Dual/differential GMR head with a single AFM layer

Details Dual/differential GMR head with a single AFM layer Dual/differential GMR head with a single AFM layer

2001-07-16

2003-12-23

Heinz, A. J. (Department: 2653)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

Reexamination Certificate

active

06667861

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to spin valve magnetoresistive sensors for reading information signals from a magnetic medium and, in particular, to a dual/differential spin valve sensor with a single AFM layer.
2. Description of the Related Art
Computers often include auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (disk drive) incorporating rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces. Magnetic heads including read sensors are then used to read data from the tracks on the disk surfaces.
In high capacity disk drives, magnetoresistive (MR) read sensors, commonly referred to as MR sensors, are the prevailing read sensors because of their capability to read data from a surface of a disk at greater track and linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which an MR element resistance varies as the square of the cosine of the angle between the magnetization in the MR element and the direction of sense current flowing through the MR element. Recorded data can be read from a magnetic medium because the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in the MR element, which in turn causes a change in resistance in the MR element and a corresponding change in the sensed current or voltage.
Another type of MR sensor is the giant magnetoresistance (GMR) sensor manifesting the GMR effect. In GMR sensors, the resistance of the MR sensing layer varies as a function of the spin-dependent transmission of the conduction electrons between magnetic layers separated by a non-magnetic layer (spacer) and the accompanying spin-dependent scattering which takes place at the interface of the magnetic and non-magnetic layers and within the magnetic layers.
GMR sensors using only two layers of ferromagnetic material (e.g., Ni—Fe) separated by a layer of non-magnetic material (e.g., copper) are generally referred to as spin valve (SV) sensors manifesting the SV effect.
FIG. 1
shows a prior art SV sensor
100
comprising end regions
104
and
106
separated by a central region
102
. A first ferromagnetic layer, referred to as a pinned layer
120
, has its magnetization typically fixed (pinned) by exchange coupling with an antiferromagnetic (AFM) layer
125
. The magnetization of a second ferromagnetic layer, referred to as a free layer
110
, is not fixed and is free to rotate in response to the magnetic field from the recorded magnetic medium (the signal field). The free layer
110
is separated from the pinned layer
120
by a nonmagnetic, electrically conducting spacer layer
115
. Hard bias layers
130
and
135
formed in the end regions
104
and
106
, respectively, provide longitudinal bias for the free layer
110
. Leads
140
and
145
formed on hard bias layers
130
and
135
, respectively, provide electrical connections for sensing the resistance of SV sensor
100
. IBM's U.S. Pat. No. 5,206,590 granted to Dieny et al., incorporated herein by reference, discloses a GMR sensor operating on the basis of the SV effect.
Another type of spin valve sensor is an antiparallel (AP) spin valve sensor. The AP-pinned valve sensor differs from the simple simple spin valve sensor in that an AP-pinned structure has multiple thin film layers instead of a single pinned layer. The AP-pinned structure has an antiparallel coupling (APC) layer sandwiched between first and second ferromagnetic pinned layers. The first pinned layer has its magnetization oriented in a first direction by exchange coupling to the antiferromagnetic pinning layer. The second pinned layer is immediately adjacent to the free layer and is antiparallel exchange coupled to the first pinned layer because of the minimal thickness (in the order of 8 Å) of the APC layer between the first and second pinned layers. Accordingly, the magnetization of the second pinned layer is oriented in a second direction that is antiparallel to the direction of the magnetization of the first pinned layer.
The AP-pinned structure is preferred over the single pinned layer because the magnetizations of the first and second pinned layers of the AP-inned structure subtractively combine to provide a net magnetization that is less than the magnetization of the single pinned layer. The direction of the net magnetization is determined by the thicker of the first and second pinned layers. A reduced net magnetization equates to a reduced demagnetization field from the AP-pinned structure. Since the antiferromagnetic exchange coupling is inversely proportional to the net pinning magnetization, this increases exchange coupling between the first pinned layer and the antiferromagnetic pinning layer. The AP-pinned spin valve sensor is described in commonly assigned U.S. Pat. No. 5,465,185 to Heim and Parkin which is incorporated by reference herein.
There is a continuing need to increase the MR coefficient and reduce the thickness of GMR sensors. An increase in the spin valve effect and reduced sensor geometry equates to higher bit density (bits/square inch of the rotating magnetic disk) read by the read head.
SUMMARY OF THE INVENTION
It is an object of the present invention to disclose a dual/differential spin valve sensor having a single AFM layer providing pinning of both a first AP-pinned layer structure and a second simple pinned layer of first and second spin valve structures, respectively.
It is another object of the present invention to disclose a dual/differential spin valve sensor with first and second spin valve structures having oppositely oriented pinned layer magnetization directions.
It is yet another object of the present invention to disclose a dual/differential spin valve sensor with first and second spin valve structures having first and second free layers separated by a distance equal to half the bit length of magnetic data recorded on a magnetic recording media.
It is a further object of the present invention to disclose a dual/differential spin valve sensor having first and second free layers biased to provide 90° relative orientation difference of their magnetizations at the quiescent bias point (i.e. with no signal field present).
In accordance with the principles of the present invention, there is disclosed a dual/differential spin valve sensor comprising a first spin valve structure, a second spin valve stucture and a single antiferromagnetic (AFM) layer disposed between the first and second spin valve structures. The first spin valve structure comprises a first ferromagnetic layer (FM
1
), an AP-pinned layer structure having second and third ferromagnetic layers (FM
2
and FM
3
) separated by an antiparallel coupling (APC) layer, and a conductive first spacer layer disposed between the first and second ferromagnetic layers. The second spin valve structure comprises fourth and fifth ferromagnetic layers (FM
4
and FM
5
) separated by a conductive second spacer layer. The AFM layer is sandwiched between the third and fourth ferromagnetic layers and is exchange coupled to the third and fourth ferromagnetic layers providing an exchange field to pin the magnetization directions of the third and fourth ferromagnetic layers in one direction. Due to the antiferromagetic coupling of the APC layer, the magnetization direction of the second ferromagnetic layer is oriented antiparallel to the magnetization direction of the third ferromagnetic layer. Having an AP-pinned layer for the first spin valve structure and a simple pinned layer for the second spin val

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