Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-07-11
2004-03-30
Mai, Anh (Department: 2832)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324120, C360S324000
Reexamination Certificate
active
06714388
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to magnetic sensing elements mainly used for magnetic sensors, hard disk drives, etc., and more particularly, to a magnetic sensing element having an improved magnetic sensitivity and a method for making the same.
2. Description of the Related Art
FIG. 32
is a sectional view of a conventional magnetic sensing element, viewed from a surface facing a recording medium.
The magnetic sensing element shown in
FIG. 32
is a spin-valve magnetic sensing element which is one type of giant magnetoresistive (GMR) element using a giant magnetoresistance effect and which detects a recorded magnetic field from a magnetic recording medium, such as a hard disk.
The spin-valve magnetic sensing element includes a multilayer film
8
including a substrate
1
, an underlayer
2
, a first antiferromagnetic layer
3
, a pinned magnetic layer
4
, a nonmagnetic material layer
5
, a free magnetic layer
6
, and a protective layer
7
deposited in that order from the bottom; a pair of ferromagnetic layers
9
formed on both sides of the multilayer film
8
; a pair of second antiferromagnetic layers
10
formed on the pair of ferromagnetic layers
9
; and a pair of electrode layers L formed on the pair of second antiferromagnetic layers
10
.
In general, Pt—Mn alloy films are used for the first antiferromagnetic layer
3
and the second antiferromagnetic layers
10
; Ni—Fe alloy films are used for the pinned magnetic layer
4
, the free magnetic layer
6
, and the ferromagnetic layers
9
; a Cu film is used for the nonmagnetic material layer
5
; Ta films are used for the underlayer
2
and the protective layer
7
; and Cr films are used for the electrode layers L.
The magnetization of the pinned magnetic layer
4
is aligned in a single domain state in the Y direction (the direction of a fringing magnetic field from the recording medium, i.e., in the height direction) by an exchange anisotropic magnetic field with the first antiferromagnetic layer
3
.
Each of the ferromagnetic layers
9
is aligned in a single domain state in the X direction by an exchange anisotropic magnetic field with the second antiferromagnetic layer
10
. The free magnetic layer
6
and the ferromagnetic layers
9
are in contact with each other at joints J, thus forming a continuous ferromagnetic body. The free magnetic layer
6
is aligned in a single domain state in the X direction by a so-called “exchange bias system”. In the exchange bias system, surface magnetic charges do not occur at both end faces (joints J) of the free magnetic layer
6
, and the magnitude of a demagnetizing field generated in the free magnetic layer
6
can be decreased.
In the magnetic sensing element, a sensing current is supplied from one of the electrode layers L through the second antiferromagnetic layer
10
and the ferromagnetic layer
9
to the free magnetic layer
6
, the nonmagnetic layer
5
, and the pinned magnetic layer
4
. A recording medium, such as a hard disk, travels in the Z direction, and when a fringing magnetic field from the recording medium is applied in the Y direction, the magnetization direction of the free magnetic layer
6
is changed from the X direction to the Y direction. Electrical resistance changes due to the relationship between the varying magnetization direction of the free magnetic layer
6
and the pinned magnetization direction of the pinned magnetic layer
4
exemplify the magnetoresistance effect. This effect can be detected by a voltage change resulting from electrical resistance changes in the fringing magnetic field from the magnetic recording medium.
In order to fabricate the magnetic sensing element shown in
FIG. 32
, the underlayer
2
, the first antiferromagnetic layer
3
, the pinned magnetic layer
4
, the nonmagnetic layer
5
, the free magnetic layer
6
, and the protective layer
7
are deposited on the substrate
1
, each being a thin film with a uniform thickness, and then portions other than a portion for forming the multilayer film
8
shown in
FIG. 32
are removed by ion milling. Next, the ferromagnetic layers
9
are formed so as to come into contact with side faces
8
a
of the multilayer film
8
, and the second antiferromagnetic layers
10
and the electrode layers L are further deposited on the ferromagnetic layers
9
.
That is, in the magnetic sensing element shown in
FIG. 32
, the side faces
8
a
of the multilayer film
8
are interfaces trimmed by milling. Even if the ferromagnetic layers
9
are deposited on such interfaces trimmed by milling so as to be in contact with the interfaces, it is difficult to form a continuous ferromagnetic body in which the free magnetic layer
6
and the ferromagnetic layers
9
are joined to each other at the joints J, and therefore it is difficult to align the free magnetic layer
6
stably in a single domain state in the X direction.
Since the joints J between the free magnetic layer
6
and the ferromagnetic layers
9
are on the side faces
8
a
of the multilayer film
8
, it is difficult to magnetically couple the free magnetic layer
6
and the ferromagnetic layers
9
to each other. For this reason, it is also difficult to align the free magnetic layer
6
stably in a single domain state in the X direction.
Additionally, if an angle &thgr;1 of inclination of the side face
8
a
of the multilayer film
8
is decreased in order to stabilize the magnetic coupling between the free magnetic layer
6
and the ferromagnetic layers
9
, it becomes difficult to form the width of the free magnetic layer
6
in the track width direction (X direction) in a predetermined range.
Moreover, in order to join the free magnetic layer
6
and the ferromagnetic layers
9
reliably in the structure shown in
FIG. 32
, the thickness of the ferromagnetic layer
9
must be increased. However, if the thickness of the ferromagnetic layer
9
is increased, the unidirectional anisotropic magnetic field of the ferromagnetic layer
9
is decreased, resulting in a difficulty in applying a stable longitudinal bias to the free magnetic layer
6
. If the thickness of the ferromagnetic layer
9
is increased, insensitive regions occur at both ends of the free magnetic layer
6
, and therefore, satisfactory read sensitivity cannot be obtained in an element with a narrow track width at 0.2 &mgr;m or less.
As described above, in the conventional magnetic sensing element shown in
FIG. 32
using the exchange bias system, it is difficult to align the free magnetic layer
6
stably in a single domain state by applying a stable longitudinal bias to the free magnetic layer
6
.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a magnetic sensing element using the exchange bias system and a method for fabricating the same, in which the free magnetic layer can be aligned stably in a single domain state in the X direction, and magnetic sensitivity can be improved.
In accordance with the present invention, a magnetic sensing element includes a multilayer film including a first antiferromagnetic layer; a pinned magnetic layer, the magnetization direction of the pinned magnetic layer being pinned by the first antiferromagnetic layer; a nonmagnetic material layer; a free magnetic layer, the magnetization direction of the free magnetic layer varying in response to an external magnetic field; a nonmagnetic layer; a pair of ferromagnetic layers; a pair of second antiferromagnetic layers; a first electrode layer; a second electrode layer; and a track width region comprising a central region and pair of sides, wherein the multilayer film has a characteristic track width direction. In the magnetic sensing element, the nonmagnetic layer has a uniform thickness, or the thickness in the central region of the nonmagnetic layer is larger than in its side regions; the pair of ferromagnetic layers are provided on the upper surface of the nonmagnetic layer, the pair of ferromagnetic layers at a predetermined distance apart from one another in the track width direction; the pair of the second
Hasegawa Naoya
Umetsu Eiji
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Mai Anh
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