Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-05-10
2004-02-24
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S320000
Reexamination Certificate
active
06697234
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thin-film magnetic head provided with a magnetoresistive (MR) element, and more particularly to a thin-film magnetic head in which a crystallized layer is not formed on the surface of a shielding layer facing a MR element, magnetic properties are not degraded, and the effective gap length can be easily controlled.
2. Description of the Related Art
As thin-film magnetic heads provided with magnetoresistive elements (MR elements), anisotropic magnetoresistive (AMR) heads using an anisotropic magnetoresistance effect and giant magnetoresistive (GMR) heads using the spin-dependent scattering phenomenon of conduction electrons have been known. As an example of the GMR head, a spin-valve head in which a high magnetoresistance effect is exhibited in a small external magnetic field is disclosed in U.S. Pat. No. 5,159,513.
FIG. 19
is a schematic diagram which shows the structure of a conventional AMR head. In the conventional AMR head, an insulating layer
8
as a lower gap layer is formed on a lower shielding layer
7
composed of a magnetic alloy having the crystal structure of Sendust (Fe—Al—Si) or the like. An AMR element
10
is deposited on the insulating layer
8
. In the AMR element
10
, a nonmagnetic layer
12
is formed on a soft magnetic layer
11
, and a ferromagnetic layer (AMR material layer)
13
is further formed on the nonmagnetic layer
12
. Magnetic layers
15
are formed at both sides of the AMR element
10
, and conductive layers
16
are formed on the magnetic layers
15
. Furthermore, an insulating layer
18
as an upper gap layer is formed, and an upper shielding layer
19
is formed thereon.
In the AMR head having the structure described above, in order to prevent a rise in the temperature of the AMR element
10
due to heat generated by a steady-state sensing current, which may vary the electrical resistance of the ferromagnetic layer
13
, the upper and lower gap layers
8
and
18
are composed of alumina (Al
2
O
3
), and heat generated by the steady-state sensing current is gradually transmitted through the gap layers
8
and
18
to the shielding layers
7
and
19
, and thus the heat is dissipated.
In order to optimally operate such an AMR head, two bias magnetic fields must be applied to the ferromagnetic layer
13
which exhibits an anisotropic magnetoresistance effect.
A first bias magnetic field is used to make a change in the resistance of the ferromagnetic layer
13
linearly responsive to a magnetic flux from a magnetic medium. The first bias magnetic field is applied perpendicular to the surface of the magnetic medium (in the Z direction in
FIG. 19
) and parallel to the plane of the ferromagnetic layer
13
. The first bias magnetic field is usually referred to as a lateral bias. The soft magnetic layer
11
is magnetized in the Z direction by a magnetic field induced by a sensing current that is conducted by conductive layers
16
though the AMR element
10
, and a lateral bias is applied to the ferromagnetic layer
13
in the Z direction by the magnetization of the soft magnetic layer
11
.
A second magnetic field is usually referred to as a longitudinal bias, and is applied parallel to the magnetic medium and the plane of the ferromagnetic layer
13
(in the X direction in FIG.
19
). The longitudinal bias is applied so that Barkhausen noise, which is caused due to many domains formed in the ferromagnetic layer
13
, is suppressed, namely, a smooth change in resistance with decreased noise in response to the magnetic flux from the magnetic medium is enabled.
In order to suppress Barkhausen noise, the ferromagnetic layer
13
must be aligned in a single-domain state. There are two known methods for applying the longitudinal bias. In the first method, the magnet layers
15
are disposed at both sides of the ferromagnetic layer
13
and a leakage flux from the magnet layers
15
is used. In the second method, an exchange anisotropic magnetic field produced at the contact interface between an antiferromagnetic layer and a ferromagnetic layer is used.
As a GMR head in which exchange anisotropic magnetic coupling by an antiferromagnetic layer is used, a spin-valve type GMR head shown in
FIG. 20
is known.
The GMR head shown in
FIG. 20
differs from the AMR head shown in
FIG. 19
in a GMR element
20
which is provided instead of the AMR element
10
.
The GMR element
20
includes a free ferromagnetic layer
22
, a nonmagnetic intermediate layer
23
, a pinned ferromagnetic layer
24
, and an antiferromagnetic layer
25
.
In the structure shown in
FIG. 20
, the free ferromagnetic layer
22
must be magnetized in the track width direction (in the X direction in
FIG. 20
) while the free ferromagnetic layer
22
is aligned in a single-domain state by applying a bias in the track width direction by the magnet layers
15
, and the pinned ferromagnetic layer
24
must be magnetized in the Z direction in
FIG. 20
while the pinned ferromagnetic layer
24
is aligned in a single-domain state by applying a bias in a direction perpendicular to the magnetization direction of the free ferromagnetic layer
22
. That is, the magnetization direction of the pinned ferromagnetic layer
24
should not be changed by the magnetic flux from a magnetic medium (in the Z direction in FIG.
20
), and the linear responsiveness of the magnetoresistance can be obtained by a change in the magnetization direction of the free ferromagnetic layer
22
within a range of 90±&thgr;° in relation to the magnetization direction of the pinned ferromagnetic layer
24
.
A relatively large bias magnetic field is required in order to pin the magnetization of the pinned ferromagnetic layer
24
in the Z direction in
FIG. 20
, and the larger the better. A bias magnetic field of at least 100 Oe is required in order to overpower a demagnetizing field in the Z direction and to prevent the magnetization direction from being influenced by the magnetic flux from the magnetic medium. As a method for generating the bias magnetic field, in the structure shown in
FIG. 20
, an exchange anisotropic magnetic field, which is produced by providing the antiferromagnetic layer
25
in contact with the pinned ferromagnetic layer
24
, is used.
Accordingly, in the structure shown in
FIG. 20
, since the magnetization of the pinned ferromagnetic layer
24
is pinned in the Z direction by exchange anisotropic coupling produced by providing the antiferromagnetic layer
25
in contact with the pinned ferromagnetic layer
24
, when a fringing magnetic field is applied from a magnetic medium moving in the Y direction, the electrical resistance of the GMR element
20
is changed in response to a change in the magnetization direction of the free ferromagnetic layer
22
, and thus the fringing magnetic field from the magnetic medium can be detected by the change in the electrical resistance.
A bias applied to the free ferromagnetic layer
22
secures the linear responsiveness and suppresses Barkhausen noise resulting from the formation of many domains. A similar method to that of the longitudinal bias in the AMR head is employed in the structure shown in FIG.
20
. That is, magnetic layers
15
are provided at both sides of the free ferromagnetic layer
22
, and a leakage flux from the magnetic layers
15
is used as a bias.
With respect to the conventional thin-film magnetic heads, since the lower shielding layer
7
is composed of a magnetic alloy having the crystal structure of Fe—Al—Si (Sendust), Ni—Fe—Nb, or the like, the surface of the lower shielding layer
7
is uneven. Thereby, if a MR element is formed on the lower shielding layer
7
with the thin lower gap layer
8
having a thickness of approximately 550 angstroms therebetween, unevenness and pin holes may occur in the surface of the MR element. The unevenness and the like occurs in the surface of the MR element because the MR element, which comprises a laminate including thin films, is as thin as 0.03 &mgr;m and is easily influenced by the surface roughne
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Renner Craig A.
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