Dynamic magnetic information storage or retrieval – Head – Core
Reexamination Certificate
1999-07-22
2002-02-12
Cao, Allen T. (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Core
C360S314000
Reexamination Certificate
active
06347022
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dual spin-valve type magnetoresistive thin film element in which electrical resistance changes in response to the relationship between the magnetization direction of pinned magnetic layers and the magnetization direction of a free magnetic layer that is influenced by an external magnetic field. More particularly, the invention relates to a spin-valve type magnetoresistive thin film element in which satisfactory asymmetry can be obtained while maintaining a high rate of resistance variation, and to a spin-valve type magnetoresistive thin film head using the same.
2. Description of the Related Art
A spin-valve type magnetoresistive thin film element is a kind of giant magnetoresistive (GMR) element which uses a giant magnetoresistance effect, in which a high rate of resistance variation can be obtained in a relatively simple structure. Among spin-valve type magnetoresistive thin film elements, a single spin-valve type magnetoresistive thin film element has the simplest film structure, which includes 4 layers consisting of an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic electrically-conductive layer, and a free magnetic layer. A dual spin-valve type magnetoresistive thin film element has a film structure in which a higher rate of resistance variation can be obtained in comparison with the single spin-valve type magnetoresistive thin film element.
FIG. 10
is a sectional view of a conventional dual spin-valve type magnetoresistive thin film element, taken from the surface facing a recording medium.
As shown in
FIG. 10
, on either surface of a free magnetic layer
1
, a nonmagnetic electrically-conductive layer
2
, a pinned magnetic layer
3
, and an antiferromagnetic layer
4
are deposited in that order symmetrically, and on either side of the laminate, a hard magnetic bias layer
5
and a lead layer
8
are formed. Numeral
6
represents an under layer composed of a metal, such as Ta, and numeral
7
represents a protective layer composed of Ta or the like.
As shown in
FIG. 10
, the pinned magnetic layers
3
and
3
are formed in contact with the antiferromagnetic layers
4
and
4
, and the magnetizations of the pinned magnetic layers
3
and
3
are fixed in the Y direction (depth direction) by exchange coupling magnetic fields generated at interfaces between the pinned magnetic layers
3
and
3
and the antiferromagnetic layers
4
and
4
.
The hard magnetic bias layers
5
and
5
are magnetized in the X direction in the drawing (track width direction), and the magnetization of the free magnetic layer
1
is set in the X direction under the influence of biasing magnetic fields from the hard magnetic bias layers
5
and
5
.
In the dual spin-valve type magnetoresistive thin film element, a sensing electric current is applied in the X direction from the lead layer
8
to the free magnetic layer
1
, nonmagnetic electrically-conductive layers
2
and
2
, and pinned magnetic layers
3
and
3
. A magnetic recording medium such as a hard disk moves in the Z direction, and when a fringing magnetic field from the recording medium is applied in the Y direction, the magnetization of the free magnetic layer
1
changes from being in the X direction to being in the Y direction. There is a change in electrical resistance in response to the relationship between the change in the magnetization direction of the free magnetic layer
1
and the fixed magnetization direction of the pinned magnetic layers
3
and
3
, and thus, the fringing magnetic field is detected.
In the conventional dual spin-valve type magnetoresistive thin film element, as shown in
FIG. 10
, the nonmagnetic electrically-conductive layers
2
and
2
which are formed on upper and lower surfaces of the free magnetic layer
1
, respectively, have the same thickness h
1
, the pinned magnetic layers
3
and
3
are formed at the same thickness h
2
, and the antiferromagnetic layers
4
and
4
are also formed at the same thickness h
3
. That is, the conventional dual spin-valve type magnetoresistive thin film element has a structure in which laminates sandwiching the free magnetic layer
1
are perfectly symmetrical.
However, in the dual spin-valve type magnetoresistive thin film element having a vertically symmetrical structure, the magnetization direction of the free magnetic layer
1
is not stabilized, and it is very difficult to obtain satisfactory asymmetry (vertical asymmetry of the regenerated output waveform).
FIG. 11
is a longitudinal sectional view which schematically shows a spin-valve type magnetoresistive thin film head, including the dual spin-valve type magnetoresistive thin film element shown in
FIG. 10
, and a pair of shield layers. A sensing electric current
9
from the lead layer
8
flows perpendicularly with respect to the drawing toward the front.
As shown in
FIG. 11
, various magnetic fields are applied to the free magnetic layer
1
. First, interlayer coupling magnetic fields Hbf
1
and Hbf
2
(interlayer exchange coupling+topological coupling) occur between the pinned magnetic layers
3
and
3
, which are magnetized in the right direction in the drawing (direction perpendicular to a recording medium D; depth direction), and the nonmagnetic electrically-conductive layers
2
and
2
, and the magnetic fields Hbf
1
and Hbf
2
influence the free magnetic layer
1
at the interfaces with the free magnetic layer
1
.
Static magnetic coupling fields (demagnetizing fields) Hd
1
and Hd
2
are also applied into the free magnetic layer
1
from the pinned magnetic layers
3
and
3
.
The sensing electric current
9
mainly flows through the nonmagnetic electrically-conductive layers
2
and
2
having low resistivity, and induction magnetic fields Is
1
and Is
2
by the sensing electric current
9
influence the free magnetic layer
1
.
Additionally, as shown in
FIG. 11
, a lower shield layer
10
is formed on the lower side of the spin-valve type magnetoresistive thin film element at a distance GL
1
from the center of the free magnetic layer
1
of the spin-valve type magnetoresistive thin film element. An upper shield layer
11
is formed on the upper side of the spin-valve type magnetoresistive thin film element at a distance GL
2
from the center of the free magnetic layer
1
. Under the influence of the induction magnetic fields by the sensing electric current
9
, shield bias magnetic fields occur from the lower shield layer
10
and the upper shield layer
11
. A shield bias magnetic field S
1
from the lower shield layer
10
and a shield bias magnetic field S
2
from the upper shield layer
11
influence the free magnetic layer
1
.
Herein, when magnetic fields applied to the free magnetic layer
1
in the right direction in the drawing, that is, interlayer coupling magnetic fields Hbf
1
and Hbf
2
, the induction magnetic field Is
2
, and the shield bias magnetic field S
2
, are assumed to have positive values and when magnetic fields applied to the free magnetic layer
1
in the left direction in the drawing, that is, static magnetic coupling fields Hd
1
and Hd
2
, the induction magnetic field Is
1
, and the shield bias magnetic field S
1
, are assumed to have negative values, if the sum of all the magnetic field values applied to the free magnetic layer
1
is zero, magnetic fields affecting the free magnetic layer
1
are totally offset, enabling satisfactory vertical asymmetry of the regenerated output waveform, which is so-called “asymmetry”.
In the conventional spin-valve type magnetoresistive thin film element, as described above, since laminates disposed on the upper and lower surfaces of the free magnetic layer
1
are perfectly symmetrical, the induction magnetic field Is
1
flowing from the lower laminate into the free magnetic layer
1
, and the induction magnetic field Is
2
flowing from the upper laminates into the free magnetic layer
1
, have the same intensity, and as shown in
FIG. 11
, since induction magnetic fields Is
1
and Is
2
flow into the free m
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Cao Allen T.
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