Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2001-03-08
2003-12-16
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06665155
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spin valve sensor with a free layer structure having a cobalt niobium or cobalt niobium hafnium layer which has a negative magnetostriction for counterbalancing a positive magnetostriction of the remaining of the layers in the free layer structure.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, 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 impressions to and reading magnetic signal fields 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 spin valve sensor for sensing the magnetic signal fields from the rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer structure and a ferromagnetic free layer structure. An antiferromagnetic pinning layer interfaces the pinned layer structure for pinning a magnetic moment of the pinned layer structure 90° to an air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the magnetic disk. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. A magnetic moment of the free layer structure is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or bias point position in response to positive and negative magnetic field signals from a rotating magnetic disk. The quiescent position, which is preferably parallel to the ABS, is the position of the magnetic moment of the free layer structure with the sense current conducted through the sensor in the absence of signal fields.
The thickness of the spacer layer is chosen so that shunting of the sense current and a magnetic coupling between the free and pinned layer structures are minimized. This thickness is typically less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons are scattered at the interfaces of the spacer layer with the pinned and free layer structures. When the magnetic moments of the pinned and free layer structures are parallel with respect to one another scattering is minimal and when their magnetic moments are antiparallel scattering is maximized. Changes in scattering changes the resistance of the spin valve sensor as a function of cos &thgr;, where &thgr; is the angle between the magnetic moments of the pinned and free layer structures. The sensitivity of the sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in the resistance of the sensor as the magnetic moment of the free layer structure rotates from a position parallel with respect to the magnetic moment of the pinned layer structure to an antiparallel position with respect thereto and R is the resistance of the sensor when the magnetic moments are parallel.
In addition to the spin valve sensor the read head includes nonconductive nonmagnetic first and second read gap layers and ferromagnetic first and second shield layers. The spin valve sensor is located between the first and second read gap layers and the first and second read gap layers are located between the first and second shield layers. In the construction of the read head the first shield layer is formed first followed by formation of the first read gap layer, the spin valve sensor, the second read gap layer and the second shield layer. Spin valve sensors are classified as a top or a bottom spin valve sensor depending upon whether the pinning 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 pinned depending upon whether the pinned layer structure is one or more ferromagnetic layers with a unidirectional magnetic moment or a pair of ferromagnetic layers that are separated by a coupling layer with magnetic moments of the ferromagnetic 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.
The free layer structure typically employs a nickel iron layer which provides a desirable magnetic softness for the free layer. This means that the free layer has a low uniaxial anisotropy H
K
which promotes responsiveness of the free layer structure to signal fields from a rotating magnetic disk. When the free layer structure is highly responsive a small signal field will rotate the magnetic moment of the free layer structure which causes a change in the magnetoresistance of the spin valve sensor. It has been found that when the free layer structure also includes a cobalt iron or cobalt layer, sometimes referred to as a nanolayer, between the nickel iron layer and the spacer layer and interfacing the spacer layer that the magnetoresistance or magnetoresistive coefficient dr/R is improved. In order to obtain a desirable increase in the magnetoresistive coefficient dr/R, it has been further found that the thickness of the cobalt iron or cobalt layer should be at least 10Å. Unfortunately, any thickness of the cobalt iron layer reduces the softness of the free layer structure so that it is not as responsive to signal fields from the rotating magnetic disk. A cobalt based film, such as cobalt (Co) or cobalt iron (CoFe), has a magnetic moment of approximately 1.7 times the magnetic moment of nickel iron (NiFe) for a given thickness. Accordingly, an increase in the ratio of the thickness of the cobalt iron or cobalt layer to the thickness of the nickel iron layer increases the uniaxial anisotropy H
K
of the free layer structure and reduces its softness so that it is less responsive to signal fields. Uniaxial anisotropy field is the amount field required to rotate the magnetic moment of the free layer from a position parallel to the ABS to a position perpendicular thereto. One way to overcome the increase in uniaxial anisotropy H
K
of the free layer structure, because of an increase in the thickness of the cobalt iron or cobalt nanolayer, is to increase the thickness of the nickel iron layer so as to reduce the above-mentioned ratio. Unfortunately, this reduces the linear bit density of the read head which is the number of magnetic bits which can be read linearly along a track of a rotating magnetic disk.
Further, any increase in the ratio of the thickness of the cobalt or cobalt iron layer to the thickness of the nickel iron layer causes the free layer structure to have a hysteresis. This hysteresis is indicated in a hysteresis loop which is a graph of the magnetic moment M of the free layer in response to an applied field H (signal field) directed perpendicular to the ABS. The hysteresis loop, which is referred to as the hard axis loop, has an opening due to the hysteresis which can be on the order of 5 to 7 oersteds. The opening in the hard axis loop is quantified as hard axis coercivity H
C
which is measured from the origin of the x and y axes to the intersection of the loop with the x axis (applied signal). It has been found that when the hard axis coercivity is high the
International Business Machines - Corporation
Johnston Ervin F.
Miller Brian E.
LandOfFree
Spin valve sensor with free layer structure having a cobalt... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spin valve sensor with free layer structure having a cobalt..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spin valve sensor with free layer structure having a cobalt... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3112604