Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-03-29
2001-07-03
Renner, Craig A. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324110, C360S324120
Reexamination Certificate
active
06256178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tunnel junction sensor in a tunnel junction head, and more particularly, to biasing the orientation of the magnetic moment in the free layer in the tunnel junction head using a current field generated by a tunnel current.
2. Description of the Related Art
A read head employing a read sensor 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 the 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 resistance of the read sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a current is conducted through the read sensor, resistance changes cause potential changes that are detected and processed as playback signals in processing circuitry.
One type of read sensor is a tunnel junction sensor. The details of tunnel junction have been described in a commonly assigned U.S. Pat. No. 5,650,958 to Gallagher et al., which is incorporated by reference herein. The tunnel junction sensor is a device comprised of two ferromagnetic layers (i.e., the pinned and free layers) separated by a thin barrier layer and is based on the phenomenon of spin-polarized electron tunneling. The typical tunnel junction sensor uses free and pinned layers, such as NiFe or CoFe, with a non-magnetic barrier layer therebetween that is thin enough to permit quantum mechanical sense current tunneling to occur through the barrier layer between the free and pinned layers. The pinned layer has a magnetic orientation pinned by exchange coupling with a pinning layer wherein the pinning layer is made of antiferromagnetic material with magnetic spins oriented in a predetermined direction. The tunneling phenomenon is electron spin dependent, making the magnetic response of the tunnel junction sensor a function of the relative orientations and spin polarization of the conduction electrons between the free and pinned layers. Ideally, the magnetic moment orientation of the pinned layer should be pinned 90° to the magnetic moment orientation of the free layer, with the magnetic moment of the free layer being free to respond to external magnetic fields such as fields from a rotating magnetic disk. In the absence of any external fields acting on the free layer, the magnetic moment of the free layer is parallel to the direction of the pinned layer, due to a ferromagnetic coupling therebetween.
From the above it becomes apparent that what is needed is a way of biasing the magnetic moment of the free layer such that it is normal to the magnetic moment orientation of the pinned layer in a tunnel junction head in the absence of the external field.
SUMMARY OF THE INVENTION
The present invention is directed to a tunnel junction sensor that employs the field generated from a tunneling sense current through one of the layers to counterbalance a ferromagnetic coupling field exerted on the free layer by the pinned layer. The ferromagnetic coupling field is parallel to the direction of the magnetic moment of a pinned layer. Absent any external forces, the orientation of the magnetic moment of the free layer is unfortunately parallel to the orientation of the magnetic moment of the pinned layer due to their close proximity. For the tunnel junction sensor to work efficiently, the orientation of the magnetic moment of the free layer should be perpendicular to the orientation of the magnetic moment of the pinned layer. To permit a desired orientation of the magnetic moment of the free layer, a tunneling sense current is provided that flows parallel to the ABS in the plane of a conductive layer so as to create a current field antiparallel to the ferromagnetic coupling field. By balancing these two opposed fields, the magnetic moment orientation of the free layer can be perpendicular to the magnetic moment orientation of the pinned layer. To get the tunneling sense current to flow in the plane of the conductive layer, as opposed to through the layer, a non-conducting layer is inserted into the structure. This non-conducting layer makes the current flow in the plane of the desired layer so as to generate the current field of sufficient magnitude to counter balance the ferromagnetic coupling field on the free layer.
In one embodiment, the current flows in the plane of a conductive pinned layer parallel to the ABS so as to create the desired current field. The tunnel junction sensor includes a first shield layer, a non-conductive antiferromagnetic pinning layer with magnetic spins aligned in a predetermined direction, a pinned layer made of conductive ferromagnetic material whose magnetic moment orientation is pinned by exchange coupling with the magnetic spins of the non-conductive antiferromagnetic pinning layer. This magnetization also generates a ferromagnetic coupling field in the predetermined direction. The pinned layer and the first shield are electrically connected in a location remote from the track width area. A non-magnetic barrier layer is positioned between the pinned layer and a free layer. The free layer is made of a ferromagnetic material with a magnetic moment orientation initially parallel to the pinned layer due to the ferromagnetic coupling field. The desired orientation of the free layer is perpendicular to that of the pinned layer magnetic moment orientation (i.e., parallel to the ABS).
In another embodiment, similar to the one described above, a non-conductive insulation layer is placed between the first shield layer and a conductive antiferromagnetic (AFM) pinning layer (which is used in place of the non-conductive pinning layer of the previous embodiment) with magnetic spins aligned in the predetermined direction. The pinning layer and the first shield are electrically connected remote from the track width area. The pinned layer is made of conductive ferromagnetic material whose magnetic moment orientation is pinned by exchange coupling with the conductive antiferromagnetic pinning layer. This magnetization causes the pinned layer to exert a ferromagnetic coupling field on the free layer that is directed perpendicular to the ABS. A non-magnetic barrier layer is positioned between the pinned layer and a free layer. The free layer is made of a ferromagnetic material with a magnetic moment orientation initially parallel to the magnetic orientation of the pinned layer due to the ferromagnetic coupling field. The desired magnetic moment orientation of the free layer is perpendicular to that of the magnetic moment orientation of the pinned layer (i.e., parallel to the ABS).
The first and second shield layers may be used as electrodes for the tunnel junction sensor. A tunneling sense current IT flows through the tunnel junction sensor from the second shield toward the first shield in the track width area, perpendicular to the plane of the films or layers, except the non-conductive layer. As the tunnel current reaches the non-conductive layer, the current turns and flows in the plane of the adjacent conductive layer and parallel to the ABS (either the pinning or pinned layer) and finally to the first shield which is connected to the conductive layer outside of the track width area. As the current flows in the plane of the conductive layer, a tunneling sensor current field is generated antiparallel to the ferromagnetic coupling field. Both of these fields influence the orientation of the magnetic moment of the free layer. By balancing these two fields, the orientation of the magnetic moment of the free layer can be directed perpendicular to the magnetic orientation of the pinned layer. As the tunnel junction sensor is positioned over a rotating magnetic disk, external magnetic fields sensed from the rotating disk moves the orientation of the magnetic moment of the free layer up or down
Gray Cary Ware & Freidenrich
International Business Machines - Corporation
Johnston Ervin F.
Renner Craig A.
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