Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of biasing or erasing
Reexamination Certificate
2000-03-21
2004-04-27
Hudspeth, David (Department: 2697)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of biasing or erasing
C360S324100
Reexamination Certificate
active
06728055
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to giant magnetoresistive (GMR) heads, and more particularly to a method and apparatus for performing spin valve combined pinned layer reset and hard bias initialization at the HGA level.
2. Description of Related Art
An MR sensor detects magnetic field signals through the resistance changes of a magnetoresistive element, fabricated of a magnetic material, as a function of the strength and direction of magnetic flux being sensed by the element. The conventional MR sensor operates on the basis of the anisotropic magnetoresistive (AMR) effect in which a component of the element resistance varies as the square of the cosine of the angle between the magnetization in the element and the direction of sense or bias current flow through the element.
MR sensors have application in magnetic recording systems because recorded data can be read from a magnetic medium when the external magnetic field from the recorded magnetic medium (the signal field) causes a change in the direction of magnetization in an MR read head. This in turn causes a change in electrical resistance in the MR read head and a corresponding change in the sensed current or voltage.
A different and more pronounced magnetoresistance, called giant magnetoresistance (GMR), has been observed in a variety of magnetic multilayered structures, the essential feature being at least two ferromagnetic metal layers separated by a nonferromagnetic metal layer. This GMR effect has been found in a variety of systems, such as Fe/Cr or Co/Cu multilayers exhibiting strong antiferromagnetic coupling of the ferromagnetic layers, as well as in essentially uncoupled layered structures in which the magnetization orientation in one of the two ferromagnetic layers is fixed or pinned.
A particularly useful application of GMR is a sandwich structure comprising two essentially uncoupled ferromagnetic layers separated by a nonmagnetic metallic spacer layer in which the magnetization of one of the ferromagnetic layers is “pinned”. The pinning may be achieved by depositing the ferromagnetic layer to be pinned onto an antiferromagnetic layer, such as an iron-manganese (Fe—Mn) layer, to create an interfacial exchange coupling between the two layers. The spin structure of the antiferromagnetic layer can be aligned along a desired direction (in the plane of the layer) by heating beyond the “blocking” temperature of the antiferromagnetic layer and cooling in the presence of a magnetic field. The blocking temperature is the temperature at which exchange anisotropy vanishes because the local anisotropy of the antiferromagnetic layer, which decreases with temperature, has become too small to anchor the antiferromagnetic spins to the crystallographic lattice. The unpinned or “free” ferromagnetic layer may also have the magnetization of its extensions (those portions of the free layer on either side of the central active sensing region) also fixed, but in a direction perpendicular to the magnetization of the pinned layer so that only the magnetization of the free-layer central active region is free to rotate in the presence of an external field. The magnetization in the free-layer extensions may be fixed by longitudinal hard biasing or exchange coupling to an antiferromagnetic layer. However, if exchange coupling is used the antiferromagnetic material is different from the antiferromagnetic material used to pin the pinned layer, and is typically nickel-manganese (Ni—Mn). This resulting structure is called a “spin valve” (SV) MR sensor. In a SV sensor only the free ferromagnetic layer is free to rotate in the presence of an external magnetic field. U.S. Pat. No. 5,159,513, assigned to IBM, discloses a SV sensor in which at least one of the ferromagnetic layers is of cobalt or a cobalt alloy, and in which the magnetizations of the two ferromagnetic layers are maintained substantially perpendicular to each other at zero externally applied magnetic field by exchange coupling of the pinned ferromagnetic layer to an antiferromagnetic layer. U.S. Pat. No. 5,206,590, also assigned to IBM, discloses a basic SV sensor wherein the free layer is a continuous film having a central active region and end regions. The end regions of the free layer are exchange biased by exchange coupling to one type of antiferromagnetic material, and the pinned layer is pinned by exchange coupling to a different type of antiferromagnetic material.
Preferably, the thickness of the spacer layer is less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by interfaces between the spacer layer and the pinned and free layers. When the magnetizations of the pinned and free layers are substantially parallel, scattering is minimal and the electrical resistance of the sensor is at a minimum. When the magnetizations of the pinned and free layers are substantially antiparallel, scattering is maximized and the electrical resistance of the sensor is at a maximum. Changes in scattering alter the electrical resistance of the spin valve sensor in proportion to sin &thgr;, where &thgr; is the angle between the magnetizations of the pinned and free layers. A spin valve sensor is characterized by a magnetoresistive (MR) coefficient (the ratio of the change in electrical resistance of the sensor to its maximum electrical resistance) that is substantially higher than the MR coefficient of an anisotropic magnetoresistive (AMR) sensor. For this reason a spin valve sensor is sometimes referred to as a “giant magnetoresistive” (GMR) sensor.
The physical origin is the same in all types of GMR structures: the application of an external magnetic field causes a variation in the relative orientation of the magnetizations of neighboring ferromagnetic layers. This in turn causes a change in the spin-dependent scattering of conduction electrons and thus the electrical resistance of the structure. The resistance of the structure thus changes as the relative alignment of the magnetizations of the ferromagnetic layers changes.
SV sensors are a replacement for conventional MR sensors based on the AMR effect. They have special potential for use as external magnetic field sensors, such as in anti-lock braking systems, and as read heads in magnetic recording systems, such as in rigid disk drives.
A read head employing a spin valve sensor (hereinafter, a “spin valve read head”) may be combined with an inductive write head to form a combined magnetic head. In a magnetic disk drive, an air bearing surface (ABS) of a combined magnetic head is supported adjacent a rotating disk to write information on or read information from the disk. Information is written to the rotating disk by magnetic fields which fringe across a gap between the first and second pole pieces of the write head. In a read mode, the electrical resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields on the rotating disk. When a sense current I
s
is conducted through the spin valve sensor, electrical resistance changes cause potential changes that are detected and processed as playback signals.
Another type of spin valve sensor, an antiparallel (AP) pinned spin valve sensor, is described in commonly assigned U.S. Pat. No. 5,465,185 to Heim and Parkin, which is incorporated into this application by this reference. The AP pinned spin valve sensor differs from the pinned layer spin valve sensor, described above, in that the pinned layer of the AP pinned spin valve sensor comprises multiple thin films, which are collectively referred to as an antiparallel (AP) pinned layer, while the pinned layer of the pinned layer spin valve sensor is a single thin film layer. The AP pinned layer has a nonmagnetic spacer film, hereinafter referred to as an antiparallel (AP) coupling film, sandwiched between first and second ferromagnetic thin films. The first thin film is exchange coupled to the pinning layer by being immediately adjacent thereto, and has its magnetic
Gill Hardayal Singh
Keener Christopher Dana
Patel Gautam Ratilal
Colon Rocio
Crawford & Maunu PLLC
Hudspeth David
International Business Machines - Corporation
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