Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-06-02
2003-02-11
Ometz, David L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S314000
Reexamination Certificate
active
06519122
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spin-valve thin-film element which causes a change in electrical resistance by the relationship between the direction of pinned magnetization of a pinned magnetic layer and the direction of variable magnetization of a free magnetic layer affected by an external magnetic field, and to a thin-film magnetic head provided with the spin-valve thin-film element. In particular, the present invention relates to a spin-valve thin-film element having a biasing conductive layer in which a current applied to the biasing conductive layer can control the variable magnetization direction of the free magnetic layer, and exhibiting high heat resistance and reliability and small asymmetry, and to a thin-film magnetic head provided with the spin-valve thin-film element.
2. Description of the Related Art
Spin-valve thin-film elements belong to giant magnetoresistive (GMR) elements and detect magnetic fields recorded on recording media such as hard disks. Among the GMR elements, the spin-valve thin-film elements have relatively simplified structures exhibit large rates of change in resistance in response to external magnetic fields, and are sensitive to weak magnetic fields. The spin-valve thin-film elements are classified into single spin-valve thin-film elements and dual spin-valve thin-film elements.
FIG. 21
is a cross-sectional view of a conventional spin-valve thin-film element viewed from an opposing face opposing a recording medium. This spin-valve thin-film element is of a bottom type including a pair of composites, each including an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic layer, and a free magnetic layer. In
FIG. 21
, the magnetic recording medium, such as a hard disk moves in the Z direction, and generates a fringing magnetic field in the Y direction.
An antiferromagnetic layer
20
composed of a NiO alloy, a FeMn alloy, or a NiMn alloy is formed on an underlying layer
10
composed of tantalum (Ta). A pinned magnetic layer
30
composed of cobalt (Co) or a NiFe alloy is formed on the antiferromagnetic layer
20
. Since the pinned magnetic layer
30
is in contact with the antiferromagnetic layer
20
, an exchange coupling magnetic field (an exchange anisotropic magnetic field) is generated between the pinned magnetic layer
30
and the antiferromagnetic layer
20
and the pinned magnetization of the pinned magnetic layer
30
is pinned, for example, in the Y direction in the drawing.
A nonmagnetic conductive layer
40
composed of copper (Cu) is formed on the pinned magnetic layer
30
, and a free magnetic layer
50
composed of the same material as that of the pinned magnetic layer
30
is formed on the nonmagnetic conductive layer
40
. The free magnetic layer
50
is covered with a protective layer
70
composed of Ta.
Hard biasing layers
60
composed of, for example, a cobalt-platinum (Co—Pt) alloy are formed on both sides of the composite from the underlying layer
10
to the protective layer
70
. The hard biasing layers
60
are magnetized in the direction opposite to the X
1
direction in the drawing so that the variable magnetization of the free magnetic layer
50
is oriented in the direction opposite to the X
1
direction. Thus, the variable magnetization of the free magnetic layer
50
and the pinned magnetization of the pinned magnetic layer
30
are perpendicular to each other.
Conductive layers
80
composed of Cu or the like are formed on the hard biasing layers
60
and lead a detecting current to the pinned magnetic layer
30
, the nonmagnetic conductive layer
40
, and the free magnetic layer
50
.
In this spin-valve thin-film element, the fringing magnetic field from the magnetic recording medium such as the hard disk changes a variable magnetization of the free magnetic layer
50
oriented in the direction opposite to the X
1
direction. Such a change in the variable magnetization causes a change in electrical resistance of the spin-valve thin-film element in relation to the pinned magnetization of the pinned magnetic layer
30
. As a result, the fringing magnetic field from the magnetic recording medium is detected as a change in voltage due to the change in the electrical resistance.
It is preferable in the spin-valve thin-film element that the variable magnetization of the free magnetic layer
50
and the pinned magnetization of the pinned magnetic layer
30
be close to 90 degrees in order to ensure high heat resistance, high reliability, and small symmetry. The direction of the variable magnetization of the free magnetic layer
50
, however, is undesirably tilted from 90 degrees by a magnetostatic coupling magnetic field of the pinned magnetic layer
30
and a current magnetic field of the detecting current.
With reference to
FIG. 22
, when a magnetostatic coupling magnetic field Hp
4
of the pinned magnetic layer
30
and a current magnetic field Hi
4
of a detecting current i
4
are formed in the same direction (assisting direction), the variable magnetization Hf
10
of the free magnetic layer
50
is tilted as variable magnetization Hf
11
towards a combined magnetization moment of the magnetostatic coupling magnetic field Hp
4
and the current magnetic field Hi
4
.
With reference to
FIG. 23
, when a magnetostatic coupling magnetic field Hp
5
of the pinned magnetic layer
30
and a current magnetic field Hi
5
of a detecting current i
5
are formed in different directions (counter directions) from each other and when the magnetostatic coupling magnetic field Hp
5
is larger than the current magnetic field Hi
5
, a variable magnetization Hf
20
of the free magnetic layer
50
is tilted as variable magnetization Hf
21
towards the combined moment of the magnetostatic coupling magnetic field Hp
5
and the current magnetic field Hi
5
, that is, in the direction of the magnetostatic coupling magnetic field Hp
5
.
With reference to
FIG. 24
, when a magnetostatic coupling magnetic field Hp
6
of the pinned magnetic layer
30
and a current magnetic field Hi
6
of a detecting current i
6
are formed in different directions (counter directions) from each other and when the magnetostatic coupling magnetic field Hp
6
is smaller than the current magnetic field Hi
6
, a variable magnetization Hf
30
of the free magnetic layer
50
is tilted as variable magnetization Hf
31
towards the combined moment of the magnetostatic coupling magnetic field Hp
6
and the current magnetic field Hi
6
, that is, in the direction of the current magnetic field Hi
6
.
As shown in
FIGS. 22
to
24
, the tilt of the variable magnetization of the free magnetic layer
50
does not maintain a perpendicular relationship between the variable magnetization of the free magnetic layer
50
and the pinned magnetization of the pinned magnetic layer
30
. Thus, heat resistance and reliability are deteriorated, and asymmetry is increased. Accordingly, this spin-valve thin-film element may erroneously process signals from the magnetic recording medium.
FIG. 25
is a cross-sectional view of another conventional spin-valve thin-film element viewed from an opposing face opposing a recording medium. This spin-valve thin-film element is of a dual type including a free magnetic layer and a pair of composites formed on both faces thereof, each including a nonmagnetic conductive layer, a pinned magnetic layer, and an antiferromagnetic layer.
This dual spin-valve thin-film element including two triple-layered composites, each including the free magnetic layer, the nonmagnetic conductive layer, and the pinned magnetic layer, exhibits a larger rate of change in resistance compared to the single spin-valve thin-film element shown in
FIG. 21
, and is advantageous considering trends toward high-density recording. In
FIG. 25
, the magnetic recording medium, such as a hard disk, moves in the Z direction and generates a fringing magnetic field in the Y direction.
In the dual spin-valve thin-film element, an underlying layer
41
, an antiferromagnetic layer
42
, a lower pinned magnetic layer
43
,
Alps Electric Co. ,Ltd.
Brinks Hofer Giloson & Lione
Ometz David L.
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