Magnetic recording process

Details Magnetic recording process Magnetic recording process

2001-12-21

2004-10-19

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

General recording or reproducing

Specifics of biasing or erasing

C360S016000, C360S017000

Reexamination Certificate

active

06807025

ABSTRACT:

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 &Dgr;H) 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−&Dgr;H<Hmin, for regions covered by the mask, and
Ha+&Dgr;H>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.


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patent: 6545848 (2003-04-01), Terunuma
patent: 2001/0024342 (2001-09-01), Mitani et al.

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