Dynamic magnetic information storage or retrieval – General recording or reproducing
Reexamination Certificate
2002-02-27
2003-12-16
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
C360S125330
Reexamination Certificate
active
06665136
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to recording heads for use with magnetic storage media, and more particularly, to such recording heads that utilize a single conductor for inducing a magnetic write field for longitudinal or perpendicular magnetic recording and to a method for recording data using such recording heads.
BACKGROUND OF THE INVENTION
Longitudinal and perpendicular recording heads for use with a magnetic storage medium are generally known. Longitudinal recording heads utilize a pair of opposing write poles with their tips in close proximity to each other at the bottom surface of the recording head. The two poles are connected at the top by a yoke, which may be made of a ferromagnetic material similar to that used for the poles. A coil having a plurality of turns is located in close proximity to one of the two opposing poles. When a current is passed through the coil, magnetic flux is induced in the yoke, which produces a magnetic field across a write gap, which separates the two poles. A portion of the magnetic flux across the write gap passes through the magnetic storage medium, thereby causing a change in the magnetic state within the magnetic storage medium where the head field is higher than the medium coercive force. The medium coercive force is chosen high enough so that only the head fields across a narrow gap between the poles, modify the bits of information on the storage medium.
The bits of information are recorded on the disc along concentric tracks that are separated by guard bands. The width of the track, plus that of the guard band in which no information is stored, defines the track density. The length of the bit along the track defines the linear density. The total storage capacity is directly proportional to the product of track density and linear density. Recording densities possible with longitudinal recording are believed to be limited to approximately 50 to 100 Gbit/inch
2
, because at higher recording densities, superparamagnetic effects result in magnetic instabilities within the magnetic storage medium.
Perpendicular recording has been proposed to overcome the recording density limitations of longitudinal recording. Perpendicular recording heads for use with magnetic storage media may include a pair of magnetically coupled poles, including a main write pole having a small bottom surface area and a flux return pole having a large bottom surface area. A coil having a plurality of turns is located adjacent to the main write pole for inducing a magnetic field between that pole and a soft underlayer. The soft underlayer is located below the hard recording layer of the magnetic storage medium and enhances the amplitude of the field produced by the main pole. This in turn allows the use of storage media with higher coercive force. Consequently, more stable bits can be stored in the medium. In the recording process, an electrical current in the coil energizes the main pole, which produces a magnetic field. The image of this field is produced in the soft underlayer to enhance the field strength produced in the magnetic medium. The magnetic flux emerges from the write pole tip, passes into the soft underlayer, and returns to the main pole through the return flux pole. The return pole is located sufficiently far from the main pole such that fringing flux between the main pole and the return pole does not affect the magnetization of the magnetic medium.
As bit-areal densities in magnetic recording continue to increase in an effort to increase the storage capacity of hard disc drives, magnetic transition (bit) dimensions and, concomitantly, recording head critical features are being pushed below 100 nm. A parallel effort to make the recording medium stable at higher areal densities requires magnetically harder (high coercivity) medium materials. Traditionally, writing to a harder medium has been achieved by increasing the saturation magnetization, or 4&pgr;M
s
value, of the magnetic material of the inductive write head, thus bolstering the magnetic field applied to the medium. Though there has been some success in materials research efforts to increase M
s
of the write head, the rate of increase is not significant enough to sustain the annual growth rate of bit areal densities in disc storage. A parallel effort to writing to progressively harder media is to locally reduce the coercivity of the media during the writing process. Typically, this would be accomplished by locally heating the medium (by optical, or, more generally, electromagnetic stimulation) to lower its temperature-dependent coercivity during the writing process. This technique has thus far been limited to proof of concept laboratory demonstrations, and requires numerous technological advances in both head design and disc materials. Accordingly, there is a need for a recording head that is capable of overcoming the coercivity of a magnetic medium appropriate for the next generation, and beyond, in recording technology, which has the benefit of manufacturability.
SUMMARY OF THE INVENTION
This invention provides a method of recording information bits in a magnetic storage medium, the method comprises positioning a first conductor adjacent to a magnetic recording medium, the conductor having a width and a length, wherein a distance between the first conductor and the magnetic recording medium is less than or equal to the width and the length, and passing a first current through the conductor of sufficient magnitude to produce a magnetic field in the magnetic medium greater than one Tesla and having a magnetic field gradient in the cross track direction and down track direction greater than 100 Oe
m over a bit dimension. The current density in the conductor can be greater than 10
9
ampere/cm
2
, and the length of the conductor can be less than 100 nm. The current can be applied as one or more pulses in a predetermined clock cycle time. The magnetic field can be augmented by using an additional conductor, an adjacent ferromagnetic film, and/or a magnetic yoke and coil. The first conductor can have a thickness that is less than the distance between the conductor and the magnetic recording medium.
The invention also encompasses a recording head for use with a magnetic storage medium, comprising a first conductor having a width and a length, means for positioning the first conductor adjacent to a magnetic recording medium, wherein a distance between the first conductor and the magnetic recording medium is less than or equal to the width and the length, and means for passing a first current through the first conductor of sufficient magnitude to produce a magnetic field in the magnetic medium greater than one Tesla and a magnetic field gradient in the cross track direction and down track direction greater than 100 Oe
m over a bit dimension. The recording head can further include a second conductor parallel to the first conductor, a ferromagnetic layer adjacent to the first conductor, a magnetic yoke structure, a means for reducing coercivity of the medium, or a combination of these structures.
Another aspect of the invention includes a magnetic disc drive storage system comprising a housing, means for supporting a magnetic storage medium positioned in the housing, and means for positioning a recording head adjacent to said rotatable magnetic storage medium, the recording head comprising a first conductor having a width and a length, wherein the distance between the first conductor and the magnetic recording medium is less than or equal to the width and the length, and means for passing a first current through the first conductor of sufficient magnitude to produce a magnetic field in the magnetic medium greater than one Tesla and a magnetic field gradient in the cross track direction and down track direction greater than 100 Oe
m over a bit dimension. The recording head can further include a second conductor parallel to the first conductor, a ferromagnetic layer adjacent to the first conductor, a magnetic yoke structure, a means for reducing coercivity of the medium, or a combination
Clinton Thomas William
Rottmayer Robert Earl
Seigler Michael Allen
Davidson Dan I.
Hudspeth David
Lenart, Esq. Robert P.
Pietragallo Bosick & Gordon
Seagate Technology LLC
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