Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-12-20
2002-10-01
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S125330
Reexamination Certificate
active
06459551
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin magnetic head provided with a magnetoresistive element.
2. Description of the Related Art
Conventional thin film magnetic heads provided with a magnetoresistive element (MR element) known in the art include an anisotropic magnetoresistive head (AMR head) making use of-anisotropic magnetoresistive effect and a giant megnetoresistive (GMR) head making use of spin-dependent scattering of conduction electrons. A spin-valve magnetic head that exhibits a high magnetoresistive effect in a low external magnetic field is disclosed in the specification of U.S. Pat. No. 5,159,513 as one embodiment of the GMR head.
FIG. 23
illustrates the construction of the conventional AMR head. The conventional AMR head comprises a lower gap layer
8
formed on a lower shield layer
7
comprising a magnetic alloy such as Sendust (a Fe—Al—Si alloy). An AMR element layer
10
is laminated on this lower gap layer
8
. This AMR element layer
10
is formed by depositing a non-magnetic layer
12
on a soft magnetic layer
11
followed by depositing a ferromagnetic layer (AMR feedstock layer)
13
on the non-magnetic layer
12
. Magnetic layers
15
are provided at both sides of the AMR element layer
10
, and conductive layers
16
are additionally provided on the magnetic layer
10
.
An upper gap layer
18
is further formed on the conductive layers
16
and AMR element layer
10
, and an upper shield layer
19
is further formed on the upper gap layer
18
.
The ferromagnetic layer
13
that exhibits the AMR effect has been regarded to require two bias electric fields for optimum operation of this sort of the AMR head.
The first bias magnetic field is applied along the direction perpendicular to one face of a magnetic medium (the Z-direction in
FIG. 23
) and parallel to the face of the ferromagnetic layer
13
, in order to allow resistance changes of the ferromagnetic layer
13
to linearly respond against the magnetic flux from the magnetic medium. This first bias magnetic field is usually termed a transverse bias, which allows the soft magnetic layer
11
to be magnetized along the Z-direction by a magnetic field generated by flowing a sensing current from the conductive layer
16
to the AMR element layer
10
. Magnetization of the soft magnetic layer
11
endows the ferromagnetic layer
13
with a transverse bias along the Z-direction.
The second bias magnetic field is usually termed a vertical bias, which is applied parallel to the magnetic medium and film face of the ferromagnetic layer
13
(the X-direction in FIG.
1
). The vertical bias magnetic field is applied in order to suppress Barkhausen noises generated by forming a number of magnetic domains in the ferromagnetic layer
13
or, in other words, to obtain a smooth resistance change with few noises against the magnetic flux from the magnetic medium.
The ferromagnetic layer
13
should be made to be a single magnetic domain for suppressing the Barkhausen noise described above. The vertical bias is usually applied by two methods for suppressing the Barkhausen noise. The first method comprise using a leak magnetic flux from the magnetic layer
15
by disposing two magnetic layers
15
and
15
at both sides of the ferromagnetic layer
13
, while the second method comprises using an exchange anisotropic magnetic field generated at the contact-interface between an antiferromagnetic layer and ferromagnetic layer.
FIG. 24
shows the construction of a spin-valve type GMR head making use of the exchange anisotropic coupling of the antiferromagnetic layer.
The GMR head shown in
FIG. 24
differs from the AMR head shown in
FIG. 23
in that a GMR element layer
20
is provided instead of the AMR element layer
10
.
The GMR element layer
20
is composed of a free ferromagnetic layer
22
, non-magnetic intermediate layer
23
, pinned ferromagnetic layer
24
and antiferromagnetic layer
25
.
In accordance with the structure shown in
FIG. 24
, magnetization should be aligned toward the track direction while allowing the free ferromagnetic layer
22
to form a single magnetic domain by applying a bias along the track direction (X-direction in
FIG. 24
) using the magnetic layers
15
and
15
, as well as aligning the magnetization of the pinned ferromagnetic layer
24
toward the Z-direction in
FIG. 24
, or along the Z-direction in
FIG. 24
while allowing the pinned ferromagnetic layer
24
to form a single magnetic domain by applying a bias along the direction perpendicular to the magnetization of the free ferromagnetic layer
22
. In other words, the direction of magnetization of the pinned ferromagnetic layer
24
should not be changed by the magnetic flux (Z-direction in FIG.
24
). Rather, the linear response of the magnetoresistive effect is obtained by allowing the direction of the free ferromagnetic layer
22
to change within a rage of 90° ±&thgr;° relative to the direction of magnetization of the pinned ferromagnetic layer
24
.
Relatively a large bias magnetic field is required for fixing the direction of magnetization of the pinned ferromagnetic layer
24
along the Z-direction. The larger the bias magnetic field is, the better pinning effect is obtained. At least 100 Oe of the bias magnetic field is required for surmounting the anti-magnetic field along the Z-direction in FIG.
24
and for preventing fluctuation of the direction of magnetic field due to the magnetic flux from the magnetic medium. The method for obtaining such bias magnetic field as described above comprises to take advantage of the exchange anisotropic magnetic field generated by providing the antiferromagnetic layer
25
in close contact to the pinned ferromagnetic layer
24
.
In the structure as shown in
FIG. 24
, magnetization of the ferromagnetic layer
24
is fixed along the Z-direction by the exchange anisotropic coupling generated by providing the antiferromagnetic layer
25
in close contact to the pinned ferromagnetic layer
24
. Therefore, the electric resistance of the GMR element layer
20
is changed by changing the direction of magnetization of the free ferromagnetic layer
22
when a leak magnetic field from the magnetic medium traveling along the Y-direction is applied, thus enabling the leak magnetic field from the magnetic medium to be sensed by this resistance change.
The bias magnetic field is applied to the free ferromagnetic layer
22
for the purposes of securing linear responses and suppressing the Barkhausen noise generated by forming many magnetic domains. The bias is applied by the same method as in the vertical vias in the AMR head or, in other words, the leak magnetic flux from the magnetic layer
15
is utilized as the bias by providing the magnetic layers
15
at both sides of the free ferromagnetic layer
22
in the construction as shown in FIG.
24
.
It is known in the art that the temperature in the vicinity of the MR element layer such as the AMR element layer and GMR element layer is readily increased up to 120° C. due to the heat caused by the stationary sensing current during operation of the thin film magnetic head. The MR element is so sensitive to temperature changes that electric resistance of the ferromagnetic layer is changed due to temperature increase of the MR element layer by the heat generated as described above, causing disturbance of read signals. Moreover, the exchange anisotropic magnetic field generated by the antiferromagnetic layer comprising FeMn and the like is also very sensitive to temperature changes in the GMR element, and the exchange anisotropic magnetic field nearly linearly decays -against the temperature before it is extinguished at about 150° C. (blocking temperature: Tb). Therefore, a stable exchange anisotropic magnetic field can not be obtained due to the problems as described above.
The conventional thin film magnetic head for solving the problems as hitherto described comprises upper and lower gap layers
8
and
18
made of alumina (Al
2
O
3
) in the AMR element layer
10
or GMR element layer
20
.
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Castro Angel
Hudspeth David
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