Abstract:
A magnetic recording process includes applying an initial magnetic field to magnetize a magnetic recording medium and positioning a ferromagnetic mask over the magnetic recording medium. The ferromagnetic mask has a tooth which shields a portion of the magnetic recording medium in order to maintain the initial magnetic field in the portion. The process also includes applying a biasing magnetic field to the magnetic recording medium and applying a recording magnetic field to the magnetic recording medium while applying the biasing magnetic field. The biasing magnetic field is substantially perpendicular to the initial magnetic field and the recording magnetic field is substantially opposite in polarity to the initial magnetic field.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation-in-part (and claims the benefit of priority under 35 U.S.C. §120) of U.S. patent application Ser. No. 10/022,566, filed on Dec. 14, 2001, now abandoned. 
    
    
     TECHNICAL FIELD 
     This invention relates a process for recording information onto a magnetic recording medium. 
     BACKGROUND 
     A magnetic medium contains magnetic particles that can be polarized by application of a magnetic field. The magnetic medium is characterized by a hysteresis curve, which specifies the magnitudes of magnetic fields needed to change the polarization of the magnetic particles. For example, in the hysteresis curve shown in FIG. 1, a magnetic field above H max  will result in a change in polarization of most all magnetic particles in the medium. A magnetic field having a magnitude below H min  will cause virtually no change in polarization. 
     Information, such as a servo pattern, is recorded onto a magnetic recording medium by placing a mask (having a magnetic shield value of ΔH) over the medium and applying a magnetic field, H a . The medium is then re-magnetized such that portions of the medium covered by the mask retain their original polarity and portions of the medium that are not covered by the mask obtain a new polarity. 
     To reduce the occurrences of spurious subpulses, i.e., regions of improper polarity, on the recording medium, the following two conditions should be met: 
     Ha−ΔH&lt;Hmin, for regions covered by the mask, and 
     Ha+ΔH&gt;Hmax, for regions uncovered by the mask. 
     That is, for covered regions (i.e., regions covered by the mask), the difference between the applied magnetic field and the magnetic shield of the mask should be less than H min  on the hysteresis curve, resulting in few, if any, changes in polarity in those regions. For uncovered regions (i.e., regions not covered by the mask), the sum of the applied magnetic field and the magnetic shield of the mask should be greater than H max  on the hysteresis curve, resulting in substantial, if not total, changes in polarity. 
     SUMMARY 
     In general, in one aspect, the invention is directed to a method for use in recording information on a medium. The method includes applying a first magnetic field to the medium, applying a second magnetic field to the medium, the second magnetic field being substantially perpendicular to the first magnetic field, and applying a third magnetic field to the medium, the third magnetic field being substantially opposite in polarity to the first magnetic field. By applying magnetic fields in this manner, it is possible to re-orient magnetic grains on the recording medium and thereby reduce the magnetic field needed to record information onto the medium. 
     This aspect may include one or more of the following features. The first magnetic field may orient magnetic grains in the medium towards a first direction. The second magnetic field may orient the magnetic grains towards a second direction that is perpendicular to the first direction. The third magnetic field may orient the magnetic grains towards a third direction that is opposite to the first direction. The first direction may be an X direction in a three-dimensional Cartesian XYZ coordinate system. The second direction may be a Z direction in the three-dimensional Cartesian XYZ coordinate system. The third direction may be a −X direction in the three-dimensional Cartesian XYZ coordinate system. 
     The second magnetic field may have sufficient strength to orient at least some of the magnetic grains at least 10° towards the Z direction. The second magnetic field may have sufficient strength to orient a majority of the magnetic grains to 45°±10° towards the Z direction. 
     The method may include positioning a mask over the medium. The mask may have a tooth that shields a portion of the medium underneath the tooth in order to maintain the first magnetic field in the portion underneath the tooth. The information may include a servo pattern to be recorded on the medium and the tooth may define a portion of the servo pattern. The mask may be made of a ferromagnetic material, such as cobalt, having teeth that define a servo pattern to be recorded on the medium. Applying the second magnetic field may change a squareness of the medium. 
     In general, in another aspect, the invention is directed to a magnetic recording process that includes applying an initial magnetic field to magnetize a magnetic recording medium and positioning a ferromagnetic mask over the magnetic recording medium. The ferromagnetic mask may have a tooth that shields a portion of the magnetic recording medium in order to maintain the initial magnetic field in the portion. The method also includes applying a biasing magnetic field to the magnetic recording medium, the biasing magnetic field being substantially perpendicular to the initial magnetic field, and applying a recording magnetic field to the magnetic recording medium while applying the biasing magnetic field, the recording magnetic field being substantially opposite in polarity to the initial magnetic field. 
     This aspect may include one or more of the following features. The initial magnetic field may cause magnetic grains in the magnetic recording medium to orient towards a first direction. The recording magnetic field may cause magnetic grains in the magnetic recording medium that are not located underneath the tooth to orient towards a second direction that is different from the first direction. The second direction may have a directional component that is opposite to a directional component the first direction. Orienting the magnetic grains in the second direction may include recording information on the magnetic recording medium. Applying the biasing magnetic field may cause magnetic grains in the magnetic recording medium to orient towards a direction that is perpendicular to a direction of the initial magnetic field and the recording magnetic field. 
     The initial magnetic field may orient magnetic grains in the magnetic recording medium towards an X direction in a three-dimensional Cartesian XYZ coordinate system. The biasing magnetic field may orient magnetic grains in the magnetic recording medium towards a Z direction in the three-dimensional Cartesian XYZ coordinate system. The recording magnetic field may orient magnetic grains in the magnetic recording medium towards a −X direction in the three-dimensional Cartesian XYZ coordinate system. 
     The biasing magnetic field may have sufficient strength to orient at least some of the magnetic grains to at least 10° towards the Z direction. The biasing magnetic field may have sufficient strength to orient a majority of the magnetic grains to 45°±10° towards the Z direction. 
     The ferromagnetic mask may define a servo pattern to be recorded on the magnetic recording medium and the tooth may define a portion of the servo pattern. The mask may include plural teeth that define a servo pattern to be recorded onto the magnetic recording medium. The ferromagnetic material may include cobalt. Applying the biasing magnetic field may change a squareness of the magnetic recording medium. 
     In general, in another aspect, the invention is directed to a disk drive that includes a disk having a plurality of concentric tracks which store data and a print head which transfers data to and from the concentric tracks of the disk. The disk also includes servo information that is applied to the disk by applying a first magnetic field to the disk, applying a second magnetic field to the disk, the second magnetic field being substantially perpendicular to the first magnetic field, and applying a third magnetic field to the disk, the third magnetic field being substantially opposite in polarity to the first magnetic field. 
     This summary has been provided so that the nature of the invention can be understood quickly. A description of illustrative embodiments of the invention is set forth below. 
    
    
     DESCRIPTION OF DRAWINGS 
     FIG. 1 is a graph showing a hysteresis curve for a magnetic recording medium. 
     FIG. 2 a flowchart showing a magnetic recording process. 
     FIGS. 3,  5  and  13  show polarities of magnetic grains on the magnetic recording medium. 
     FIGS. 4,  6 ,  8 ,  11  and  14  are side views of a magnetic recording medium being subjected to the process of FIG.  2 . 
     FIG. 7 is a top view of teeth in a mask used in the process of FIG.  2 . 
     FIGS. 9 and 10 show the effect of a perpendicular magnetic field on a magnetic grain in the magnetic recording medium. 
     FIG. 12 is a graph showing the effect on a magnetic recording medium of applying the perpendicular magnetic field to the recording medium prior to recording. 
     Like reference numerals in different figures indicate like elements. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 2, a process  10  is shown for recording information onto a magnetic recording medium. Process  10  may be implemented using standard recording equipment, including a computer to control the process. 
     Process  10  will be described with respect to the magnetic recording medium  11  shown in FIG.  3 . Magnetic recording medium  11  may be any type of medium, such as tape or a disk, that is capable of storing data using a magnetic field. As shown in FIG. 3, magnetic recording medium  11  is comprised of magnetic grains  12 . Prior to application of an external magnetic field, magnetic grains  12  are randomly polarized, i.e., they do not point generally towards a single direction. The direction of polarization is indicated by the arrows disposed along the axes of magnetic grains  12 . 
     In this regard, each magnetic grain includes an “easy axis”, such as easy axis  14  of grain  12   a . In this context, the easy axis of a magnetic grain is an axis on which the poles of the grain lie naturally. The easy axes of the magnetic grains in a recording medium generally lie along the same plane. In the description that follows, this plane is defined to be the Cartesian XY plane, as shown in FIG.  3 . That is, the X and Y directions are the horizontal and vertical, respectively, along the recording medium and the Z direction, where applicable, is pointing “out of” and “into” the page on the plane of FIG.  3 . 
     At the start of process  10 , magnetic recording medium  11  is polarized so that its magnetic grains are oriented generally towards the same direction. Referring to FIG. 4, polarization is achieved by applying ( 201 ) an initial magnetic field  15 , H i , to magnetic recording medium  11 . The direction of the initial magnetic field H i  is shown by the arrows. In this example, the direction of H i  is +X, as shown. 
     Polarization, in this context, does not mean that all of the magnetic grains are polarized in exactly the same manner, i.e., that all the arrows point in exactly the same direction. Rather, as shown in FIG. 5, the magnetic grains  12  remain generally polarized along their easy axes. However, the polarizations are such that the poles of each grain, except for those grains having easy axes solely in the Y direction, are oriented in the same direction. For example, the arrows in FIG. 5 defining the grains polarities have a +X component (except for those that lie in the Y-direction only), meaning that the grains are polarized in generally the same direction (the direction of H i ). By way of example, refer to magnetic grain  12   b . The easy axis of magnetic grain  12   b  is angled roughly 45° relative to X-axis  16 . The polarity of magnetic grain  12   b  is switched so that the grain points generally in the +X direction. 
     Referring to FIG. 4, following application of the initial magnetic field, H i , recording medium  11  is polarized in the direction shown by the arrows. A ferromagnetic mask  17  (FIG. 6) is then positioned ( 202 ) over the magnetized recording medium  11 . Ferromagnetic mask  17  may be a cobalt-based mask that acts as a magnetic shield for magnetized recording medium  11 . Ferromagnetic materials other than cobalt may be included in, or used for, the mask. 
     Ferromagnetic mask  17  has a magnetic shield value of ΔH. Ferromagnetic mask  17  prevents a change in polarity of portions of recording medium  11  underneath mask  17  (i.e., covered by mask  17 ) up to a value of ΔH. In this embodiment, ferromagnetic mask  17  is comprised of teeth  19  that come into contact with recording medium  11 . The teeth provide the shielding ΔH in areas of contact with recording medium  11 . 
     In this embodiment, the teeth  19  are arranged on ferromagnetic mask  17  to define a servo pattern (FIG. 7) to be recorded onto recording medium  11 . A servo pattern is used during magnetic recording to keep track of, and re-position (if necessary), a recording head on the recording medium. During recording, the teeth shield portions of recording medium  11  that they cover, thereby preventing those portions from being re-polarized and maintaining the initial magnetic field, H i , in the portions. The uncovered (unshielded) portions of recording medium  11  are re-polarized during recording. The re-polarized portions comprise the servo pattern on the recording medium. 
     Referring to FIG. 8, a biasing magnetic field, H p , is applied ( 203 ) to recording medium  11  (with mask  17  still in place over recording medium  11 ). Biasing magnetic field H p  is substantially perpendicular to the initial magnetic field H i . Referring to FIG. 9, biasing magnetic field H p  is in a Z direction in Cartesian XYZ space, the −Z direction to be specific. It is noted that H p  and H i  need not be exactly perpendicular, but should contain at least perpendicular components sufficient to orient the magnetic grains in the +Z direction (depending on the direction of the H p  field). 
     Applying the biasing magnetic field orients the magnetic grains in recording medium  11  towards a Z (in this case, −Z) direction. This is depicted in FIGS. 9 and 10. More specifically, as shown in FIG. 10, the easy axis of magnetic grain  12   a  lies in the XY plane. Applying a Z-direction biasing magnetic field H p  to magnetic grain  12   c  causes the easy axis of the grain to tilt downward, such that the easy axis (and thus the magnetic poles of the magnetic grain) is oriented towards the −Z direction. That is, applying H i  and H p  to magnetic grain  12   a  produces a resultant vector  21  that defines the orientation of the easy axis of magnetic grain  12   a and an angle, θ, that defines the amount of orientation of the magnetic grain towards the Z-axis. In one embodiment, biasing magnetic field H p  has sufficient strength to orient at least some of the magnetic grains in a recording medium at least 10° (i.e., θ in FIG. 10) towards the Z direction. In another embodiment, biasing magnetic field H p  has sufficient strength to orient a majority of the magnetic grains in the recording medium to 45°±10° towards the Z direction. 
     Information is recorded onto recording medium  11  by applying ( 204 ) a recording magnetic field H a  to the medium. Referring to FIG. 11, the recording (applied) magnetic field, H a , is opposite in direction to the initial magnetic filed, H i . H a  is of a sufficient magnitude to change the polarity of magnetic grains in recording medium  11  that are not covered by ferromagnetic mask  17 . In this embodiment, the recording magnetic field is applied while applying the biasing magnetic field. The magnitude of H a  is set so that the following two conditions are met: 
     Ha−ΔH&lt;Hmin, for regions covered by the mask, and 
     Ha+ΔH&gt;Hmax, for regions uncovered by the mask. 
     Applying H p  reduces H max , thus increasing the squareness of recording medium  11 . “Squareness”, in this context, refers to the shape of the medium&#39;s hysteresis curve. The closer H max  and H min  are to one another, the more “square” the recording medium defined by the curve is. Since H max  is lower following application of H p , lower H a  and ΔH values can be used for magnetic recording. 
     In more detail, magnetic grains that are polarized oppositely to H a  are more difficult to switch during printing than magnetic grains that are offset relative to H a . Applying H p  to recording medium  11  offsets the magnetic grains relative to H a . This has the effect of reducing H max  for the material (since the offset makes it possible to use a smaller magnetic field to switch the polarity of the magnetic grains). Referring to FIG. 12, by re-orienting the grains by 45° along the Z-direction, the amount of applied magnetic field, H a , required to reverse the polarity of the grains is cut in half. As shown in FIG. 12, increasing the angle, also increases the amount of magnetic field required to reverse the polarity of the grains. 
     FIG. 13 shows the easy axes of grains  12  following application of Ha (for those portions of the recording medium that are not shielded). FIG. 14 shows the polarities of the various portions  31  to  35  of recording medium  11  following printing. As shown, portions  32  and  34  have the polarity of applied magnetic field H a  and portions  31 ,  33  and  35  have the polarity of initial magnetic filed H i . Portions  32  and  34  constitute the servo pattern on recording medium  11 . 
     Process  10  can be used to write servo data to a magnetic disk in a disk drive (not shown). The magnetic disk, in general, contains a plurality of concentric tracks for storing digital data and servo spokes for storing servo information. The servo information is stored on the tracks of the disk via, e.g., process  10 , in the form of magnetic polarity transitions induced into a magnetic layer covering the disk. 
     During operation of the disk drive, the disk is rotated about an axis by a spin motor at a substantially constant angular speed. To perform a transfer of data with the disk, a transducer, known as a print (or “recording”) head, is centered above a track of the rotating disk. Once centered, the head can be used to transfer data to the track (during a write operation) or to transfer data from the track (during a read operation). During writing, a write current is delivered to the centered head to create an alternating magnetic field (the recording magnetic field noted above) in a lower portion of the head that induces magnetic polarity transitions onto the track. During reading, the centered head senses magnetic fields emanating from the magnetic polarity transitions on the moving track to create an analog read signal representative of the data thereon. 
     The invention is not limited to the specific embodiments described above. For example, the invention is not limited to recording servo patterns or to recording the servo patterns onto disks or tape. The invention is not limited to using a ferromagnetic mask. Any type of mask that will provide a magnetic shield can be used. The invention is not limited to the specific geometries and/or to the directions of the magnetic fields described herein. These may be varied so long as their counterparts are varied correspondingly in accordance with the teachings set forth herein. 
     Other embodiments not described herein are also within the scope of the following claims.