Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-10-09
2004-12-14
Heinz, A. J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06831817
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic sensor mounted in a hard disk drive or the like for reproduction, and more particularly to a magnetic sensor in which a resistance change rate (&Dgr;R/R) can be improved and magnetization control of a free magnetic layer can be satisfactorily performed.
2. Description of the Related Art
FIG. 26
is a partial sectional view of a structure of a conventional magnetic sensor, looking from a side facing a recording medium.
Numeral
14
shown in
FIG. 26
denotes a barrier layer made of, e.g., Ta. An antiferromagnetic layer
30
made of, e.g., PtMn is formed on the barrier
14
.
A pinned magnetic layer
31
of a magnetic material is formed on the antiferromagnetic layer
30
. A nonmagnetic material layer
32
made of, e.g., Cu is formed on the pinned magnetic layer
31
, and a free magnetic layer
33
is formed on the nonmagnetic material layer
32
. The free magnetic layer
33
is of a multi-layered ferri-structure made up three layers, i.e., magnetic layers
37
,
39
and a nonmagnetic intermediate layer
38
. Note that, in the following description, the magnetic layer
37
on the side contacting the nonmagnetic material layer
32
is called a second magnetic layer and the magnetic layer
39
in an opposing relation to the second magnetic layer
37
with the nonmagnetic intermediate layer
38
interposed therebetween is called a first magnetic layer.
Further, as shown in
FIG. 26
, a barrier layer
7
made of, e.g., Ta is formed on the free magnetic layer
33
.
A hard bias layer
5
is formed on each of both sides of multilayered films from the buffer layer
14
to the barrier layer
7
in the track-width direction (X-direction (positive and negative) shown in FIG.
26
). An electrode layer
8
is formed on the hard bias layer
5
.
In the magnetic sensor having such a structure, magnetization of the pinned magnetic layer
31
is fixed in the height direction (Y-direction shown in
FIG. 26
) by an exchange coupling magnetic field generated between the pinned magnetic layer
31
and the antiferromagnetic layer
30
.
On the other hand, the second magnetic layer
37
and the first magnetic layer
39
both constituting the free magnetic layer
33
are magnetized antiparallel to each other in the track-width direction by a longitudinal bias magnetic field applied from the hard bias layer
5
and the RKKY interaction generated between the second magnetic layer
37
and the first magnetic layer
39
. For example, when the second magnetic layer
37
is magnetized to the right in
FIG. 26
(positive X-direction) in the track-width direction, the first magnetic layer
39
is magnetized to the left in
FIG. 26
(opposed to the positive X-direction) in the track-width direction.
The second magnetic layer
37
and the first magnetic layer
39
both constituting the free magnetic layer
33
are, unlike the pinned magnetic layer
31
, put into a weak single domain state in which magnetization is reversible in response to an external magnetic field. The electrical resistance of the free magnetic layer
33
is changed depending on the relationship between the direction of fixed magnetization of the pinned magnetic layer
31
and the direction of magnetization of the free material layer
33
affected by the external magnetic field. An external signal from a recording medium is reproduced in accordance with a voltage change caused upon a change of the electrical resistance.
When the free magnetic layer
33
is of the multilayered ferri-structure as shown in
FIG. 26
, the layer that actually contributes to the magnetoresistive effect is the second magnetic layer
37
.
Accordingly, when a sensing current flows from the electrode layer
8
primarily to the nonmagnetic material layer
32
, there occurs a shunt loss if the sensing current is shunted to the first magnetic layer
39
, thus resulting in a reduction of the resistance change rate (&Dgr;R/R).
To reduce such a shunt loss, it has been proposed to increase the specific resistance of the first magnetic layer
39
, for example, by adding Cr to the first magnetic layer
39
which has been so far formed of a CoFe alloy or the like. That proposal has, however, invited deterioration of reproduction characteristics, such as lowering of a reproduction output and the occurrence of noises, because the increased specific resistance of the first magnetic layer
39
reduces the coupling magnetic field based on the RKKY interaction generated between the second magnetic layer
37
and the first magnetic layer
39
to such an extent that the second magnetic layer
37
and the first magnetic layer
39
both constituting the free magnetic layer
33
cannot be satisfactorily magnetized in the antiparallel state.
FIG. 27
is a partial sectional view of another conventional magnetic sensor having a different structure, looking from a side facing a recording medium. In
FIG. 27
, the same numerals as those in
FIG. 26
represent the same layers as those in FIG.
26
.
In the magnetic sensor of
FIG. 27
, as with that of
FIG. 26
, a free magnetic layer
33
is of a multi-layered ferri-structure in which a nonmagnetic intermediate layer
38
is interposed between two magnetic layers
37
and
39
. In the structure of
FIG. 27
, however, antiferromagnetic layers
40
are formed on the first magnetic layer
39
of the free magnetic layer
33
with a predetermined spacing left between the antiferromagnetic layers
40
in the track-width direction (X-direction). The method of controlling magnetization of the free magnetic layer
33
using the antiferromagnetic layers
40
, as shown in
FIG. 27
, is called an exchange biasing method.
In the structure of
FIG. 27
, when an exchange coupling magnetic field is generated between the antiferromagnetic layers
40
and both end portions A of the first magnetic layer
39
and magnetization in both the end portions A of the first magnetic layer
39
is fixed, e.g., to the right in
FIG. 27
(positive X-direction) in the track-width direction, magnetization in both end portions A of the second magnetic layer
37
formed in an opposing relation to the first magnetic layer
39
with the nonmagnetic intermediate layer
38
interposed therebetween is fixed to the left in
FIG. 26
(opposed to the positive X-direction) in the track-width direction by a coupling magnetic field based on the RKKY interaction generated between the second magnetic layer
37
and the first magnetic layer
39
.
In a central portion B of the free magnetic layer
33
, the second magnetic layer
37
and the first magnetic layer
39
are also magnetized in the antiparallel state, but they are put into a weak single domain state in which magnetization is reversible in response to an external magnetic field.
That magnetic sensor employing the exchange biasing method also has the problems as with the magnetic sensor of FIG.
26
. Specifically, when the first magnetic layer
39
constituting the free magnetic layer
33
is formed of a CoFe alloy, the resistance change rate (&Dgr;R/R) is reduced with shunting of the sensing current. Further, when the first magnetic layer
39
is formed of a CoFeCr alloy, lowering of the unidirectional exchange bias magnetic field (Hex*) becomes noticeable.
Herein, the term “unidirectional exchange bias magnetic field (Hex*)″ represents a resultant magnetic field of an exchange coupling magnetic field (Hex) primarily generated between the antiferromagnetic layers
40
and the first magnetic layer
39
and a coupling magnetic field based on the RKKY interaction generated between the first magnetic layer
39
and the second magnetic layer
37
.
FIG. 28
is a graph showing the relationship between a film thickness of the first magnetic layer
39
and a unidirectional exchange bias magnetic field (Hex*) resulting when the first magnetic layer
39
is formed of CoFe or CoFeCr
5 at %
in a magnetic sensor having the same multilayered structure as that shown in FIG.
27
.
As seen from
FIG. 28
, when the first magnetic layer
39
is formed of
Hasegawa Naoya
Umetsu Eiji
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Heinz A. J.
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