Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1998-11-13
2001-12-04
Ometz, David L. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06327121
ABSTRACT:
BACKGROUND OF THE INVENTION
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to a GMR head, a method for manufacturing such head, and a magnetic disk drive utilizing such head.
BACKGROUND OF THE INVENTION
In the 1990s, the bit-density of information on a magnetic disk has been extensively improved by a factor of 100 per 10 years. If this rate also holds for years to come, the bit density will be 10 G bits/in
2
by the year 2000 or 2001. Recent development in giant magnetoresistive (GMR) head technology seems to achieve this goal.
FIG. 1
shows an overall arrangement of a composite magnetic head
112
utilizing a GMR head for use in a magnetic disk drive, along with a magnetic medium
114
such as a magnetic disk positioned to face the composite head
112
. The composite magnetic head
112
shown herein is a merge type head having a “piggy backed structure”, which includes a write head
118
located on the back side of a read head
116
whose upper shield
120
also works as a lower write magnet (lower magnetic core)
120
for the write head
118
.
The GMR head
100
as shown in
FIG. 1
is included in the read head
116
. The GMR head comprises a GMR film
122
, a pair of electrodes
124
a
and
124
b
, a read lower shield
98
, and the upper read shield
120
, respectively, disposed on the opposite sides of the paired electrodes, respectively.
The write head
118
includes a write coil
128
, an organic insulation layer
130
surrounding the write coil
128
, a magnetic gap film
132
, and an upper write magnetic pole
134
disposed on the upper sides of the organic insulation layer
130
and the magnetic gap film
132
, and the lower write magnetic pole
120
disposed on the lower sides of the organic insulation layer
130
and the magnetic gap film
132
.
FIG. 2
shows a general arrangement of a GMR head
100
. The head
100
includes a spin valve film
122
which consists of a free magnetic layer
102
formed on a substrate
101
which comprises a lower gap film (not shown) formed on a read lower shield
98
(not shown), an intermediate layer
103
, a fixed or pinned magnetic layer
104
, and an antiferromagnetic or pinning layer
105
, as shown in FIG.
2
. The GMR head
100
comprises a spin valve film
122
and a pair of electrodes
124
a
and
124
b
(refer to
FIG. 1
) which are preferrably connected with at least the respective ends of the free magnetic layer
102
of the spin valve film
122
.
FIGS. 3A-D
explain how the electric resistance of the spin valve film
122
changes with magnetization therein. The spin valve film
122
has four layers as shown in FIG.
3
A. The two magnetic layers (free and pinned layers)
102
and
104
are intervened by the intermediate non-magnetic layer
103
. Provided on the pinned magnetic layer
104
is the antiferromagnetic layer
105
, thereby pinning the magnetization Mp in the layer
104
adjacent to the antiferromagnetic layer
105
in the same direction as the magnetization in the boundary or interface region of the antiferromagnetic layer
105
after annealing.
On the other hand, the free magnetic layer
102
, separated by the intermediate layer
103
, does not assume magnetization in a fixed orientation. In other words, the pinned magnetic layer
104
has a high pinning force or coercivity, while the free magnetic layer
102
has a low pinning force or coercivity, as shown in FIG.
3
C.
Under the influence of an external magnetic field, the free magnetic layer
102
is magnetized to the external magnetic field direction, acquiring some magnetization Mf in a direction. It is known that when the magnetizations in the free magnetic layer
102
and pinned magnetic layer
104
make an angle of 180° (that is, they are pointing in the opposite directions, as shown in FIG.
3
A), the electric resistance in the spin valve film reaches its maximum.
FIGS. 4A and B
illustrate the principle lying behind the GMR head. As shown in
FIG. 4A
, if the free magnetic layer
102
and the pinned magnetic layer
104
have their magnetization in mutually opposite directions, electrons traveling from one layer into another are likely to be scattered in relatively large numbers by the interlayer between the (non-magnetic) intermediate layer and the magnetic layer, thereby exhibiting high resistivity.
If the magnetization in the free magnetic layer
102
coincides with that in the pinned magnetic layer
104
as shown in
FIG. 4B
, the scattering of the electrons traveling across the interface layer, or the boundary, between the intermediate (non-magnetic layer) and the magnetic layer is in relative small numbers. To add a further explanation, the traveling electrons each have either a spin up and a spin down, but one of them is more strongly scattered by a given magnetic field. In
FIGS. 4A and B
, scattering of electrons have occurred, but it is less likely that electrons are scattered in the case shown in
FIG. 4B
as compared with
FIG. 4A
, thereby controlling electrons to flow from the pinned magnetic layer
104
into the free magnetic layer
103
.
As shown in
FIG. 3D
, the magnetization Mf in the free magnetization layer of a GMR element having a spin valve structure is varied by the externally applied magnetic field, which is a magnetic field Hsig representative of a signal in the example shown herein. The change in the magnetization in turn results in a change in resistance of the spin valve film
122
of the GMR element in proportion to the cosine of the relative angle theta (&thgr;) between the magnetizations Mf and Mp in the respective free and pinned magnetic layers
102
and
104
, respectively, in the range from 0° to 180°.
Accordingly, in a magnetic head utilizing such GMR film
122
, if the magnetization Mf in the free magnetic layer
102
is set up in the direction perpendicular (90°) to the fixed or pinned magnetization Mp in the pinned magnetic layer
104
under no externally applied magnetic field, the resistance under an externally applied magnetic field (e.g. signal magnetic field Hsig) will change substantially linearly and symmetrically in the range from 0° to 180°, with a mean value found at theta (&thgr;)=90°. Such symmetrical response in resistance facilitates processing of read signals from the magnetic disk drive.
In an actual spin valve element, however, the free magnetic layer
102
is influenced by not only the externally applied signal magnetic field Hsig, but also a number of noise fields that arise from, for example, the exchange coupling of the magnetic fields of the free magnetic layer
102
and pinned magnetic layer
104
, a magnetic field that arises from magnetic poles appearing on the end faces of the pinned magnetic layer
104
, and a magnetic field caused by a sense current through the GMR element. As a result, the magnetization in
102
is deviated away from the direction of X axis (along the width of the element), thereby causing the electric resistance of the element to change substantially nonlinearly and non-symmetrically.
In order to orient the magnetization Mf in free magnetic layer
102
along X axis (along the width of the layer) when it is free of any externally applied magnetic field, it is necessary to provide an additional magnetic field, called a biasing field, to cancel out the Y components of the noise fields.
The biasing field depends on the magnitudes and the directions of the noise field. A GMR head element is preferably designed to minimize the required level of such biasing field.
On the other hand, the width w (i.e. dimension in X direction) of a GMR head is determined in accordance with the recording bit density on the magnetic recording medium so that the spin valve element may cover a track on the medium (
FIG. 1
) and accurately read bit data stored thereon. Hence, the width must have a sufficiently small dimension for the recording magnetic medium with increased bit density.
It is noted that if the height h (the size in the Y direction) of the element is much shorter than the width w, the magnetization Mf in the free magnetic layer
102
tends to b
Kishi Hitoshi
Kondoh Reiko
Nagasawa Keiichi
Shimizu Yutaka
Tanaka Atsushi
Castro Angel
Fujitsu Limited
Greer Burns & Crain Ltd.
Ometz David L.
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