Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-07-19
2004-04-13
Heinz, A. J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06721148
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to magnetoresistive devices, and more particularly to magnetoresistive sensors and heads that include a magnetoresistive element having an antiferromagnetic layer and two magnetic layers sandwiching a non-magnetic interlayer, as well as to a process for producing the magnetoresistive element.
2. Description of the Related Art
Recent magnetic disks capable of high-density recording require a highly sensitive read head. One example of such a highly sensitive read head in disclosed in
Physical Review B
, Vol. 43, pp. 1297-1300, “Giant Magnetoresistance Effect in Soft Magnetic Multi-layered Film”, which shows a structure having two magnetic layers separated by a non-magnetic metal layer, and in which one of the magnetic layers receives an exchange bias magnetic field from an antiferromagnetic layer.
The above-mentioned thesis points out that resistance (R) in the multi-layered film has a component which changes in proportion to cos &thgr;, where &thgr; represents the angle between the directions of magnetization of the two magnetic layers. This phenomenon is referred to as the giant magnetoresistance effect (GMR) or spin valve effect.
The giant magnetoresistive head works in different modes depending on whether a sense current flows along or across the layer plane (referred to as “current in the plane” or CIP mode and “current perpendicular to the plane” or CPP mode, respectively). The MR ratio in CPP mode is more than twice as high as that in CIP mode at room temperature.
Among highly sensitive read heads is a tunnel magnetoresistive (TMR) head, which has attracted attention in recent years. The TMR head utilizes a ferromagnetic tunnel junction due to a tunnel barrier layer held between two ferromagnetic layers. Its structure is disclosed in Japanese Laid-open Patent No. 103014/1992. The structure is quite similar to that of a giant magnetoresistive head in CPP mode, the only difference being the tunnel barrier layer acting as an insulating layer which replaces the non-magnetic metal layer in the giant magnetoresistive head.
The conventional giant magnetoresistive head in CIP mode has a magnetoresistive film (GMR film)
30
which is composed of a free layer
35
, a non-magnetic metal layer (Cu layer)
40
, a pinned layer
45
, and an antiferromagnetic layer
50
, which are formed one on top of another as shown in FIG.
16
. The magnetization of the pinned layer
45
is pinned in the direction of element height by the exchange bias magnetic field from the antiferromagnetic layer
50
. In general, the axis of easy magnetization of the free layer
35
is made parallel to the direction of the track width of the head.
The giant magnetoresistive head in CIP mode is produced by a process which consists of a first step of sequentially forming a magnetic shield layer
10
, a magnetic gap layer
20
, and a magnetoresistive (GMR) film
30
on a substrate
5
, a second step of arranging permanent magnets
60
and electrode films
70
at both ends of the GMR film
30
, and a third step of forming a magnetic gap layer
80
, with a magnetic shield film
90
interposed thereunder.
The giant magnetoresistive head in CPP mode also has a magnetoresistive (GMR) film
30
which is composed of a free layer
35
, a Cu layer
40
, a pinned layer
45
, and an antiferromagnetic layer
50
, which are formed one on top of another as shown in FIG.
17
. The magnetization of the pinned layer
45
is pinned in the direction of element height by the exchange bias magnetic field from the antiferromagnetic layer
50
. The axis of easy magnetization of the free layer
35
is made parallel to the direction of the track width of the head.
The giant magnetoresistive head in CPP mode is produced by a process which consists of a first step of sequentially forming a magnetic shield layer
10
(which functions also as a lower electrode film) and a magnetoresistive (GMR) film
30
on a substrate
5
, a second step of patterning the GMR film
30
, a third step of arranging permanent magnets
60
at both ends of the GMR film
30
, a fourth step of arranging insulating films
65
of Al
2
O
3
such that they cover the permanent magnets
60
, and a fifth step of forming an upper shield layer
90
which functions also as an upper electrode film. The insulating films prevent current from flowing into the permanent magnet.
The tunnel magnetoresistive head is quite similar in structure to the above-described giant magnetoresistive head in CPP mode. The only difference between them is replacement of the magnetoresistive film
30
by the tunnel magnetoresistive film
31
which is composed of a free layer
35
, a tunnel barrier layer
41
, a pinned layer
45
, and an antiferromagnetic layer
50
as shown in FIG.
18
.
Both the giant magnetoresistive film and the tunnel magnetoresistive film (collectively referred to as “magnetoresistive film”) have permanent magnet films arranged at both sides thereof. The permanent magnet film applies a longitudinal bias field in the direction of track width to the magnetoresistive film so as to reduce Barkhausen noise attributable to the magnetic domain structure in the free layer. The longitudinal bias field applied by the permanent magnet film is distributed as shown in
FIG. 19
, which shows weakness at the center of the magnetoresistive element (due to the effect of the shield film) and an increase far from the center through which the track width extends.
The magnetic domain structure, which causes noise in the free layer, tends to occur at both ends in the track width direction where there is a strong self-demagnetizing field. Therefore, it is desirable to apply a stronger longitudinal bias field to both ends of the free layer in the track width direction.
The ever-increasing recording density in magnetic recording requires the magnetic head to have a narrower track width and a higher reproducing sensitivity.
The result of reducing the track width of the magnetic head is a decrease in the distance between the permanent magnets arranged at both ends of the magnetoresistive element. Decreasing this distance means that the area receiving the strong longitudinal bias field in the free layer increases relative to the track width. In other words, the longitudinal bias field, which is applied to the center of the free layer through which the track width extends, increases with the decreasing track width of the magnetic head.
On the other hand, the increasing longitudinal bias field causes the rotation magnetization of the free layer to decrease due to the signal magnetic field at the center of the free layer through which the track width extends. This leads to a decrease in reproducing sensitivity. Therefore, it is desirable to apply as small a longitudinal bias field as possible to the center of the track of the free layer, so as to secure good sensitivity.
One possible way to improve the reproducing sensitivity is to reduce the thickness of the permanent magnet film, thereby decreasing the longitudinal bias field applied to the center of the free layer through which the track width extends. However, the reduction in thickness of the permanent magnet film results in insufficient longitudinal bias field at the ends of the free layer, which leads to the occurrence of magnetic domains, which in turn produces Barkhausen noise.
The foregoing presents difficulties in achieving both improvement in reproducing sensitivity and reduction in Barkhausen noise if the magnetic head has a narrow track.
SUMMARY OF THE INVENTION
The present invention was completed in view of the foregoing. Thus, one of the objects of the present invention is to provide a magnetoresistive element, a magnetoresistive head provided therewith, or a process for production thereof, with a high reproducing sensitivity of low Barkhausen noise even though the track width is very narrow. Furthermore, another one of the objects of the invention is to provide a magnetic recording apparatus equipped with the magnetoresistive head that may be combined
Ishikawa Chiaki
Suzuki Yoshio
Castro Angel
Heinz A. J.
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
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