Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
2002-09-05
2004-11-02
Letscher, George J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Core
Reexamination Certificate
active
06813115
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed toward magnetic recording heads and, more particularly, toward perpendicular magnetic recording heads having an improved write field gradient.
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 higher 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. Perpendicular recording is considered as one of the possibilities to achieve ultrahigh areal densities beyond conventional longitudinal recording.
Ultrahigh areal densities can be obtained in a perpendicular recording system by increasing the linear and/or track densities. For high linear densities, the transition parameter of a bit transition, as well as the transition jitter, need to be minimized. The actual values of the transition parameter and the transition jitter will depend upon both the properties of the recording medium and the on-track field gradient of the write head. In an ideal case, the write field gradient should be a step, i.e., an infinite slope of the field gradient, at the dynamic coercivity of the recording medium being used. In a similar manner, the track density that can be obtained will depend, in part, on the off-track field gradient of the write head.
One perpendicular recording system configuration, shown in
FIG. 1
, uses a single pole write head with a wide return pole and a recording medium which includes a magnetically soft underlayer and a magnetically hard recording layer, conventionally known as a double layered recording medium. As shown in
FIG. 1
, the magnetic recording head
10
has a single (main) pole
12
for generating a field at the recording media
14
, and is conventionally known as a single pole magnetic recording head. The magnetic recording head
10
includes the main pole
12
, a return pole
16
and a magnetic via
18
connecting the main
12
and return
16
poles. An electrically conductive magnetizing coil
20
surrounds the magnetic via
18
.
The recording media
14
typically includes a substrate
22
, a soft magnetic underlayer
24
formed on the substrate
22
and a perpendicularly magnetized recording layer
26
on top of the soft underlayer
24
. Additionally, the recording media
14
includes a spacing layer
28
between the soft underlayer
24
and the recording layer
26
, and thin layers of carbon overcoat
30
and lubricant
32
on top of the recording layer
26
. The carbon layer
30
is applied to the magnetic recording layer
26
and protects the magnetic recording layer
26
against damage from direct contact with the read/write head, and also serves as a corrosion barrier to prevent oxidation of the magnetic recording layer
26
. The lubricant layer
32
is applied to the carbon layer
30
and has viscous properties to produce sheer stresses between the read/write head and disc during contact.
When writing, the magnetic recording head
10
is separated from the recording media
14
by a distance conventionally known as the “fly height”. The recording media
14
is moved past the magnetic recording head
10
such that the recording head
10
follows the tracks of the recording media
14
. The track of the recording medium
26
on which information is being recorded in
FIG. 3
is denoted by
26
′. The coil
20
is traversed by a current and produces a magnetic flux
34
which is channeled by the main pole
12
to produce an intense writing flux at the tip
36
of the main pole
12
which records the information in the magnetic recording layer
26
′. The flux
34
passes from the tip
36
of the main pole
12
, through the magnetic recording layer
26
′, into the soft underlayer
24
, and across to the return pole
16
, which provides a return path for the flux
34
. Thus, a closed magnetic circuit is formed in which the magnetic flux in the recording layer
26
′ directly under the poles
12
,
16
of the magnetic recording head
10
is oriented perpendicular to the plane of the recording layer
26
. The cross-sectional area of the return pole
16
is larger than that of the main pole
12
to ensure that the flux density at the return pole
16
is sufficiently reduced as not to magnetize the recording layer
26
′.
By way of example, a perpendicular recording system proposed for an areal density of 100 Gbit/in
2
uses a single pole write (main) head
12
having a width of 130 nm and a thickness of 300 nm. A hard recording layer
26
thickness of 16 nm typically yields a total soft underlayer
24
to main pole
12
spacing of about 35 nm (which includes the spacing layer
28
, the overcoat
30
, the lubricant
32
and air).
As a consequence of the relatively large 35 nm spacing between the main pole
12
and the soft underlayer
24
as compared to the main pole
12
width of 130 nm and pole height of 300 nm, the maximum field in the write gap is reduced significantly from 4 &pgr;M
s
, the saturation magnetic flux density of the main pole
12
.
FIG. 2
illustrates a maximal on-track field (Hy) of about 1.2 Tesla for the conventional recording head
10
using a saturation magnetic flux density value of 2.0 Tesla. This results in a reduced write on- and off-track field gradient for recording head
10
. An additional consequence of the significant write gap relative to the dimensions of the main pole
12
is that the flux from the sides of the main pole
12
which are recessed from air bearing surface of the main pole
12
will contribute to the field at the write gap. This additional flux will degrade the write field gradient for both the on- and off-track directions. The flux arising from the magnetization at the air bearing surface of the main pole
12
, as well as from the sides of the main pole
12
, is schematically illustrated in FIG.
3
. The graph of
FIG. 4
illustrates the magnitude of the flux from the sides of the main pole
12
as the sides become further recessed from the air bearing surface of the main pole
12
. The general scaling trend of perpendicular recording towards Tbit/in
2
is such that the write field gradient will further deteriorate as the reduction in spacing between the main pole
12
and the soft underlayer
24
is small relative to reductions in the main pole
12
width and height.
An integral aspect of perpendicular recording is that the write field at the tip of the main pole is mainly perpendicular to the plane of the recording layer. It is known that the writeability, as well as the writing speed, of a perpendicularly magnetized grain depends upon the angle of the applied field to its uniaxial anisotropy axis, with perfect anti-parallel alignment being the worst. A small, longitudinal field component in the write field gradient will increase the writeability and write speed for a perpendicularly oriented grain without degrading the transition parameter, as long as the write field is primarily perpendicular to the recording layer.
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, i.e., a single pole magnetic recording head, and a coil magnetically coupled to the main pole for magnetizing the main pole in a first magnetization direction. The magnetic recording head further includes a layer of ferromagnetic material anti-ferromagnetically coupled to the main pole such that magnetization of the ferromagnetic layer is in a second magnetization direction substantially anti-parallel to the first magnetization direction of the main pole.
In one form, the
Batra Sharat
Hannay Jonathan D.
Parker Gregory
van der Heijden Petrus A.
Buchanan & Ingersoll PC
Letscher George J.
Magee Christopher R
Seagate Technology LLC
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