Shield design for stable magnetoresistive head

Details Shield design for stable magnetoresistive head Shield design for stable magnetoresistive head

2000-02-18

2002-09-03

Evans, Jefferson (Department: 2652)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

C360S324120

Reexamination Certificate

active

06445552

ABSTRACT:

FIELD OF THE INVENTION
The field of invention relates to direct access data storage, generally. More specifically, the invention relates to compensating for the effect of image poles within a magnetic head.
BACKGROUND
Hardware systems often include memory storage devices having media on which data can be written to and read from. A direct access storage device (DASD or disk drive) incorporating rotating magnetic disks are commonly used for storing data in magnetic form. Magnetic heads, when writing data, record concentric, radially spaced information tracks on the rotating disks.
Magnetic heads also typically include read sensors that read data from the tracks on the disk surfaces. In high capacity disk drives, magnetoresistive (MR) read sensors, the defining structure of MR heads, can read stored data at higher linear densities than thin film heads. An MR head detects the magnetic field(s) through the change in resistance of its MR sensor. The resistance of the MR sensor changes as a function of the direction of the magnetic flux that emanates from the rotating disk.
One type of MR sensor, referred to as a giant magnetoresistive (GMR) effect sensor, takes advantage of the GMR effect. In GMR sensors, the resistance of the MR sensor varies with direction of flux from the rotating disk and as a function of the spin dependent transmission of conducting electrons between magnetic layers separated by a non-magnetic layer (commonly referred to as a spacer) and the accompanying spin dependent scattering within the magnetic layers that takes place at the interface of the magnetic and non-magnetic layers.
GMR sensors using two layers of magnetic material separated by a layer of CMR promoting non-magnetic material are generally referred to as spin valve (SV) sensors. In an SV sensor, one of the magnetic layers, referred to as the pinned layer, has its magnetization direction “pinned” via the influence of exchange coupling with an antiferromagnetic layer. Due to the relatively high internal anisotropy field associated with the pinned layer, the magnetization direction of the pinned layer typically does not rotate from the flux lines that emanate from the rotating disk. The magnetization direction of the other magnetic layer (commonly referred to as a free layer), however, is free to rotate with respect to the flux lines that emanate/terminate from/to the rotating disk.
FIG. 1
shows a prior art SV sensor structure
100
where the pinned layer is implemented as a structure
120
having two ferromagnetic films
121
,
122
(also referred to as MP
2
and MP
1
layers, respectively) separated by a non ferromagnetic film
123
(such as ruthenium Ru) that provides antiparallel coupling of the two ferromagnetic films
121
,
122
. Sensor structures such as that
100
shown in
FIG. 1
are referred to as AP sensors in light of the antiparallel magnetic relationship between films
121
,
122
. Similarly, structure
120
may also be referred to as an AP layer
120
.
FIG. 1
shows an AP sensor
100
comprising a seed layer
102
formed upon a gap layer
101
. The seed layer
102
helps properly form the microstructure of the antiferromagnetic (AFM) layer
105
. Over seed layer
102
is a free layer
103
. The antiferromagnetic (AFM)
105
layer is used to pin the magnetization direction of the MP
2
layer
121
. MP
1
layer
122
is separated from free layer
103
by spacer layer
104
. Note that free magnetic layer
103
may be a multilayer structure having two or more ferromagnetic layers.
A problem with structures such as the sensor
100
shown in
FIG. 1
, is the stability of the free layer
103
as sensor dimensions are continually reduced.
SUMMARY OF INVENTION
A multilayer structure is disclosed having a magneto resistive free layer. The multilayer structure is between a pair of shields and the shields are separated by at least two spacings. A first of the spacings is at least the length of the multilayer structure. A second of the spacings is greater than the first spacing.


REFERENCES:
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patent: 5768067 (1998-06-01), Saito et al.
patent: 5784225 (1998-07-01), Saito et al.
patent: 5850325 (1998-12-01), Miyauchi et al.
patent: 5869963 (1999-02-01), Saito et al.
patent: 5874886 (1999-02-01), Araki et al.
patent: 5898548 (1999-04-01), Dill et al.
patent: 6061210 (2000-05-01), Gill
patent: 6198609 (2001-05-01), Barr et al.
patent: 6243241 (2001-06-01), Kanai
“TTB: Barkhausen Noise Quantification Using a Derivative Approximation”, IBM Technical Disclosure Bulletin, Nov. 1991, pp 460-465.

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