Abstract:
A perpendicular magnetic recording head includes a perpendicular writing pole and a longitudinal field generator which rotates the magnetization of the perpendicular recording media prior to writing, thereby facilitating magnetization switching. The longitudinal magnetic field may be provided by a narrowed gap between the trailing write pole and the leading return pole of the head. The gap structure is designed to provide a fringing magnetic field between the poles which generates the longitudinal magnetic field in perpendicular recording media as the media travels under the perpendicular writing pole.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/175,266 filed Jan. 10, 2000 and U.S. Provisional Patent Application Ser. No. 60/248,517 filed Nov. 14, 2000. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to magnetic recording heads, and more particularly relates to perpendicular magnetic recording heads including a longitudinal magnetic field generator which facilitates magnetization switching of a perpendicular recording media during writing operations. 
     BACKGROUND INFORMATION 
     Magnetic hard disk drives incorporating longitudinal recording heads are well known. However, as the magnetic volumes of recording bits decrease to support higher areal bit densities, conventional longitudinal media are subject to superparamagnetic instabilities which limit recording densities. 
     Perpendicular recording heads which have been developed for use in hard disk drive systems may potentially increase recording densities in comparison with standard longitudinal recording heads. However, perpendicular designs may also be subject to limitations. 
     The magnetization switching of a recording bit in perpendicular magnetic recording may be a slower process than magnetization switching in longitudinal recording. The rate of media magnetization switching or rotation is determined by the magnitude of the torque applied to the magnetic moment of a bit, as defined by the equation:                 m          t       =     τ   =     γ                 m   ×     H   eff           ;                          
     where m is the magnetic moment and H eff  is the effective magnetic field with damping ignored. In longitudinal recording, several factors contribute to the cross product in this equation. Strong demagnetization fields at bit transitions (˜2πM s  of the media) are perpendicular to the plane of the disk (and to the direction of m). The fields generated by a standard longitudinal ring head have substantial perpendicular components (˜2πM s  of the yoke material). Also, since conventional longitudinal media is not oriented in the plane of the film, a substantial amount of the grains will have their hard axes oriented at angles far away from zero degrees, resulting in a non-zero cross product in the foregoing equation. Longitudinal designs thus provide fast rotation of the magnetization during switching. 
     The geometry is not as favorable in perpendicular recording. In conventional perpendicular head designs, the longitudinal component of the magnetic field is negligible. If the recording media is well aligned, the value of the cross product in the above equation is very small and thus the switching speed is slow. This raises serious concerns about recording dynamics in perpendicular recording systems. The present invention has been developed in view of the foregoing. 
     SUMMARY OF THE INVENTION 
     The present perpendicular recording head is designed to significantly improve dynamics of the recording process by generating a longitudinal magnetic field in the recording layer of the recording media which rotates the magnetization prior to writing. In an embodiment, this is accomplished by reducing the gap between the leading and trailing poles of the perpendicular recording head. 
     A feature of the present head design is the rotation of the recording fields to facilitate magnetization switching. The recording area, moving underneath the recording head, first sees the fringing fields generated in the gap of the recording head. These fields have both longitudinal and perpendicular components, e.g., both ˜2πM s  of the yoke material in magnitude. As used herein, the term “longitudinal magnetic field” includes fields generated in the perpendicular recording layer having a component parallel with the plane of the recording layer. The longitudinal component of the longitudinal magnetic field forces the magnetization in the recording layer to precess from its perpendicular or vertical orientation. By the time the perpendicular field (˜4πM s  of the yoke material) from the trailing pole of the writer reaches the recording area, the magnetization in the recording layer region to be written into is no longer perpendicular to the plane of the disk, thus leading to a non-zero cross-product. The gap width may be on the order of the distance between the air bearing surface (ABS) and the soft underlayer of the recording media. 
     An aspect of the present invention is to provide a perpendicular magnetic recording head comprising a trailing write pole and leading return pole, and means for rotating magnetization of a perpendicular magnetic recording media as the media passes under the recording head from the leading pole to the trailing pole. 
     Another aspect of the present invention is to provide a perpendicular magnetic recording head comprising a trailing perpendicular write pole, a leading return pole, and a gap between the write pole and return pole structured and arranged to generate a longitudinal magnetic field between the poles when magnetic flux is induced in the poles. 
     A further aspect of the present invention is to provide a perpendicular magnetic recording system comprising a perpendicular magnetic recording medium including a hard magnetic recording layer and a soft magnetic underlayer, and a perpendicular magnetic recording head positionable over the medium. The recording head comprises a trailing perpendicular write pole, a leading return pole, and a gap between the perpendicular write pole and return pole structured and arranged to generate a longitudinal magnetic field in the hard magnetic recording layer when magnetic flux is induced in the poles. 
     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 including a narrowed gap between the writing pole and return pole which generates a longitudinal magnetic field in accordance with an embodiment of the present invention. 
     FIG. 2 is a bottom view of the recording head of FIG.  1 . 
     FIGS. 3 a - 3   c  illustrate a magnetic data bit of a perpendicular recording disk as it passes under a perpendicular magnetic recording head of FIG.  1 . 
     FIG. 4 is a graph of perpendicular and longitudinal magnetic field profiles along a recording track of a magnetic disk which may be generated during operation of a recording head of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a partially schematic side view of a perpendicular magnetic recording head  10  in accordance with an embodiment of the present invention. The recording head  10  includes a trailing main write pole  12  and a leading return pole  14 . A yoke  16  connects the main pole  12  to the return pole  14 . An electrically conductive line  18 , shown in cross-section in FIG. 1, extends adjacent to the main pole  12 . An extension  20  extends from the return pole  14 . The main pole  12 , return pole  14 , yoke  16  and extension  20  are made of any suitable magnetically permeable material such as NiFe, FeAlN, FeTaN, CoFe, CoFeB, CoFeN or any other soft magnetic materials, including multiple layers of such materials. The conductive line  18  may be made of any suitable electrically conductive material such as Cu, Ag, Au or any other high conductivity materials or alloys. 
     As shown in FIG. 1, the recording head  10  is positioned over a recording disk  24  which travels in the direction of the arrow shown in FIG. 1 during recording operations. The disk  24  includes a substrate  25 , a soft magnetic underlayer  26 , a hard magnetic recording layer  27  and a protective layer  28 . The disk  24  may also include a magnetic decouple layer (not shown) between the soft underlayer  26  and recording layer  27 . The tip of the main pole  12  is positioned a distance H above the upper surface of the soft underlayer  26 . The end of the extension  20  is positioned a gap distance G from the main pole  12 . The height distance H and gap distance G may be within an order of magnitude of each other. The ratio of G:H may be from about 1:10 to about 10:1, for example, from about 1:1 to about 2:1. In an embodiment, the gap distance G may range from about 0.03 to about 0.5 micron, for example, from about 0.03 to about 0.1 micron. The height distance H may range from about 0.01 to about 0.05 micron, for example, from about 0.01 to about 0.02 micron. 
     As illustrated in FIG. 1, when current flows through the conductive line  18 , a magnetic field is induced in the write pole  12 . A portion of the induced magnetic field M travels from the tip of the write pole  12  perpendicularly through the recording layer  27 , then across the soft underlayer  26  and back to the return pole  14 . Another portion of the magnetic flux L travels from the tip and/or side of the main pole  12  to the extension  20 . The magnetic flux L generates a longitudinal magnetic field within or adjacent to the recording layer  27 . As more fully described below, the longitudinal magnetic field causes magnetization rotation within the recording layer  27  which facilitates subsequent perpendicular magnetic recording by the flux M from the tip of the main pole  12 . 
     FIG. 2 is a bottom view of the recording head  10  of FIG.  1 . The main pole tip  12  has a substantially smaller surface area A W  at the air bearing surface in comparison with the surface area A R  of the return pole  14 . The surface area A E  of the extension  20  at the air bearing surface may be greater than the surface area A W  of the tip of the main pole  12 , but less than the surface area A R  of the return pole  14 . 
     FIGS. 3 a - 3   c  schematically illustrate a magnetic data bit  30  within a track of the recording layer  27  as the bit  30  travels underneath the recording head  10 . For purposes of clarity, only the recording layer  27  and soft underlayer  26  of the recording disk are illustrated in FIGS. 3 a - 3   c . In FIG. 3 a , the bit  30  has an upward magnetization perpendicular to the plane of the recording layer  27 . As the bit  30  travels to the position shown in FIG. 3 b , the flux pattern L generates a longitudinal magnetic field within or adjacent to the bit  30 . The longitudinal magnetic field causes the magnetization of the bit  30  to rotate approximately 90 degrees to a direction substantially parallel with the plane of the recording layer  27 . Subsequently, the bit  30  travels to the position shown in FIG. 3 c . At this location, the magnetization of the bit  30  switches from the longitudinal orientation shown in FIG. 3 b  to a perpendicular orientation. Thus, as illustrated in FIGS. 3 a - 3   c , the longitudinal magnetic field generated by the flux pattern L causes the magnetization of the bit  30  to rotate to a substantially longitudinal orientation just before the bit  30  is written by the main pole  12 . 
     FIG. 4 shows perpendicular and longitudinal field profiles along the recording tack from a recording head in accordance with the present invention. As shown in FIG. 4, a significant longitudinal component of the field exists in the gap region. In accordance with the present invention, the longitudinal component of the field will cause magnetization in the recording layer to deflect from its equilibrium perpendicular or vertical orientation so that the vertical field under the trailing pole will act upon magnetization that is not vertically aligned. Thus, a significant torque can be developed to promote fast magnetization switching. 
     The present head is designed such that there is enough time for the trailing edge of the writing pole to reach the position above the recording media where the longitudinal component from the leading edge starts to switch the media in the period to time corresponding to the shortest switching cycle. For example, in a 30,000 rpm drive with a 3 cm disk radius and 1,000 Gflux/s recording rate, the distance traveled by the head relative to the disk surface in one cycle is about 0.1 micron. This constrains the maximum trailing pole thickness in the direction measured along the track. This constraint may be tightened or relaxed depending on the recording rate, the rotation speed and the radius at which the recording process occurs. 
     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.