Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2002-03-15
2004-04-27
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Core
C360S123090
Reexamination Certificate
active
06728065
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed toward magnetic recording heads and, more particularly, toward magnetic recording heads designed to minimize write asymmetry.
BACKGROUND OF THE INVENTION
The ability to increase the storage capacity in magnetic recording is an ongoing concern. As the amount of information to be stored continues to increase, demands for high density recording also continue to increase. In conventional longitudinal magnetic recording systems, as areal densities approach 100 Gbit/in
2
it has become increasingly difficult to meet the requirements of thermal stability (the degradation of written information due to thermal fluctuations), SNR(Signal-To-Noise Ratio) and writeability. Improving on one of the requirements typically results in a tradeoff negatively effecting another requirement. For example, while the SNR can be increased by reducing the grain size of the recording medium, which is normally 200 Å thick, reducing the grain size of the media results in a decrease in thermal stability. While the thermal stability can be increased by increasing the anisotropy of the recording medium, e.g., using a different alloy, this results in a decrease in writeability. While reducing the Bit Aspect Ratio (BAR) has been proposed to extend longitudinal recording up to 100 Gbit/in
2
, the above-identified problems remain as fundamental limitations inherent in conventional longitudinal magnetic recording systems.
As the longitudinal magnetic recording technology reaches its limit in areal density due to thermal stability, SNR and writeability requirements, perpendicular magnetic recording systems (in which the recording medium is magnetized in a direction perpendicular to the plane of the recording medium) have been proposed to possess the potential for higher recording densities. Various modeling and simulations have suggested that perpendicular recording is superior to conventional longitudinal recording due to various reasons, including, but not limited to, larger optimal medium thickness, better write field efficiency, and less demagnetizing fields from the stored bit patterns. Perpendicular recording, coupled with the use of a soft under-layer media, is considered a strong candidate to extend recording densities by achieving sharp transitions, even with the use of a thicker magnetic recording layer. With the soft under-layer media, stronger recording fields can be generated, which in turn allow the use of higher anisotropy media. The higher anisotropy media, coupled with the thicker magnetic recording layer, is projected to provide a gain of a factor of 5-10 in recording densities for the same thermal stability criterion.
FIG. 2
illustrates a typical example of a conventional perpendicular magnetic recording head, shown generally at
10
. The magnetic recording head
10
has a single (main pole) pole for generating field at the media
11
, and is conventionally known as a single pole magnetic head. The magnetic recording head
10
includes a main pole
12
, a return pole
14
and a magnetic via
15
connecting the main
12
and return
14
poles. An electrically conductive magnetizing coil
16
surrounds the magnetic via
15
. The recording media
11
typically includes a substrate
18
, a soft magnetic underlayer
20
formed on the substrate
18
, and a perpendicularly magnetized recording layer
22
formed on the soft underlayer
20
.
When writing, the magnetic recording head
10
is separated from the recording media
11
by a distance known as the “fly height”. The recording media
11
is moved past the magnetic recording head
10
so that the recording head
10
follows the tracks of the recording media
11
. The coil
16
is transversed by a current and produces a magnetic flux
24
channeled by the main pole
12
to produce an intense writing flux at the tip
26
of the main pole
12
which records the information in the magnetic recording layer
22
. The flux
24
passes from the tip
26
of the main pole
12
, through the magnetic recording layer
22
, into the soft underlayer
20
, and across to the return pole
14
, which provides a return path for the flux, thereby forming a closed magnetic circuit in which the magnetic flux in the recording layer
22
directly under the poles of the magnetic recording head
10
is oriented perpendicular to the plane of the recording layer
22
. The cross-sectional area of the return pole
14
is larger than that of the main pole
12
to ensure that the flux density at the return pole
14
is sufficiently reduced as not to magnetize the recording layer
22
.
While perpendicular recording has its advantages over longitudinal recording, the use of the soft underlayer
20
poses some challenges during writing as well as reading. Because of the relatively high permeability of the soft underlayer, transitions previously recorded on adjacent tracks can influence the transitions being written at the main pole
12
. Depending on the magnetization state of the tracks adjacent to the written track, an asymmetry is introduced in the written di-bit response. This is typically referred to as the “neighborhood effect”.
FIG. 1
shows two written di-bits, at
26
and
28
, separated by an isolated transition, at
30
, using a conventional single pole perpendicular recording head on a recording media with a soft underlayer. Three different states of magnetization of the neighboring track are illustrated in
FIG. 1
, namely, AC erase (neighboring track not magnetized), DC erase (+) (neighboring track magnetized upward) and DC erase (−) (neighboring track magnetized downward). As shown in
FIG. 1
, depending on the magnetization state of the neighboring track, i.e, DC erase (+) or DC erase (−), an asymmetry is seen in the corresponding di-bit pattern. This asymmetry is illustrated in both a change in amplitude of the measured flux and a time shift in the written di-bit pattern. The time shift asymmetry in the di-bit pattern and the amplitude asymmetry in the amplitude of the di-bits shows as a measurable time shift for an isolated transition. Since the magnetization pattern from the neighboring tracks changes depending on the data stored on the neighboring tracks, this will change the di-bit asymmetry. This asymmetry will effect the performance of linear channels and degrade the areal density that can be achieved by those linear channels. Further, the effects of the di-bit pattern asymmetry become even more evident at smaller track widths, i.e., higher areal densities.
Additionally, stray magnetic fields from the other components in the disc drive also can corrupt the recorded information. These stray magnetic fields couple with the main pole
12
of the recording head
10
and either add to or subtract from the write field, producing further written asymmetry and transition shifts.
The present invention is directed toward overcoming one or more of the above-mentioned problems.
SUMMARY OF THE INVENTION
A single pole magnetic recording head is provided according to the present invention for perpendicular magnetic recording on a recording medium. The magnetic recording head includes a main magnetic pole having a first end positionable adjacent the recording medium and a second end spaced from the first end. A coil is magnetically coupled to the main magnetic pole for producing a write flux. The magnetic recording head further includes a magnetic return pole forming first and second return paths for the magnetic flux. The magnetic return pole includes first and second return poles disposed on opposite sides of, and spaced from, the main magnetic pole, and a magnetic via connecting the first and second return poles and extending over the main magnetic pole forming a back shield. The main magnetic pole is isolated from the magnetic return pole by a control gap of non-magnetic material between the second end of the main magnetic pole and the magnetic via to effectively isolate the main magnetic pole from the magnetic return pole.
In one form, the magnetic return pole is formed of a magnetic mate
Batra Sharat
Parker Gregory
Van der Heijden Petrus Antonius
Buchanan Ingersoll P.C.
Evans Jefferson
Seagate Technology LLC
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