading edge. The slope angle on the sides of main pole  31  is not less than the largest skew angle in the drive. The main pole  31  and first return pole  32  are magnetically connected to each other in rear portions, or distal ends, by means of magnetic stud  41 . The distance D between the ABS of the main pole  31  and the bottom layer  22  is approximately 20 to 60 nm. The distance G of write gap  33  is more than four times the distance D. Further, the distance G s  of the of the side gap  43  is approximately equal to the distance D. 
     Another alternate preferred embodiment of the magnetic read/write head for perpendicular recording according to the present invention is shown in  FIGS. 14 and 15 . The head  50  includes first return pole  42 , which also serves as a top shield, and bottom shield  56  spaced from each other by the read gap  58  with the GMR element  57  placed in the read gap  58 . The first return pole  42  and bottom shield  56  are made of soft magnetic material with high permeability and low magnetostriction to provide high stability and high linear resolution of the reading GMR element  57 . Double layer perpendicular media  20  consists of a thin top layer  21 , which is a recordable layer having high coercivity and unidirectional perpendicular ansistropy, and a bottom layer  22 , which is a soft magnetic material having in-plane anistrophy and low magnetic reluctance. 
     To suppress sensitivity to the stray field in the drive, head  50  has two return poles formed by first return pole  42  and second return pole  52  with main pole  51  placed in-between. The first return pole  42  can also be designated as the leading return pole and second return pole  52  can also be designated as the trailing return pole, due to the motion of the media  20 . The first return pole  42  is located upstream, relative to the rotation of the double layer media  20 , of main pole  51 . The main pole  51  and second return pole  52  each have a proximal and distal end. The proximal end of the main pole  51 , first return pole  42 , and second return pole  52  are adjacent or proximate the double layer media  20 . First return pole  42  and second return pole  52  are magnetically connected to each other on a portion of their distal ends by magnetic stud  41  and by side shields  59  at the ABS. The magnetic stud  41  is enclosed by electrical coils  54 , which wrap around magnetic stud  41 , which collectively form the magnetic core. Main pole  51  has a trailing edge  40  adjacent second return pole  52 , which is sized dimensionally larger than the leading edge of main pole  51 . The head  50  has two write gaps  44  and  53 , leading and trailing, respectively. The distance of leading write gap G l  approximately twice or more the distance of trailing gap G t , and trailing gap G t  is approximately twice or more the distance of D. The side shields  59  are spaced from the main pole  51  by the side gaps  43 . The distance G s  of the side gaps  43  are approximately equal to or more than the distance D. Further, the distance D between the ABS of the main pole  51  and the bottom layer  22  is approximately 20 to 60 nm. 
     It is to be understood that even though numerous characteristics and advantages of various embodiments of the present invention have been set forth in the foregoing description, together with details of the structure and function of various embodiments of the invention, this disclosure is illustrative only, and changes may be made in detail, especially in matters of structure and arrangement of parts within the principles of the present invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.