Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-03-30
2002-06-04
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06400536
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a low uniaxial anisotropy cobalt iron (CoFe) free layer structure for giant magnetoresistive (GMR) and tunnel junction heads and, more particularly, to a multilayered free layer structure wherein the uniaxial anisotropies (H
K
) of the layers counterbalance one another to provide a low net uniaxial anisotropy.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly mounted on a slider that has an air bearing surface (ABS). 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 the 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 impressions 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.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a nomnagnetic gap layer at an air bearing surface (ABS) of the write head. The pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field into the pole pieces that fringes across the gap between the pole pieces at the ABS. The fringe field or the lack thereof writes information in tracks on moving media, such as in circular tracks on a rotating disk.
In recent read heads a spin valve sensor is employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer, and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to an air bearing surface (ABS) of the head and the magnetic moment of the free layer is located parallel to the ABS but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layers are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos &thgr;, where &thgr; is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor resistance changes cause potential changes that are detected and processed as playback signals by the processing circuitry.
The spin valve sensor is characterized by a magnetoresistive (MR) coefficient that is substantially higher than the MR coefficient of an anisotropic magnetoresistive (AMR) sensor. MR coefficient is dr/R were dr is the change in resistance of the spin valve sensor and R is the resistance of the spin valve sensor before the change. A spin valve sensor is typically referred to as a giant magnetoresistive (GMR) sensor. When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve.
Another type of spin valve sensor is an antiparallel (AP) spin valve sensor. The AP pinned spin valve sensor differs from the simple spin valve sensor in that the AP pinned spin valve sensor has an AP pinned structure that has first and second AP pinned layers instead of a single pinned layer. An AP coupling layer is sandwiched between the first and second AP pinned layers. The first AP pinned layer has its magnetic moment oriented in a first direction by exchange coupling to the antiferromagnetic pinning layer. The second AP pinned layer is immediately adjacent to the free layer and is antiparallel exchange coupled to the first AP pinned layer because of the minimal thickness (in the order of 8 Å) of the AP coupling layer between the first and second AP pinned layers. Accordingly, the magnetic moment of the second AP pinned layer is oriented in a second direction that is antiparallel to the direction of the magnetic moment of the first AP pinned layer.
Another type of read sensor is a tunnel junction sensor. The details of tunnel junction are described in a commonly assigned U.S. Pat. No. 5,650,958 to Gallagher et al., which is incorporated by reference herein. A typical tunnel junction sensor has two ferromagnetic layers (i.e., the pinned and free layers) separated by a thin spacer layer which relies upon the phenomenon of spin-polarized electron tunneling. The free and pinned layers, which may be NiFe or CoFe, are crystalline in structure and are separated by an electrically insulating spacer layer that is thin enough that quantum mechanical tunneling occurs between the free and pinned layers. 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 direction of the free layer being able to respond to external magnetic fields. The pinned layer has a magnetic moment that is pinned in its orientation by exchange coupling with a pinning layer that is made of an antiferromagnetic material.
In each of the GMR sensor and the tunnel junction sensor it has been found that a thin layer of cobalt (Co), and preferably cobalt iron (CoFe), between the free layer and the spacer layer increases the magnetoresistive coefficient (dr/R) of the sensor. For purposes to be explained hereinafter the thickness of the cobalt (Co) or cobalt iron (CoFe) layer is very thin, such as 10 Å, and for this reason it is sometimes referred to as a nanolayer. The nanolayer is exchange coupled to the free layer, which is typically nickel iron (NiFe). The nickel iron (NiFe) and the nanolayer are considered collectively as the free layer. Because of their exchange coupling each layer has a magnetic moment that is oriented in the same direction. This direction is parallel to the ABS in a quiescent state, namely when the sensor is not subjected to an applied field (H) from the rotating magnetic disk.
Each of the nanolayer and the nickel iron (NiFe) layer has a uniaxial anisotropy (H
K
). Uniaxial anisotropy is the amount of applied field (H) that is required to rotate the magnetic moment of the layer from an easy axis position to 90° thereto. In the case of a free layer it would be the amount of applied field (H) from the rotating magnetic disk required to rotate the magnetic moment of the free layer from a position parallel to the ABS to a position perpendicular to the AB
Gray Cary Ware & Freidenrich
Johnston Ervin F.
Miller Brian E.
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