Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-01-25
2003-07-15
Klimowicz, William (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324110, C360S324120
Reexamination Certificate
active
06594121
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thin-film magnetic heads provided with magnetoresistive thin-film elements in which the resistance changes greatly in response to changes in external magnetic fields, and more particularly, to a technique using a structure in which a longitudinal bias magnetic field is satisfactorily applied to a free magnetic layer.
2. Description of the Related Art
A giant magnetoresistive (GMR) head utilizing an element having a giant magnetoresistive effect (GMR effect) has been known as a magnetoresistive read head for reading magnetic data from a magnetic recording medium such as a hard disk. A spin-valve type head has been known as a GMR head having a relatively simple structure and a high rate of resistance change in relation to an external magnetic field.
FIG. 20
is a sectional view of an example of a structure of such a spin-valve type GMR thin-film element.
The structure shown in
FIG. 20
includes a laminate
207
, that is trapezoidal in section, in which an underlying layer
201
, a free magnetic layer
202
, a nonmagnetic conductive layer
203
, a pinned magnetic layer
204
, an antiferromagnetic layer
205
, and a protective layer
206
are deposited on a substrate in that order. Hard bias layers
208
and conductive layers
209
are formed so as to cover the inclined sides of the laminate
207
.
In the structure shown in
FIG. 20
, the pinned magnetic layer
204
has a higher coercive force than that of the free magnetic layer
202
, and the pinned magnetic layer
204
is aligned in a single-domain state in the Y direction in
FIG. 20
by an exchange anisotropic magnetic field caused by the antiferromagnetic layer
205
deposited directly on the pinned magnetic layer
204
, and the magnetization direction is fixed in the Y direction.
The hard bias layers
208
are magnetized in the X
1
direction in
FIG. 20
, and since the free magnetic layer
202
adjacent to the hard bias layers
208
is aligned in a single-domain state in the X
1
direction by the hard bias layers
208
, Barkhausen noise, which is generated by the formation of many magnetic domains in the free magnetic layer
202
, is prevented from occurring.
In this structure, a sensing current is applied from the conductive layer
209
to the free magnetic layer
202
, the nonmagnetic conductive layer
203
, and the pinned magnetic layer
204
. The driving direction of a magnetic recording medium such as a hard disk is set in the Z direction in
FIG. 20
, and when a fringing magnetic field from the recording medium is applied in the Y direction, the magnetization of the free magnetic layer
202
changes from the X
1
direction to the Y direction. Because of the relationship between the change in the magnetization direction in the free magnetic layer
202
and the fixed magnetization direction of the pinned magnetic layer
204
, the electrical resistance changes, and the fringing magnetic field from the recording medium is detected by a voltage change based on the change in the electrical resistance.
FIG. 21
shows an example of another structure of a spin-valve type element, in which a bias is applied in a manner different from that in the structure shown in FIG.
20
. The structure shown in
FIG. 21
includes a laminate
217
in which an underlying layer
211
composed of Ta, a free magnetic layer
212
composed of an NiFe alloy, a nonmagnetic conductive layer
213
composed of Cu, a pinned magnetic layer
214
composed of an NiFe alloy, an antiferromagnetic layer
215
composed of an FeMn alloy, and a protective layer
216
composed of an insulating material are deposited on a substrate
210
in that order. On both sides of the laminate
217
, ferromagnetic layers
218
composed of an NiFe alloy, antiferromagnetic layers
219
composed of an NiMn alloy, and conductive layers
220
composed of Cu are deposited.
In the structure shown in
FIG. 21
, the pinned magnetic layer
214
is aligned in a single-domain state in the direction represented by an arrow
222
(in the Y direction) by an exchange anisotropic magnetic field caused by the antiferromagnetic layer
215
deposited on the pinned magnetic layer
214
, and the magnetization direction is fixed in the Y direction. The antiferromagnetic layer
219
composed of the NiMn alloy is not antiferromagnetic at room temperature. However, when heated, the antiferromagnetic layer
219
becomes antiferromagnetic, and by applying a magnetic field in the direction represented by an arrow
221
(in the X
1
direction) in
FIG. 21
during heat treatment, the magnetization is aligned along the direction of the applied magnetic field. After the heat treatment, the magnetization of the antiferromagnetic layer
219
is fixed, generating an antiferromagnetic coupling with the ferromagnetic layer
218
, and the free magnetic layer
212
can be aligned in a single-domain state in the magnetization direction of the ferromagnetic layer
218
also in the structure shown in FIG.
21
. Thus, the magnetoresistive effect can be obtained without causing Barkhausen noise.
With respect to the structure shown in
FIG. 20
, in which the free magnetic layer
202
is aligned in a single-domain state by the hard bias layers
208
, ends of the free magnetic layer
202
tend to become insensitive zones in which the magnetization direction does not easily change under the influence of the magnetization direction of the hard bias layers
208
, resulting in a hindrance to the narrowing of tracks associated with the improvement in the recording density of magnetic recording media.
Therefore, in view of the narrowing of tracks, the biasing method shown in
FIG. 21
, in which no hard bias layer is used, could be effective. However, the application of a bias in the structure shown in
FIG. 21
gives rise to the following problems.
In the structure shown in
FIG. 21
, the antiferromagnetic layer
215
pins the magnetization direction of the pinned magnetic layer
214
, and the antiferromagnetic layer
219
aligns the free magnetic layer
212
in a single-domain state for biasing. The magnetization directions caused by the antiferromagnetic layer
215
and the antiferromagnetic layer
219
differ by 90°.
Although the magnetization directions of the antiferromagnetic layers
215
and
219
are usually controlled by deposition in a magnetic field or magnetic annealing after deposition, it is very difficult to align the magnetization of the antiferromagnetic layer
219
, which is formed later, in a direction different from that of the magnetization of the antiferromagnetic layer
215
, which is formed first, without disturbing the magnetization direction of the antiferromagnetic layer
215
.
As described in the specification of Japanese Unexamined Patent Publication No. 8-45032 (Japanese Patent Application No. 7-122104) which discloses the structure shown in
FIG. 21
, the aforementioned problem can be avoided by a method in which, using a magnetic film of an FeMn alloy and a magnetic film of an NiMn alloy having different Néel temperatures, the magnetic film having a higher Néel temperature is firstly subjected to high-temperature heat treatment for aligning the magnetic field, and secondly the magnetic film having a lower Néel temperature is subjected to low-temperature heat treatment for aligning the magnetic field in the direction different from that in the first heat treatment by 90°. However, since the FeMn alloy constituting an antiferromagnetic layer has a low Néel temperature and has a low blocking temperature at which antiferromagnetism is believed to disappear, a bias magnetic field caused by the antiferromagnetic layer made of the FeMn alloy easily becomes unstable due to heat generated when a magnetic recording device such as a hard disk drive is operated.
Furthermore, in the structure disclosed in Japanese Unexamined Patent Publication No. 8-45032, an NiMn alloy film having a high Néel temperature which requires heat treatment is used for applying a longitudinal bias, and an FeMn alloy film having a low Néel temper
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Klimowicz William
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