Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-11-26
2002-12-31
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06501627
ABSTRACT:
TECHNICAL FIELD
The present invention relates to spin-valve magnetoresistive heads, and more particularly to a pin-valve magnetoresistive head having on terminal sides laminations for applying a bias magnetic field to a free magnetic layer and a composite-type head and a drive using the same.
BACKGROUND ART
At present, an AMR (Anisotropic Magnetoresistive) device is most frequently used in a magnetic head mounted in a magnetic recording medium recording/reproduction apparatus such as an HDD (Hard Disk Drive). However, as recording density increases, a full-scale movement toward practical use of a spin-valve magnetoresistive magnetic head (hereinafter, an SVMR head) using a more sensitive SVMR (Spin-valve Magnetoresistive) film has started, and the commercial production of the SVMR head has begun.
A common SVMR head includes a basic lamination as shown in
FIG. 1. A
device part is formed of an SVMR film formed by layering an antiferromagnetic layer
102
, a pinned magnetic layer
103
, a nonmagnetic layer
104
, and a free magnetic layer in the order described on a substrate
101
. A width C of the device part serves as a magnetic sensitive part S for detecting a signal magnetic field Hsig from a magnetic recording medium such as a hard disk. The SVMR head has terminal parts T
1
A and T
1
B on both ends of the device part in the direction of the width C. In the terminal parts T
1
A and T
1
B, conductive electrode terminals
106
A and
106
B are provided on hard ferromagnetic layers
107
A and
107
B, for instance. The hard ferromagnetic layers
107
A and
107
B are magnetizing bias means for magnetizing the free magnetic layer
105
in the direction of an arrow (the direction of an axis of easy magnetization) from the terminal parts T
1
A and T
1
B.
FIG. 2
shows an SVMR head
200
of another type. The SVMR head
200
is of a type called a terminal overlay. A basic structure is equal to that of the SVMR head
100
shown in FIG.
1
. An SVMR device part is formed by layering an antiferromagnetic layer
202
, a pinned magnetic layer
203
, a nonmagnetic layer
204
, and a free magnetic layer
205
in the order described on a substrate
201
. Hard ferromagnetic layers
207
A and
207
B are provided on the terminal part T
2
A and T
2
B sides. However, electrode terminals
206
A and
206
B of terminal parts T
2
A and T
2
B are formed on both ends of the device part so as to cover parts thereof. The overlay-type SVMR head
200
has the magnetic sensitive part S narrower than the device width C by the width of an overlay by the terminal parts T
2
A and T
2
B. Thus, the overlay-type SVMR head
200
is devised so that reading and reproduction can be performed even if the track width of the magnetic recording medium is narrowed as the magnetic recording density increases.
FIG. 3
shows yet another overlay-type SVMR head
300
. An SVMR film is formed by layering an antiferromagnetic layer
302
, a pinned magnetic layer
303
, a nonmagnetic layer
304
, and a free magnetic layer
305
in the order described on a substrate
301
. Terminal parts T
3
A and T
3
B are formed by ferromagnetic layers
307
A and
307
B and terminal electrodes
306
A and
306
B covering both ends of the SVMR film. As the ferromagnetic layers
307
A and
307
B, single-layer hard ferromagnetic layers or single-layer antiferromagnetic layers are employed. A bias magnetic field to set the magnetization orientation of the free magnetic layer in the direction of an arrow is applied by a static magnetic field if the ferromagnetic layers
307
A and
307
B are the single-layer hard ferromagnetic layers, and by an exchange coupling magnetic field if the ferromagnetic layers
307
A and
307
B are the single-layer antiferromagnetic layers.
Unlike the above-described SVMR heads
100
and
200
shown in
FIGS. 1 and 2
, in the SVMR head
300
shown in
FIG. 3
, the SVMR film formed of the antiferromagnetic layer
302
, the pinned magnetic layer
303
, the nonmagnetic layer
304
, and the free magnetic layer
305
extends from the terminal part T
3
A side to the other terminal T
3
B side. However, a part reacting to an external magnetic field as the SVMR head
300
is a part between the terminal parts T
3
A and T
3
B. Therefore, in this specification, a part of an SVMR head which parts includes an SVMR film and magnetically senses the signal magnetic field Hsig is referred to as a device part. Further, parts on both sides of the device part which parts include conductive electrode terminals and, in some cases, lamination parts formed below the electrode terminals may be referred to as terminal parts.
The SVMR head
100
applies a bias magnetic field from the hard ferromagnetic layers
107
A and
107
B on the terminal part sides to the free magnetic layer
105
. Therefore, such an uneven state is entered that the bias magnetic field from the hard ferromagnetic layers
107
A and
107
B is strong on both ends of the free magnetic layer
105
and weak in a center part thereof. Accordingly, it is difficult to make the free magnetic layer
105
to act as a single magnetic domain, thus, in some cases, preventing the signal magnetic field Hsig from the magnetic recording medium from being detected with sufficient sensitivity.
Further, leakage magnetic fields from the hard ferromagnetic layers
107
A and
107
B extend as far as the pinned magnetic layer
103
. Therefore, there is a problem of an inclination of the magnetization direction of the pinned magnetic layer
103
that should be fixed parallel to the signal magnetic field Hsig.
Moreover, the SVMR head
100
, in its production process, has the SVMR film formed by layering the antiferromagnetic layer
102
, the pinned magnetic layer
103
, the nonmagnetic layer
104
, and the free magnetic layer
105
in the order described on the substrate
101
, and, normally, is etched thereafter to have the device part of a given size. By this etching, nonmagnetic parts N, which have such disordered crystal states as to lose magnetism, are formed on both ends of the device part. The nonmagnetic parts N are also formed on both ends of the free magnetic layer
105
reacting to the signal magnetic layer Hsig. This causes a problem that the width of the device part for magnetic sensing becomes narrower than is designed and a problem that noises are generated.
The overlay-type SVMR head
200
shown in
FIG. 2
has the device part formed by etching as the SVMR head
200
of FIG.
1
. If the electrode terminals
206
A and
206
B are to be formed to exactly cover the above-described nonmagnetic parts N, the SVMR head
200
can be formed to maintain its sensitivity and have a narrower device width. However, it is very difficult to position the electrode terminals
206
A and
206
B exactly on the nonmagnetic parts N in the production process. Further, both ends of the free magnetic layer
205
which ends are overlaid with the electrode terminals
206
A and
206
B still functions as a free magnetic layer. Therefore, both ends of the free magnetic layer
205
react to the signal magnetic field Hsig, which may cause noise generation. Further, in the case of reading a hard disk having a narrow track width, these parts read adjacent tracks, thus causing so-called crosstalk to be generated.
Further, the overlay-type SVMR head
300
has the ferromagnetic layers
307
A and
307
B flatly contacting the free magnetic layers
305
to apply the strong bias magnetic field thereto from the terminal parts. However, if the ferromagnetic layers
307
A and
307
B are single-layer hard ferromagnetic layers, it is difficult to secure a sufficient thickness in the terminal parts. This prevents application of a bias magnetic field required for controlling the magnetization direction of the free magnetic layer
305
, thus precluding the device part from being sensitive to the signal magnetic field Hsig.
On the other hand, if the ferromagnetic layers
307
A and
307
B are single-layer antiferromagnetic layers, the bias magnetic field is applied from the antiferromagnetic layers to the free magnetic layer
305
by the exchange
Aoshima Ken-ichi
Kanai Hitoshi
Kane Junichi
Noma Kenji
Fujitsu Limited
Greer Burns & Crain Ltd.
Miller Brian E.
LandOfFree
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