Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-03-21
2004-05-25
Heinz, A. J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06741432
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a current perpendicular to the planes (CPP) spin valve sensor with an in-stack biased free layer and a self-pinned antiparallel (AP) pinned layer structure and, more particularly, to such a sensor with a biasing structure located in the sensor stack and within the track width of the sensor for longitudinally biasing the free layer.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a magnetic disk, a slider that has read and write heads, a suspension arm and an actuator arm that swings the suspension arm to place the read and write heads adjacent selected circular tracks on the disk when the disk is rotating. The suspension arm biases the slider into contact with the surface of the disk or parks it on a ramp when the disk is not rotating but, when the disk rotates and the slider is positioned over the rotating disk, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic field signals to and reading magnetic field signals from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance read head employs a current perpendicular to the planes (CPP) sensor for sensing the magnetic field signals from the rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive or nonconductive layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer typically interfaces the pinned layer for pinning the magnetic moment of the pinned layer 90° to an air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the rotating disk. The sensor is located between ferromagnetic first and second shield layers. First and second leads, which may be the first and second shield layers, are connected to the sensor for conducting a sense current therethrough. The sense current is conducted perpendicular to the major thin film planes (CPP) of the sensor as contrasted to a CIP sensor where the sense current is conducted parallel to the major thin film planes (CIP) of the sensor. A magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic field signals from the rotating magnetic disk. The quiescent position of the magnetic moment of the free layer, which is parallel to the ABS, is when the sense current is conducted through the sensor without magnetic field signals from the rotating magnetic disk.
When the magnetic moments of the pinned and free layers are parallel with respect to one another the resistance of the sensor to the sense current (Is) is at a minimum and when their magnetic moments are antiparallel the resistance of the sensor to the sense current (I
S
) is at a maximum. Changes in resistance of the sensor is a function of cos &thgr;, where &thgr; is the angle between the magnetic moments of the pinned and free layers. When the sense current (I
S
) is conducted through the sensor, resistance changes, due to field signals from the rotating magnetic disk, cause potential changes that are detected and processed as playback signals. The sensitivity of the sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in resistance of the sensor from minimum resistance (magnetic moments of free and pinned layers parallel) to maximum resistance (magnetic moments of the free and pinned layers antiparallel) and R is the resistance of the sensor at minimum resistance.
The first and second shield layers may engage the bottom and the top respectively of the CPP sensor so that the first and second shield layers serve as leads for conducting the sense current (I
S
) through the sensor perpendicular to the major planes of the layers of the sensor. The read gap is the length of the sensor between the first and second shield layers. It should be understood that the thinner the gap length the higher the linear read bit density of the read head. This means that more bits can be read per inch along the track of a rotating magnetic disk which enables an increase in the storage capacity of the magnetic disk drive.
Spin valve sensors are classified as a bottom spin valve sensor or a top spin valve sensor depending upon whether the pinned layer is located near the bottom of the sensor close to the first read gap layer or near the top of the sensor close to the second read gap layer. Spin valve sensors are further classified as simple pinned or antiparallel (AP) pinned depending upon whether the pinned layer structure is one or more ferromagnetic layers with a unidirectional magnetic moment or a pair of ferromagnetic AP layers that are separated by a coupling layer with magnetic moments of the ferromagnetic AP layers being antiparallel. Spin valve sensors are still further classified as single or dual wherein a single spin valve sensor employs only one pinned layer and a dual spin valve sensor employs two pinned layers with the free layer structure located therebetween.
As stated hereinabove, a magnetic moment of the aforementioned pinned layer structure is typically pinned 90° to the ABS by the aforementioned antiferromagnetic (AFM) pinning layer. After forming the sensor, the sensor is subjected to a temperature at or near a blocking temperature of the material of the pinning layer in the presence of a field which is oriented perpendicular to the ABS for the purpose of resetting the orientation of the magnetic spins of the pinning layer. The elevated temperature frees the magnetic spins of the pinning layer so that they align perpendicular to the ABS. This also aligns the magnetic moment of the pinned layer structure perpendicular to the ABS. When the read head is cooled to ambient temperature the magnetic spins of the pinning layer are fixed in the direction perpendicular to the ABS which pins the magnetic moment of the pinned layer structure perpendicular to the ABS. After resetting the pinning layer it is important that subsequent elevated temperatures and extraneous magnetic fields not disturb the setting of the pinning layer.
A scheme for minimizing the aforementioned gap length between the first and second shield layers is to provide a self-pinned AP pinned layer structure. The self-pinned AP pinned layer structure eliminates the need for the aforementioned pinning layer which permits the read gap to be reduced by 120 Å when the pinning layer is platinum manganese (PtMn). In the self-pinned AP pinned layer structure each AP pinned layer has an intrinsic uniaxial anisotropy field and a magnetostriction uniaxial anisotropy field. The intrinisic uniaxial anisotropy field is due to the intrinsic magnetization of the layer and the magnetostriction uniaxial anisotropy field is a product of the magnetostriction of the layer and stress within the layer. A positive magnetostriction of the layer and compressive stress therein results in a magnetostriction uniaxial anisotropy field that can support an intrinsic uniaxial anisotropy field. The orientations of the magnetic moments of the AP pinned layers are set by an external field. This is accomplished without the aforementioned elevated temperature which is required to free the magnetic spins of the pinning layer.
If the self-pinning of the AP pinned layer structure is not sufficient, unwanted extraneous fields can disturb the orientations of the magnetic moments of the AP pinned layers or, in a worst situation, can reverse their directions. Accordingly, there is a strong-felt need to maximize the uniaxial magnetostriction anisotropy field while maintaining a high magnetoresistive coefficient dr/R of the sp
Castro Angel
Heinz A. J.
Johnston Ervin F.
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