Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
1999-03-16
2001-10-23
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Core
C360S321000
Reexamination Certificate
active
06307708
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exchange coupling film and a magnetic sensor having an exchange coupling film, and more particularly, to an exchange coupling film having magnetic anisotropy dispersion and a magnetic sensor having an exchange coupling film with magnetic anisotropy dispersion.
2. Discussion of the Background
Magnetic recording devices such as a Hard Disk Drive (HDD) are required to have a compact external form and high recording density. To achieve these requirements, the recording track width should be narrower for high widthwise density and high recording track lengthwise density.
A MagnetoResistance effect head (MR head) of high sensitivity in reproducing a magnetic signal from a magnetic recording medium of such high track widthwise density has been reported. The conventional MR head had an AnisotropicMagnetoResistance effect element (AMR element) and a Giant MagnetoResistance head (GMR head). That the GMR head can obtain higher sensitivity than the AMR head has also been reported.
The AMR or GMR head each coupled with a planar yoke body was introduced in pending U.S. patent application Ser. No. 08/815,179 which corresponds to Japanese Patent Publication (Kokai) 10-143821.
Referring to
FIG. 1
, MR film
27
is disposed on magnetic yokes (cores)
24
and also coupled to a pair of electrodes
30
. The magnetic yokes
24
are separated by a magnetic gap
25
at an Air Bearing Surface (ABS) which faces the magnetic recording medium. The magnetic yokes are disposed on magnetic shield film
22
formed on a substrate
21
. The MR film
27
is separated from the ABS and magnetic gap
25
at ABS is so thin that the required high track widthwise and lengthwise density is obtained by the head structure. A magnetic signal from the medium is picked up by the pole tip portions of the yokes separated by the gap
25
at the ABS and introduced to the MR film
27
. A resistance variation of the MR film
27
is sensed by a voltage detector coupled to the pair of electrodes
30
(not shown).
Magnetic domain walls
36
each surrounding a large magnetic domain of magnification direction transfer in the conventional magnetic yoke
24
as shown in FIG.
2
and the movement of the domain walls
36
produces an irreversible change in magnetization direction that the signal transmission in the core
24
may be discontinuous enough to raise the BaukHausen Noise (BHN). Such magnetic domain wall movement causing magnetic transfer in the conventional magnetic yoke
24
has a large influence because area of the yoke is up to 200 micrometer×200 micrometer and discontinuous signal transmission becomes a larger problem to magnetic variation than the one in a magnetic body having an area of 1 centimeter×1 centimeter.
FIG. 3
is data showing relation between external magnetic field (H) and magnetization (M) of the conventional magnetic core
24
recently obtained by the present invention (Delta Mb)/delta M) in every directions of the conventional magnetic core, which is around 30%, as shown in FIG.
3
. Where delta Mb is most drastic magnetization change which appears as BHN and equal to difference between the MB
1
and Mb
2
. Delta M is the magnetization range of the exchange coupling film ranging from negative saturation magnetization (minus M) to positive saturation magnetization (plus M), when external magnetic fields (H) are applied to the exchange coupling film. The M-H curve may be measured by a well known magnetization using the Kerr Effect. The M-H curve shows some drastic changes and most drastic change in the M-H curve is change at outer magnetic filed H
1
changing Mb
1
to Mb
2
like step.
SUMMARY OF THE INVENTION
It is an object of the present invention to obtain a magnetic core of smooth magnetic variation and provide a magnetic sensor, magnetic recording and/or reproducing head, and magnetic recording medium of high density and low BHN.
In a first aspect, the present invention provides an exchange coupling film, comprising: a ferromagnetic layer, and an antiferromagnetic layer disposed on the ferromagnetic layer. The antiferromagnetic layer is exchange coupled with the ferromagnetic layer and the exchange coupling film have a plurality of local magnetic regions. Each of the local regions has uniaxial magnetic anisotropy, and the uniaxial magnetic anisotropy of abutting local regions may be different from each other. The total magnetic anisotropy of the exchange coupling film is dispersed.
Each of the local regions of the ferromagnetic layer of the present invention is a small magnetic domain or magnetic region which receives unidirectional anisotropy magnetic fields from corresponding part of the antiferromagnetic layer which the ferromagnetic layer is exchange coupled with, and each of the small local regions has a magnetization fixed by the exchange coupling force. Therefore the irreversible magnetic transfer from the large domain walls surrounding the plurality of the small local regions in the ferromagnetic layer becomes suppressed and the magnetization characteristics become smooth enough that the magnetic anisotropy of the whole ferromagnetic layer becomes isotropic and the ferromagnetic layer has low BHN.
The local magnetic anisotropy may be introduced into the laminate film having the ferromagnetic layer and the antiferromagnetic layer by annealing or by depositing films in time-varying magnetic fields during some or each of the processing steps. A rotating magnetic field is one example of a time-varying magnetic field. These process steps are preferable for forming a magnetic circuit of isotropic permeability, such as a magnetic head.
(Delta Mb)/(delta M) in every directions of the exchange coupling film of the first aspect may be 10% or less which is much less than that of the conventional magnetic yoke, which is around 30%. Where delta Mb is most drastic magnetization change and equal to difference between the Mb
1
and Mb
2
. Delta M is the magnetization range of the exchange coupling film from negative saturation magnetization (minus M) to positive saturation magnetization (plus M), when external magnetic fields (H) are applied to the exchange coupling film. The M-H curve may be measured by a well known method using the Kerr Effect.
The local regions of the first aspect of the present invention have a small plane area of 10% or less compared to whole plane area of the ferromagnetic layer. A one-sided length of the local regions of the aspect of the present invention may preferably be 5 micrometer or less.
The magnetic permeability of the whole ferromagnetic layer of the first aspect of the present invention also be isotropic enough and it is preferable to form a closed magnetic circuit. When the exchange coupling film has a disc-like external shape, change in permeability measured by applying magnetic fields at plural directions to the exchange coupling film of the first aspect of the present invention may be in the range from minus 10% to plus 10%.
In the above described (delta Mb)/(delta M) characteristic, size of the local regions, and the permeability measurement characteristic of the first aspect of the present invention may also be applied to the following second to fourth aspects of the present invention.
The ferromagnetic layer of the first aspect of the present invention may comprise soft ferromagnetic materials, such as NiFe, FeAlSi, an amorphous Co alloy such as CoZrNb, a fine grain soft ferromagnetic materials such as FeZrN, a granular soft ferromagnetic materials such as CoFeAlO, and a soft ferrite material such as MnZn ferrite. Ferromagnetic materials such as FeZrN or CoFeAlO are preferable to obtain high saturation magnetic flux density. The antiferromagnetic layer may comprise IrMn, PdMn, FeMn, NiMn, NiO, and amorphous Fe2O3.
A ferromagnetic materials such as NiFe or CoZrNb and an antiferromagnetic material chosen from IrMn, PtMn, and NiMn are preferably matched to achieve high exchange coupling force. A granular soft ferromagnetic materials such as CoFeAlO or a soft ferrite such
Funayama Tomomi
Ohsawa Yuichi
Yoda Hiroaki
Yoshikawa Masatoshi
Evans Jefferson
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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