Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-07-30
2001-09-18
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06292334
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a MR (magnetoresistive)/inductive combined thin film magnetic head loaded on, for example, a hard disk device, and particularly to a thin film magnetic head comprising a shield layer having a magnetic domain structure stabilized for obtaining stable reproduced signal waveforms in an MR element.
2. Description of the Related Art
FIG. 3
is an enlarged sectional view showing a conventional thin film magnetic head as viewed from the ABS (air bearing surface) side opposite to a recording medium.
This thin film magnetic head is a so-called MR/inductive combined thin film magnetic head comprising a reading head h
1
using a magnetoresistive effect and a writing inductive head h
2
, both of which are laminated at the trailing-side end of a slider, which constitutes, for example, a floating type head.
In the reading head h
1
, a lower gap layer
2
made of a nonmagnetic material such as Al
2
O
3
(alumina) or the like is formed on a lower shield layer
1
made of sendust or a NiFe alloy (permalloy), and a magnetoresistive element layer
3
is formed on the lower gap layer
2
. The magnetoresistive element layer
3
comprises a spin valve film {a GMR (Giant Magnetoresistive) element} having, for example, an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic electrically conductive layer, and a free magnetic layer. In the spin valve film, magnetization of the pinned magnetic layer is fixed in the direction perpendicular to the drawing (the depth direction), and magnetization of the free magnetic layer is arranged in the direction of the track width. When a magnetic field enters from a recording medium in the direction perpendicular to the drawing, magnetization of the free magnetic layer is changed to change electric resistance by the relation between fixed magnetization of the pinned magnetic layer and variable magnetization of the free magnetic layer, reproducing a record magnetic field.
Hard magnetic bias layers
4
are formed as longitudinal bias layers on both sides of the magnetoresistive element layer
3
. On the hard magnetic bias layers
4
are respectively formed electrode layers
5
made of a nonmagnetic electrically conductive material having low electric resistance, such as Cu (copper), W (tungsten), or the like. An upper gap layer
6
made of a nonmagnetic material such as alumina is further formed on the electrode layers
5
.
An upper shield layer
7
is formed on the upper gap layer
6
by plating permalloy or the like so that gap length G
11
is determined by the distance between the lower shield layer
1
and the upper shield layer
7
. In the inductive head h
2
, the upper shield layer
7
functions as a leading-side core (lower core layer) for applying a record magnetic field to the recording medium.
A gap layer (nonmagnetic material layer)
9
made of alumina or the like, and an insulation layer (not shown) made of polyimide or a resist material are laminated on the lower core layer
7
, and a coil layer
10
formed in a helical pattern is provided on the insulation layer. The coil layer
10
is made of a nonmagnetic electrically conductive material having low electric resistance, such as Cu (copper) or the like. The coil layer
10
is also surrounded by the insulation layer (not shown) made of polyimide or a resist material, and an upper core layer
11
is formed on the insulation layer by using a magnetic material such as permalloy or the like. The upper core layer
11
functions as the trailing-side core of the inductive head h
2
for supplying a recording magnetic field to the recording medium.
As shown in
FIG. 3
, the upper core layer
11
is opposite to the lower core layer
7
with the gap layer
9
held therebetween on the side opposite to the recording medium to form a magnetic gap with a magnetic gap length G
12
for supplying a recording magnetic field to the recording medium. Further, a protective layer
12
made of alumina or the like is provided on the upper core layer
11
.
In the inductive head h
2
, a recording current is supplied to the coil layer
10
to supply a recording magnetic field to the upper core layer
11
and the lower core layer
7
from the coil layer
10
. As a result, a magnetic signal is recorded on the recording medium such as a hard disk or the like by a leakage magnetic field from the magnetic gap between the lower core layer
7
and the upper core layer
11
.
In order to improve stability of signals output from the magnetoresistive layer
3
, it is necessary to decrease an inflow of external noise into the magnetoresistive element layer
3
. Therefore, it is thought to be necessary that a magnetic field is applied in the direction of the track width during the deposition of the shield layers
1
and
7
or in treatment after the deposition to arrange the uniaxial anisotropic direction of the lower shield layer
1
and the upper shield layer
7
in the direction of the track width so that the direction of the track width becomes the easy axis of magnetization, and the direction (the direction perpendicular to the drawing) perpendicular to the magnetic medium becomes the hard axis of magnetization, thereby preventing magnetization of the shield layers
1
and
7
from adversely affecting the magnetoresistive element layer
3
.
However, when each of the lower shield layer
1
and the upper shield layer
7
comprises a single layer made of an NiFe alloy (permalloy), as shown in
FIG. 3
, the application of a magnetic field in the direction of the track width brings the domain structure of the shield layers
1
and
7
into a multiple magnetic domain state, creating a state wherein magnetic anisotropy is dispersed, as shown in FIG.
4
.
Particularly, in the vicinity of the ends of the shield layers
1
and
7
, the direction of magnetization is shifted from the direction of the track width, as shown in magnetic domains
13
, or perpendicular to the direction of the track width, as shown in magnetic domains
14
. As a result of examination of the anisotropic direction in a wafer in the head manufacturing process, in the shield layers
1
and
7
shown in
FIG. 4
, the variation of the magnetization direction (variation in skew angle) is as large as about ±10°.
The variation in skew angle represents the angle of deviation of magnetization from the direction of the track width. As the variation in skew angle increases, the magnetic reversibility of the shield layers
1
and
7
deteriorates to deteriorate the shield function, and the magnetoresistive element layer
3
held between the shield layers
1
and
7
is affected by the variation of magnetization of the shield layers
1
and
7
. For example, when the magnetoresistive element layer
3
comprises a spin valve film, the magnetic domain of the free magnetic layer in the spin valve film, in which magnetization to be arranged in the direction of the track width, is made unstable, thereby causing Barkhausen noise. Particularly, the effect on the magnetoresistive element layer
3
significantly occurs as the gap length G
11
shown in
FIG. 3
decreases due to an increase in recording density.
A method of decreasing the variation of skew angle is to improve the magnetic material which constitutes the shield layers
1
and
7
. As described above, the shield layers
1
and
7
shown in
FIG. 7
are made of an NiFe alloy which exhibits an anisotropic magnetic field Hk of as low as about 2 to 4 (Oe), and thus the magnetic domain structure of the shield layers
1
and
7
made of the NiFe alloy is readily made unstable, thereby increasing the variation in skew angle. Therefore, by using a material having a higher anisotropic magnetic field Hk than the NiFe alloy, for example, a CoZrNb alloy (Hk=about 7 to 12 Oe), for the shield layers
1
and
7
, the variation in skew angle of the shield layers
1
and
7
can be decreased.
FIG. 5
is a plan view showing the magnetic domain structure of shield layers
1
and
7
made of a magnetic material having a high anisotropi
Hasegawa Naoya
Koike Fumihito
Sato Kiyoshi
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Evans Jefferson
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