Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2001-01-10
2004-11-09
Letscher, George J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Core
C360S125330
Reexamination Certificate
active
06816339
ABSTRACT:
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:
ⅆ
m
ⅆ
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 (~2&pgr;M
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 (~2&pgr;M
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 ~2&pgr;M
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 (~4&pgr;M
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.
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Khizroev Sakhrat
Litvinov Dmitri
Letscher George J.
Magee C R
Pietragallo Bosick & Gordon
Towner, Esq. Alan G.
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