Copper alloy GMR recording head

Details Copper alloy GMR recording head Copper alloy GMR recording head

2000-03-20

2002-12-17

Ometz, David L. (Department: 2651)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

Reexamination Certificate

active

06496337

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to the general field of magnetic disk systems with particular reference to very thin GMR based read heads
BACKGROUND OF THE INVENTION
Read-write heads for magnetic disk systems have undergone substantial development during the last few years. In particular, older systems in which a single device was used for both reading and writing, have given way to configurations in which the two functions are performed by different structures. An example of such a read-write head is schematically illustrated in FIG.
1
. The magnetic field that ‘writes’ a bit at the surface of recording medium
15
is generated by a flat coil, two of whose windings
14
can be seen in the figure. The magnetic flux generated by the flat coil is concentrated within pole pieces
12
and
13
which, while being connected at a point beyond the top edge of the figure, are separated by small gap
16
. Thus, most of the magnetic flux generated by the flat coil passes across this gap with fringing fields extending out for a short distance where the field is still powerful enough to magnetize a small portion of recoding medium
15
.
The present invention is directed towards the design of read element
20
which can be seen to be a thin slice of material located between magnetic shields
11
and
12
(
12
doing double duty as a pole piece, as just discussed). The principle governing the operation of read sensor
20
is the change of resistivity of certain materials in the presence of a magnetic field (magneto-resistance). Most magnetic materials exhibit anisotropic behavior in that they have a preferred direction along which they are most easily magnetized (known as the easy axis). The magneto-resistance effect manifests itself as a decrease in resistivity when the material is magnetized in a direction perpendicular to the easy axis, said decrease being reduced to zero when magnetization is along the easy axis. Thus, any magnetic field that changes the direction of magnetization in a magneto-resistive material can be detected as a change in resistance.
It is widely known that the magneto-resistance effect can be significantly increased by means of a structure known as a spin valve. The resulting increase (known as Giant magneto-resistance or GMR) derives from the fact that electrons in a magnetized solid are subject to significantly less scattering by the lattice when their own magnetization vectors (due to spin) are parallel (as opposed to anti-parallel) to the direction of magnetization of the solid as a whole.
The key elements of a spin valve structure are shown in FIG.
2
. In addition to a seed layer
22
on a substrate
21
and a topmost cap layer
27
, these key elements are two magnetic layers
23
and
25
, separated by a non-magnetic layer
24
. The thickness of layer
24
is chosen so that layers
23
and
25
are sufficiently far apart for exchange effects to be negligible (the layers do not influence each other's magnetic behavior at the atomic level) but are close enough to be within the mean free path of conduction electrons in the material. If, now, layers
23
and
25
are magnetized in opposite directions and a current is passed though them along the direction of magnetization (such as direction
28
in the figure), half the electrons in each layer will be subject to increased scattering while half will be unaffected (to a first approximation). Furthermore, only the unaffected electrons will have mean free paths long enough for them to have a high probability of crossing over from
23
to
25
(or vice versa). However, once these electrons ‘switch sides’, they are immediately subject to increased scattering, thereby becoming unlikely to return to their original side, the overall result being a significant increase in the resistance of the entire structure.
In order to make use of the GMR effect, the direction of magnetization of one the layers
23
and
25
is permanently fixed, or pinned. In
FIG. 2
it is layer
25
that is pinned. Pinning is achieved by first magnetizing the layer (by depositing and/or annealing it in the presence of a magnetic field) and then permanently maintaining the magnetization by over coating with a layer of antiferromagnetic material, or AFM, (layer
26
in the figure). Layer
23
, by contrast, is a “free layer” whose direction of magnetization can be readily changed by an external field (such as that associated with a bit at the surface
15
of a magnetic disk).
The structure shown in
FIG. 2
is referred to as a top spin valve because the pinned layer is at the top. It is also possible to form a ‘bottom spin valve’ structure where the pinned layer is deposited first (immediately after the seed and pinning layers). In that case the cap layer would, of course, be over the free layer.
A routine search of the prior art was conducted. While several references to various laminated structures within spin valves were encountered, none of these teach how the GMR ratio may be maintained at a high value while at the same time reducing the overall thickness of the structure. Several of the references found were, however, of interest. For example, Fontana, Jr. et al. (U.S. Pat. No. 5,701,223) forms a pinned layer by strongly coupling two ferromagnetic films in an antiferromagnetic configuration i.e. the two films have a relative antiparallel orientation. The magnetic moments of the two ferromagnetic layers are required to be almost the same. Under these conditions, a pinning layer of nickel oxide may be used and this has the advantage that a cap layer is no longer needed.
In U.S. Pat. No. 5,920,446, Gill describes a laminated free layer formed from two ferromagnetic layers separated by a non-magnetic, conducting spacer layer. A key feature is that the two outer layers of the laminate are coupled in an anti-parallel configuration. This arrangement allows the device to operate without a pinned (or pinning) layer.
In U.S. Pat. No. 5,790,351, Suzuki describes a magnetoresistive head in which longitudinal bias is supplied through a film positioned to be on either side of the magnetoresistive element, this sub-structure lying on a ground plane of copper.
SUMMARY OF THE INVENTION
It has been an object of the present invention to provide a spin valve structure that is both thinner than prior art structures as well as having a good GMR ratio.
Another object of the invention has been to enhance the magnetic-anisotropy of a GMR free layer made up of only CoFe or COFeX.
A further object of the invention has been to provide a process for manufacturing said spin valve structure.
These objects have been achieved by inserting a seed enhancement layer between the seed and the free layer. This seed enhancement layer must have a FCC crystal structure. Our preferred material for it has been NiCu. When this layer is present, a constant GMR ratio of about 7% is obtained for a thickness range of the free layer of from 10 to 40 angstroms. A process for manufacturing this structure is also disclosed.


REFERENCES:
patent: 5637235 (1997-06-01), Kim et al.
patent: 5701223 (1997-12-01), Fontana, Jr. et al.
patent: 5790351 (1998-08-01), Suzuki
patent: 5850323 (1998-12-01), Kanai
patent: 5898548 (1999-04-01), Dill et al.
patent: 5920446 (1999-07-01), Gill
patent: 6046892 (2000-04-01), Aoshima et al.
patent: 6175477 (2001-01-01), Lin et al.
patent: 6201671 (2001-03-01), Pinarbasi
patent: 6208492 (2001-03-01), Pinarbasi
patent: 6219208 (2001-04-01), Gill
patent: 6222707 (2001-04-01), Huai et al.
patent: 6275362 (2001-08-01), Pinarbasi
patent: 6278592 (2001-08-01), Xue et al.
patent: 6292336 (2001-09-01), Horng et al.

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