Abstract:
The present invention provides a modified perpendicular magnetic recording head which generates a relatively small magnetic field in a radial direction through the soft underlayer of a magnetic recording disk in order to reduce unwanted noise from the underlayer. The radial magnetic field is sufficiently strong to effectively drive the magnetic domains out of the soft underlayer underneath the head.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/175,859 filed Jan. 12, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to perpendicular magnetic recording heads, and more particularly relates to a recording head including a radial magnetic field generator which reduces unwanted noise from the soft magnetic underlayer of the recording disk. 
     BACKGROUND INFORMATION 
     Perpendicular magnetic recording systems have been developed for use in computer hard disk drives. A preferred approach to perpendicular magnetic recording requires the use of a magnetically soft underlayer media which provides a flux path from the trailing pole to the leading pole of the writer. The soft underlayer helps with sharp field gradients and also provides strong fields which enable writing on high coercivity media. The soft underlayer is also required during the read operation. During the read back process, the soft underlayer produces the image of magnetic charge, effectively increasing the magnetic flux coming from the media. This provides a higher signal-to-noise ratio. The magnetic anisotropy (H k ) of the soft underlayer can be tailored, typically around 50-100 Oe. This means that a field of approximately 50-100 Oe needs to be applied for the soft underlayer to saturate in the circumferential direction along the length of the recording track. The H k  of the hard magnetic recording layer is typically about 5,000-20,000 Oe. 
     One of the challenges of implementing perpendicular recording is to resolve the problem of soft underlayer noise. The noise is caused by domain wall motion or fringing fields generated by magnetic domains in the soft underlayer that can be sensed by the reader. For the write process to be efficient, high moment materials, e.g., B s &gt;20 kG, may be used for the soft underlayer. If the domain distribution of such materials is not carefully controlled, very large fringing fields can introduce substantial amounts of noise in the read element. Not only can the reader sense the steady-state distribution of magnetization in the soft underlayer, but it can also affect the distribution of magnetization in the soft underlayer, thus generating time-dependent noise. Both types of noise should be minimized. 
     The present invention has been developed in view of the foregoing. 
     SUMMARY OF THE INVENTION 
     The present invention provides a modified perpendicular magnetic recording head which generates a relatively small magnetic field in a radial direction through the soft underlayer of a magnetic recording disk. The radial magnetic field is typically on the order of from about 5 to about 30 Oe, enough to effectively drive the magnetic domains out of the soft underlayer underneath the head. The radial magnetic field is preferably generated in the soft underlayer of the media during the read operation, and may also be generated during the write operation. 
     An aspect of the present invention is to provide a perpendicular magnetic recording head including at least one magnetic recording element, and means for generating a magnetic field which reduces soft magnetic underlayer noise during operation of the magnetic recording element. 
     Another aspect of the present invention is to provide a perpendicular magnetic recording head including at least one magnetic recording element, and a radial magnetic field generator having arms extending along opposing sides of the recording head and spaced apart from the at least one magnetic recording element. 
     A further aspect of the present invention is to provide a perpendicular magnetic recording system comprising a perpendicular magnetic recording disk and a perpendicular magnetic recording head. The disk includes a hard magnetic recording layer and a soft magnetic underlayer, while the perpendicular magnetic recording head includes at least one magnetic recording element and a radial magnetic field generator. 
     These and other aspects of the present invention will be more apparent from the following description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partially schematic side view of a perpendicular magnetic recording head and recording disk illustrating the magnetic flux path through the soft underlayer of the disk during the recording operation. 
     FIG. 2 is a partially schematic bottom view showing the air bearing surface of a perpendicular magnetic recording head which includes both writing and reading elements. 
     FIG. 3 is a partially schematic bottom view showing the air bearing surface of a perpendicular magnetic recording head including a radial magnetic field generator in accordance with an embodiment of the present invention. 
     FIG. 4 is a partially schematic cross-sectional end view taken through section  4 — 4  of FIG. 3, illustrating the recording disk and perpendicular magnetic recording head including a radial magnetic field generator in accordance with an embodiment of the present invention. 
     FIG. 5 is a top view of a magnetic recording disk, schematically illustrating the direction of the magnetic field generated in the soft magnetic underlayer of the disk along the direction of a recording track during the writing operation, and a radial magnetic field generated in the soft underlayer which reduces noise in accordance with an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a partially schematic side view of a perpendicular magnetic recording head  10 . The recording head  10  includes a trailing main write pole  12  and a return pole  14 . A magnetizing coil  15  surrounds a yoke  17  which connects the write pole  12  and return pole  14 . A perpendicular magnetic recording medium  16  such as a disk is positioned under the recording head  10 . The recording medium  16  travels in the direction of the arrow shown in FIG. 1 during recording. The recording medium  16  includes a substrate  18 , which may be made of any suitable material such as ceramic glass, amorphous glass or NiP plated AlMg. A magnetically soft underlayer  20  is deposited on the substrate  18 . Suitable soft magnetic materials for the underlayer  20  include CoFe and alloys thereof, Fe and alloys thereof, FeAlN, NiFe, CoZrNb and FeTaN, with CoFe and FeAlN being preferred soft materials. A thin exchange decouple layer  21  made of a non-magnetic material such as CoCr, Cr or an oxide is deposited on the soft underlayer  20 . A magnetically hard perpendicular recording layer  22  is deposited on the exchange decouple layer  21 . Suitable hard magnetic materials for the recording layer  22  include multi-layers of Co/Pd or Co/Pt, L 10  phases of CoPt, FePt, CoPd and FePd and hcp Co alloys, with such multi layers and L 10  phases being preferred hard materials. A protective overcoat  24  such as diamond-like carbon may be applied over the recording layer  22 . As shown in FIG. 1, during writing operations, magnetic flux is directed along a path M from the main pole  12  perpendicularly through the recording layer  22 , then in the plane of the soft underlayer  20  back to the return pole  14 . 
     FIG. 2 is a partially schematic bottom view of a read/write perpendicular recording head  28  which may be modified in accordance with the present invention. The perpendicular read/write head  28  includes an air bearing surface (ABS)  30  which may be flush with the ends of the main write pole  12  and return pole  14 . In addition to the write poles  12  and  14 , the perpendicular recording head  28  shown in FIG. 2 includes a reader section comprising a read element  32  positioned between shields  34  and  36 . Alternatively, the pole  14  may be combined with the shield  36 . The read element  32  may be a conventional GMR reader or the like. As shown in FIG. 2, during the writing operation, the magnetic flux path M travels from the main pole  12  to the return pole  14 . 
     FIG. 3 is a partially schematic bottom view of a perpendicular magnetic recording head  40  in accordance with an embodiment of the present invention. The recording head  40  includes perpendicular read/write elements adjacent an air bearing surface  30 , similar to the conventional design shown in FIG.  2 . In addition, the recording head  40  of the present invention includes a transverse or radial magnetic field generator  42  comprising arms  44  and  46  which extend along the sides of the recording head  40  substantially flush with the air bearing surface  30 . A coil  48  is wound around a narrowed portion of the base of the radial magnetic field generator  42 . The arms  44  and  46  of the magnetic field generator  42  may be made of any suitable magnetically permeable material such as NiFe, NiFeCo, FeCoB, FeAlN or the like. The coil  48  may be made of any suitable electrically conductive material such as Cu, CrCu, Au or the like. 
     The coil  48  may have any suitable number of turns, e.g., one, two, three or more. For many designs, one or two coil turns are sufficient when currents on the order of 5 to 10 mA are applied to the coil  48 . As shown in FIG. 3, when the coil  48  is activated, a transverse or radial flux pattern R is generated between the arms  44  and  46 . The radial magnetic flux pattern R is substantially perpendicular to the magnetic flux path M between the write poles  12  and  14 . 
     FIG. 4 is a partially schematic cross-sectional end view of the perpendicular magnetic recording head  40  taken through section  4 — 4  of FIG.  3 . For purposes of clarity, only the main pole  12  and the radial flux generator  42 ,  44  and  46  are shown in FIG.  4 . The perpendicular recording medium  16  is positioned under the recording head  40  and travels in a direction perpendicular to the plane of FIG.  4 . The radial magnetic field R travels through the soft underlayer  20  between the arms  44  and  46  of the magnetic field generator  42 . The distance between the arms  44  and  46  may be from about 2 to about 100 microns, for example, from 5 to about 20 microns. The cross-sectional area of each arm may be from about 2 to about 50 square microns, for example, from about 5 to about 20 square microns. As shown in FIG. 4, the arms  44  and  46  may relatively tall and thin. For example, the widths of the arms  44  and  46  may be about 1 micron, while their heights may be from about 5 to 10 micron. 
     In accordance with the present invention, the distance between each of the arms  44 ,  46  and the read/write components  12 ,  14 ,  34  and  36  is relatively large in comparison with the distance between each of the arms  44 ,  46  and the soft underlayer  20  of the disk  16 . This ensures that the radial magnetic field R will follow the path of smallest reluctance through the soft underlayer  20 . For example, the distance D shown in FIG. 3 between the arm  44  and the main pole  12  is much larger than the distance H shown in FIG. 4 between the arm  44  and the soft underlayer  20 . The ratio of D:H may be from about 5:1 to about 50:1. As a particular example, the distance D may be from about 400 to about 500 nm, while the distance H may be from about 40 to about 50 nm. However, the specific distances may vary depending upon the design of the particular recording head. 
     FIG. 5 is a top view illustrating the soft underlayer  20  of the magnetic recording disk  16 . The magnetic field M generated by the perpendicular recording head travels through the soft magnetic underlayer  20  along the direction of the recording tracks of the disk  16  during writing operations. The radial magnetic field R generated in the soft underlayer in accordance with the present invention may be substantially perpendicular to the magnetic field M. The strength of the radial magnetic field R in the soft underlayer  20  is substantially less than the strength of the recording magnetic field M. For example, the radial magnetic field R may be at least 100 times smaller than the recording field M, or at least 1,000 times smaller. For example, the radial magnetic field R may range from about 5 to about 20 or 30 Oe, while the recording magnetic field M may range from about 5,000 to about 20,000 Oe. The radial field R may be smaller than the H k  of the soft underlayer, which typically has a magnetic anisotropy of 50 to 100 Oe. 
     The head structure of the present invention may be built using conventional read and write head fabrication processes, with the additional formation of a shielded structure to provide the radial magnetic field R. To accomplish this, a conventional head structure may be encapsulated with an insulating material such as Al 2 O 3  after the read/write elements have been deposited, e.g., after the main pole  12  of the writer is deposited. The radial magnetic field generator  42 ,  44  and  46  may then be deposited over the insulating material by techniques such as electroplating or sputtering. Alternatively, the radial magnetic field generator  42 ,  44  and  46  may be built up section-by-section at the same time as the individual read/write layers are deposited by conventional masking techniques. For example, in FIG. 3, the reader shield  34  may initially be deposited on a substrate (not shown) and portions of the arms  44  and  46  may be deposited on the substrate up to the level of the shield  34 . Then the reader  32  may be deposited, followed by deposition of additional layers of the arms  44  and  46  up to the level of the reader  32 . The other layers of the head  40  are subsequently deposited in a similar manner, thereby building up the arms  44 ,  46  and the base of the radial magnetic field generator  42  layer by layer. The coil  48  can be formed as either a standard solenoidal or pancake coil around the base  42 . 
     Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.