Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-04-23
2001-10-23
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S125330
Reexamination Certificate
active
06307720
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to thin film magnetic heads provided with a magnetoresistive element and to production processes of the same.
2. Description of the Related Art
Current thin film magnetic heads provided with a magnetoresistive element (MR element) can be classified into anisotropic magnetoresistive (AMR) heads utilizing the anisotropic magnetoresistive effect and giant magnetoresistive (GMR) heads utilizing spin-dependent scattering of the conduction electrons. As an example of such GMR heads, U.S. Pat. No. 5,159,513 discloses a spin valve head having a high magnetoresistive effect in a weak external magnetic field.
FIG. 21
illustrates a schematic configuration is a conventional AMR head. The conventional AMR head comprised of a lower shield layer
7
composed of a magnetic alloy such as sendust (Fe—Al—Si) and a lower gap layer
8
formed on the lower shield layer
7
. Onto the lower gap layer
8
is laminated an AMR element layer
10
. The AMR layer
10
is comprised of a soft magnetic layer
11
, a nonmagnetic conductive layer
12
formed on the layer
11
, and a ferromagnetic layer (AMR material layer)
13
formed on the layer
12
. On both sides of the AMR element layer
10
are formed permanent magnet layers
15
, and lead layers
16
in this order.
Onto these layers are formed an upper gap layer
18
and a upper shield layer
19
in this order.
For optimum operations of such an AMR head, two bias magnetic fields are required to apply to the ferromagnetic layer
13
which exhibits the AMR effect.
A first bias magnetic field is to ensure resistance changes of the ferromagnetic layer
13
to respond linearly to a magnetic flux from a magnetic medium. The first bias magnetic field is applied in perpendicular direction (Z direction in
FIG. 21
) to the film plane of the magnetic medium and in parallel with the plane of the ferromagnetic layer
13
. The first bias magnetic filed is generally called as “lateral bias”, where a sensing current is passed from the lead layer
16
to the AMR element layer
10
to produce a current magnetic field and thereby to magnetize the soft magnetic layer
11
in the Z direction, and a lateral bias is thus applied onto the ferromagnetic layer
13
in the Z direction by the magnetization of the soft magnetic filed.
The second bias magnetic filed is generally called as “longitudinal bias”, which is applied in parallel with the planes of the magnetic medium and the ferromagnetic layer
13
(X direction in FIG.
21
). The longitudinal bias magnetic field is to reduce Barkhausen noises generated by a plenty of magnetic domains formed in the ferromagnetic layer
13
, in other words, to smooth resistance changes from the magnetic medium to this magnetic flux with less noises.
Reduction of the Barkhausen noises requires the ferromagnetic layer
13
to be put into a single magnetic domain state. Methods of applying longitudinal bias to this end generally include two techniques, i.e., a technique of providing the permanent magnet layers
15
,
15
on both sides of the ferromagnetic layer
13
to utilize a leakage flux from the permanent magnet layers
15
; and another technique of utilizing an exchange anisotropic magnetic field generated on a contact boundary surface between an antiferromagnetic layer and a ferromagnetic layer.
As a structure of GMR heads utilizing the exchange coupling by an antiferromagnetic layer is known a spin-valve type head illustrated in FIG.
22
.
The GMR head illustrated in
FIG. 22
differs from the AMR head illustrated in
FIG. 21
in that the former comprises a GMR element layer
20
instead of the AMR element layer
10
.
The GMR element layer is comprised of a free magnetic layer
22
, a nonmagnetic conductive intermediate layer
23
, a pinned magnetic layer
24
and an antiferromagnetic layer
25
.
In the configuration shown in
FIG. 22
, bias in the track direction (X direction in
FIG. 22
) should be applied onto the free magnetic layer
22
by the permanent magnet layers
15
,
15
to ensure that the free magnetic layer
22
has the magnetization oriented in the track direction in a single magnetic domain state, and the pinned magnetic layer
24
should have the magnetization oriented in the Z direction in
FIG. 22
, in a single magnetic domain state by applying bias in the Z direction, i.e., the direction perpendicular to the magnetization of the free magnetic layer
22
. In other words, the magnetization of the pinned magnetic layer
24
should not be changed by a flux from a magnetic medium (in the Z direction in FIG.
22
), and the magnetization of the free magnetic layer
22
should rotate in the range of 90±&thgr;° with respect to the magnetization of the pinned magnetic layer
24
to give linear responsivity of the magnetoresistive effect.
A comparatively large bias magnetic field is required to fix the magnetization of the pinned magnetic layer
24
in the Z direction in
FIG. 22
, and the larger is this bias magnetic field, the better is the fixation done. At least a 100-Oe bias magnetic field is required to overcome an antimagnetic field in the Z direction in FIG.
22
and to inhibit the magnetization from rotating or fluctuating by a flux from a magnetic medium. To obtain the bias magnetic field, the configuration illustrated in
FIG. 22
utilizes an exchange anisotropic magnetic field generated by providing the antiferromagnetic layer
25
in contact with the pinned magnetic layer
24
.
In such a configuration as shown in
FIG. 22
, the exchange coupling formed by providing the antiferromagnetic layer
25
in contact with the pinned magnetic layer
24
allows the pinned magnetic layer
24
to have the magnetization oriented and fixed in the Z direction. When a leakage magnetic field from a magnetic medium transferring in the Y direction is applied, the electrical resistance of the GMR element layer
20
changes with changes of the magnetization of the free magnetic layer
22
, and hence the leakage magnetic field of the magnetic medium can be detected through the electrical resistance changes.
The bias applied to the free magnetic layer
22
is to ensure the linear responsivity and to reduce Barkhausen noises generated due to the formation of a number of magnetic domains, and applied in a similar manner in the longitudinal bias in the AMR head. In the configuration shown in
FIG. 22
, permanent magnet layers
15
,
15
are provided on both sides of the free magnetic layer
22
and a leakage flux from the permanent magnet layers
15
,
15
is used as the bias.
During operation of such a thin film magnetic head, the vicinity of an MR element layer such as an AMR element layer or a GMR element layer is known to rise in temperature readily up to about 120° C. due to heat generated through a stationary sensing current. At such a high temperature, the electrical resistance of a ferromagnetic layer changes due to a high sensitivity of the MR element to temperature changes, and hence the reading signals are disturbed. In the GMR elements, the exchange anisotropic magnetic field by the antiferromagnetic layer
25
composed of, for example, FeMn is highly sensitive to changes in temperature, and decreases almost linearly with respect to the temperature and disappears at about 150° C. (blocking temperature: Tb), so that a stable exchange anisotropic magnetic field cannot be obtained.
To solve these problems, conventional thin film magnetic heads provide upper and lower gap layers
8
,
18
made of aluminium oxide (Al
2
O
3
) with respect to the AMR element layer
10
or the GMR element layer
20
to dissipate the heat gradually through the gap layers
8
,
18
to the shield layers
7
,
19
to thereby dissipate it to outside.
Demands have been made to enhance the output of thin film magnetic heads, and to this end, a stationary sensing current density applied to the MR element layer should be increased by making the thickness or depth of the MR element thinner.
In conventional thin film magnetic heads, however, when a stationary sensing curren
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Cao Allen
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