Metal treatment – Process of modifying or maintaining internal physical... – Magnetic materials
Reexamination Certificate
1999-11-05
2002-04-02
Sheehan, John (Department: 1742)
Metal treatment
Process of modifying or maintaining internal physical...
Magnetic materials
C029S603080
Reexamination Certificate
active
06364961
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to magnetic heads and more particularly to an improvement of a GMR (giant magneto-resistance) head having a so-called spin-valve structure.
A GMR head is a high-sensitivity magnetic head that detects a change of resistance of a magnetic layer that in turn occurs in response to a change of direction of a very weak external magnetic field. Because of the high magnetic sensitivity, a GMR head is expected to play a major role in a high-density magnetic recording apparatus as a high-resolution and high-sensitivity magnetic head.
FIG. 1
shows the overall construction of a magnetic head
10
having a typical conventional spin-valve structure, while
FIG. 2
shows the construction of a spin-valve head
14
used in the magnetic head of FIG.
1
.
Referring to
FIG. 1
, the magnetic head
10
includes a lower magnetic shield layer
12
of a magnetic material such as FeNi, CoFe or FeN provided on a substrate
11
of Al
2
TiC. On the foregoing lower magnetic shield layer
12
, there is provided a spacer layer
13
of a non-magnetic material such as Al
2
O
3
, and a magnetic sensor
14
having a spin-valve structure is formed on the spacer layer
13
.
The magnetic sensor
14
is covered by another spacer layer
15
also of a non-magnetic material similar to the spacer layer
13
, and an upper magnetic shield layer
16
of a soft magnetic material such as FeNi or CoFe is provided on the spacer layer
15
. Thereby, the spacer layer
13
, the magnetic sensor
14
and the spacer layer
15
form together a minute magnetic read gap between the upper and lower magnetic shield layers
12
and
16
with a size of about 200 nm.
On the upper magnetic shield layer
16
, there is provided another spacer layer
17
of a non-magnetic material with a thickness of about 350 nm, and a coil pattern
19
is provided on the spacer layer
17
with an intervening insulation layer
18
, wherein the insulation layer
18
continuously has a reducing thickness toward a front end
10
A of the magnetic head
10
. The coil pattern
19
is covered by another insulation layer
20
, and a magnetic pole
21
of a magnetic material such as FeNi or CoFe is provided on the foregoing another insulation layer
20
such that the thickness of the insulation layer
20
decreases continuously toward the foregoing front end
10
A of the magnetic head
10
. As a result of the decreasing thickness of the insulation layers
18
and
20
at the front end
10
A of the magnetic head
10
, the magnetic pole
21
makes direct contact with the spacer layer
17
at the front end is formed
10
A. There a minute magnetic write gap is formed between the upper magnetic shield
16
and the magnetic pole
21
. It should be noted that the upper magnetic shield
16
extends to the magnetic pole
21
at a part not illustrated in
FIG. 1 and a
magnetic circuit is formed.
The magnetic head
10
scans the surface of a magnetic recording medium such as a magnetic disk at the foregoing front edge surface
10
A, and the magnetic sensor
14
detects the magnetization recorded on the surface of the magnetic recording medium at the foregoing magnetic read gap. Further, a recording of information is made on the magnetic recording medium at the foregoing write gap by energizing the coil
19
by an information signal.
FIG. 2
shows the construction of the magnetic sensor
14
in detail, wherein those parts explained already with reference to
FIG. 1
are designated by the same reference numerals and the description thereof will be omitted.
Referring to
FIG. 2
, the magnetic sensor
14
includes a magnetic detection layer or so-called “free layer”
14
A of a soft magnetic material such as CoFe or NiFe formed on the spacer layer
14
, wherein the free layer changes the direction of magnetization freely in response to the magnetization of the magnetic recording medium.
On the free layer
14
A, there is provided an intermediate layer
14
B of a non-magnetic material such as Cu, and a fixed magnetization layer or so-called “pinned layer”
14
C is provided on the intermediate layer
14
B with a predetermined fixed magnetization, wherein the pinned layer
14
C is formed of a soft magnetic material such as CoFe or NiFe similarly to the free layer
14
B. It should be noted that the magnetization of the pinned-layer
14
C is fixed in the direction of magnetization of a magnetization-fixing layer or so-called “pinning layer”
14
D, wherein the pinning layer
14
D is formed of an anti-ferromagnetic material such as FeMn or PdPtMn and provided on the pinned layer
14
C. It should be noted that the pinning layer
14
D fixes the magnetization of the pinned layer
14
C by spin-exchange interaction. Thereby, the magnetization of the magnetic recording medium is detected by detecting a change of electric resistance that occurs in response to the change of direction of magnetization in the free layer
14
A with respect to the direction of magnetization in the pinned layer
14
C. In
FIGS. 1 and 2
, it should be noted that the electrodes for detecting the foregoing resistance change is omitted from illustration. Further, it should be noted that the pinning layer
14
D, lacking a spontaneous magnetization, is relatively immune to the external magnetic field.
In the magnetic sensor
14
having such a construction, in which the direction of magnetization of the free layer
14
A changes in response to the direction of magnetization of the magnetic recording medium; it should be noted that the resistance of the magnetic sensor
14
becomes minimum when the direction of magnetization of the layer
14
A is parallel to the direction of the magnetization of the pinned layer
14
C. When the direction of magnetization of the layer
14
A is in an anti-parallel relationship with the direction of magnetization of the pinned layer
14
C, on the other hand, the resistance of the magnetic sensor
14
becomes maximum.
In the case of using the magnetic sensor
14
for the magnetic head
10
, it is advantageous to set the direction of magnetization of the pinned layer
14
C perpendicular to the direction of magnetization of the free layer
14
A in a free state in which there is no external magnetic field applied to the magnetic sensor
14
. See FIG.
3
A. By doing so, the resistance of the magnetic sensor
14
is increased or decreased generally symmetrically depending on whether the magnetization of the magnetic recording medium is parallel or anti-parallel to the magnetization of the pinned layer
14
C, as indicated in FIG.
3
B. Such a generally symmetric increase and decrease of the resistance facilitates the signal processing in the magnetic recording and reproducing apparatus.
It should be noted that the control of magnetization of a magnetic body is conducted in a heat treatment process.
FIG. 4
shows a heat treatment process conducted conventionally in the process of forming the spin-valve structure of FIG.
2
.
Referring to
FIG. 4
, the spin valve structure of
FIG. 2
is formed in a step
1
of
FIG. 4
by depositing the layers
14
A-
14
D under the existence of an initial magnetic field with a predetermined initial direction designated as a 0° direction. The free layer
14
A thus formed has an easy axis of magnetization in the foregoing 0° direction.
Next, in the step
2
of
FIG. 4
, the spin-valve structure of
FIG. 2
is subjected to a thermal annealing process to a temperature close to a blocking temperature of the pinning layer
14
D, and a magnetic field is applied in the foregoing 0° direction as indicated by blank arrows. As a result, the direction of magnetization of the pinned layer
14
C is aligned in the 0° direction.
FIGS. 5A and 5B
explain the blocking temperature.
In a magnetic system in which an anti-ferromagnetic layer and a soft magnetic layer form an exchange coupling as in the case of the spin-valve structure of
FIG. 2
, it should be noted that the hysteresis curve of the magnetic system is displaced along the horizontal axis representing the magnetic field H by an amount Hua as indicated in
FIG. 5
Kishi Hitoshi
Nagasaka Keiichi
Shimizu Yutaka
Tanaka Atsushi
Greer Burns & Crain Ltd.
Sheehan John
LandOfFree
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