Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-11-19
2004-07-06
Watko, Julie Anne (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06760200
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spin-valve thin-film magnetic element in which electrical resistance changes due to the relationship between the pinned magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer which is influenced by an external magnetic field, and to a thin-film magnetic head provided with the spin-valve thin-film magnetic element. More particularly, the invention relates to a technique which improves the output and stability of the element, which reduces Barkhausen noise, etc., and which allows satisfactory alignment of the domain of the free magnetic layer when the track width is narrowed.
2. Description of the Related Art
A spin-valve thin-film magnetic element is one type of giant magnetoresistive (GMR) element exhibiting a giant magnetoresistance effect, and it detects a recorded magnetic field from a magnetic recording medium, such as a hard disk.
The spin-valve thin-film magnetic element has a relatively simple structure among GMR elements, and has a high rate of resistance change relative to an external magnetic field, and the resistance changes in response to a weak magnetic field.
FIG. 35
is a sectional view of a conventional spin-valve thin-film magnetic element, viewed from a surface facing a recording medium (air bearing surface; ABS).
The spin-valve thin-film magnetic element shown in
FIG. 35
is a so-called bottom-type single spin-valve thin-film magnetic element in which an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic conductive layer, and a free magnetic layer, one each, are formed.
For the spin-valve thin-film magnetic element, a magnetic recording medium, such as a hard disk, travels in the Z direction in the drawing, and a fringing magnetic field from the magnetic recording medium is directed in the Y direction.
As shown in
FIG. 35
, the conventional spin-valve thin-film magnetic element includes a laminate
109
in which an underlayer
106
, an antiferromagnetic layer
101
, a pinned magnetic layer
102
, a nonmagnetic conductive layer
103
, a free magnetic layer
104
, and a protective layer
107
are deposited in that order on a substrate; hard bias layers
105
formed at both sides of the laminate
109
; and electrode layers
108
formed on the hard bias layers
105
. The underlayer
106
is composed of tantalum (Ta) or the like, and the antiferromagnetic layer
101
is composed of an NiO alloy, an FeMn alloy, an NiMn alloy, or the like. The pinned magnetic layer
102
and the free magnetic layer
104
, respectively, are composed of Co, an NiFe alloy, or the like. The nonmagnetic conductive layer
103
is composed of a copper (Cu) film, the hard bias layers
105
are composed of a cobalt-platinum (Co—Pt) alloy or the like, and the electrode layers
108
are composed of Ta, Au, Cr, W, or the like.
Since the pinned magnetic layer
102
is brought into contact with the antiferromagnetic layer
101
, an exchange coupling magnetic field (exchange anisotropic magnetic field) is generated at the interface between the pinned magnetic layer
102
and the antiferromagnetic layer
101
, and the magnetization direction of the pinned magnetic layer
102
is pinned, for example, in the Y direction.
Since the hard bias layers
105
are magnetized in the X1 direction in the drawing, the variable magnetization of the free magnetic layer
104
sandwiched between the hard bias layers
105
is aligned in the X1 direction. Thereby, the variable magnetization of the free magnetic layer
104
and the pinned magnetization of the pinned magnetic layer
102
are substantially orthogonal to each other.
In the spin-valve thin-film magnetic element, a sensing current is applied from one electrode layer
108
formed on one hard bias layer
105
to the pinned magnetic layer
102
, the nonmagnetic conductive layer
103
, and the free magnetic layer
104
. A magnetic recording medium, such as a hard disk, travels in the Z direction in the drawing, and when a fringing magnetic field from the magnetic recording medium is applied in the Y direction, the magnetization direction of the free magnetic layer
104
is rotated from the X1 direction to the Y direction. At this stage, electrical resistance changes due to the relationship between the varied magnetization direction of the free magnetic layer
104
and the pinned magnetization direction of the pinned magnetic layer
102
, which is referred to as the magnetoresistance (MR) effect, and the fringing magnetic field from the magnetic recording medium is detected by a voltage change based on the change in the electrical resistance.
The spin-valve thin-film magnetic element is of an abutted junction type in which the variable magnetization of the free magnetic layer
104
is firmly pinned by the hard bias layers
105
located at both sides of the free magnetic layer
104
, improving the stability of the magnetization of the free magnetic layer
104
.
The magnetization of the free magnetic layer
104
is usually aligned in the track width direction under the influence of the hard bias layers
105
which are formed at both sides of the free magnetic layer
104
and which are magnetized in the track width direction. However, the influence of the hard bias layers
105
is largest at both ends of the free magnetic layer
104
, and the influence decreases toward the center of the free magnetic layer
104
.
FIGS. 36 and 37
are graphs showing the output profiles in the track width direction of the spin-valve thin-film magnetic element shown in FIG.
35
.
The read output of the spin-valve thin-film magnetic element has a profile in the read track width direction (in the X1 direction shown in FIG.
35
), and the midsection of the laminate
109
is a sensitive region
109
a
which substantially contributes to reading of the recorded magnetic field from the magnetic recording medium and which has a read output sufficiently high for exhibiting a magnetoresistance effect. The sensitive region
109
a
corresponds to the read track width Tw. On the other hand, regions at both sides of the sensitive region
109
a
in the laminate
109
are insensitive regions
109
b
having a low read output insufficient for substantially contributing to reading of the recorded magnetic field from the magnetic recording medium.
The sensitive region
109
a
and the insensitive regions
109
b
in the laminate
109
are determined by a microtrack profile method which will be described below.
In such a spin-valve thin-film magnetic element, instability in output is preferably low.
With increasing demands for improving recording density of magnetic recording onto medium, there are strong requirements for narrowing of a read track width to 1 &mgr;m or less, and further to 0.5 &mgr;m or less, and particularly to 0.4 &mgr;m or less as well as for prevention of reduction in output.
However, in the abutted junction type spin-valve thin-film magnetic element, when the track width is narrowed, the read output is decreased.
The read output profile described above is caused by the fact that insensitive regions
104
b
of the free magnetic layer
104
which are nearer to the hard bias layers
105
are more strongly influenced by the magnetic field from the hard bias layers
105
and the variable magnetization of the free magnetic layer
104
is more firmly pinned compared to a sensitive region
104
a
in the midsection of the free magnetic layer
104
corresponding to the sensitive region
109
a
. That is, the influence of the hard bias layers
105
is largest at both ends of the free magnetic layer
104
and the influence decreases toward the center of the free magnetic layer
104
, i.e., the influence decreases as the distance from the hard bias layers
105
is increased, and thus the insensitive regions
104
b
occur.
Herein, the insensitive regions
104
b
refer to the regions in which rotation of the variable magnetization of the free magnetic layer
104
is blunted, and do not correspond to a difference between the physical track width
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Watko Julie Anne
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