Bilayer seed layer for spin valves

Details Bilayer seed layer for spin valves Bilayer seed layer for spin valves

2000-07-13

2003-05-06

Letscher, George J. (Department: 2653)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

Reexamination Certificate

active

06560078

ABSTRACT:

FIELD OF THE INVENTION
The field of invention relates to MR head technology generally; and more specifically, to seed layer structures that may be used to form a high sensitivity MR 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 GMR 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/terminate from/to 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/upon the rotating disk.
“Bottom” spin valves are spin valves having an antiferromagnetic layer formed prior to the formation of free layer.
FIG. 1
shows a prior art SV sensor
100
comprising a seed layer
102
formed upon a gap layer
101
. The sensor
100
of
FIG. 1
is formed, layer by layer in the +x direction. Over seed layer
102
is an antiferromagnetic (AFM) layer
103
. The seed layer
102
helps properly form the microstructure of the antiferromagnetic (AFM) layer
103
. The AFM layer
103
is used to pin the magnetization direction of the pinned layer
104
. Pinned layer
104
is separated from free layer
105
by the non magnetic, GMR promoting, spacer layer
119
. Note that free magnetic layer
105
may be a multilayer structure having two or more ferromagnetic layers.
FIG. 2
shows another prior art “bottom” SV sensor structure
200
where the pinned layer is implemented as a structure
220
having two ferromagnetic films
221
,
222
(also referred to as MP2 and MP1 layers, respectively) separated by a non ferromagnetic film
223
(such as ruthenium Ru) that provides antiparallel coupling of the two ferromagnetic films
221
,
222
. Sensor structures such as that
200
shown in
FIG. 2
are referred to as AP sensors in light of the antiparallel magnetic relationship between films
221
,
222
. Similarly, structure
220
may also be referred to as an AP layer
220
.
FIG. 2
shows an AP sensor
200
comprising a seed layer
202
formed upon a gap layer
201
. Over seed layer
202
is an antiferromagnetic (AFM) layer
203
. The seed layer
202
helps properly form the microstructure of AFM layer
203
. The antiferromagnetic (AFM)
203
layer used to pin the magnetization direction of the MP2 layer
221
. MP1 layer
222
is separated from free layer
205
by spacer layer
204
. Note that free layer
205
may be a multilayer structure having two or more ferromagnetic layers.
Problems with forming the bottom sensors
100
,
200
shown in
FIGS. 1 and 2
include forming a seed layer
102
,
202
with a microstructure that suitably influences the microstructure of the AFM layer
103
,
203
.
SUMMARY OF INVENTION
An apparatus is described comprising a seed layer between a gap layer and an Iridium Manganese (IrMn) antiferromagnetic layer. The seed layer comprises an oxide layer next to a magnetic layer.


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