Dual GMR sensor with a single AFM layer

Details Dual GMR sensor with a single AFM layer Dual GMR sensor with a single AFM layer

1999-03-30

2001-08-21

Renner, Craig A. (Department: 2652)

Dynamic magnetic information storage or retrieval

Head

Magnetoresistive reproducing head

Reexamination Certificate

active

06278589

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dual GMR sensor with a single AFM layer and, more particularity, to a dual GMR sensor that has a thinner sensor stack and wherein spin valve effects of first and second GMR sensors are additive to improve the GMR output.
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 nonmagnetic 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.
The read head includes a sensor that is located between nonmagnetic electrically insulative first and second read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. 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 pinning 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 sometimes 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 an AP pinned structure has multiple thin film layers instead of a single pinned layer. The AP pinned structure has an AP coupling layer sandwiched between first and second ferromagnetic pinned layers. The first pinned layer has its magnetic moment oriented in a first direction by exchange coupling to the antiferromagnetic pinning layer. The second pinned layer is immediately adjacent to the free layer and is antiparallel exchange coupled to the first pinned layer because of the minimal thickness (in the order of 8 Å) of the AP coupling film between the first and second pinned layers. Accordingly, the magnetic moment of the second pinned layer is oriented in a second direction that is antiparallel to the direction of the magnetic moment of the first pinned layer.
The AP pinned structure is preferred over the single pinned layer because the magnetic moments of the first and second pinned layers of the AP pinned structure subtractively combine to provide a net magnetic moment that is less than the magnetic moment of the single pinned layer. The direction of the net moment is determined by the thicker of the first and second pinned layers. A reduced net magnetic moment equates to a reduced demagnetization (demag) field from the AP pinned structure. Since the antiferromagnetic exchange coupling is inversely proportional to the net pinning moment, this increases exchange coupling between the first pinned layer and the pinning layer. The AP pinned spin valve sensor is described in commonly assigned U.S. Pat. No. 5,465,185 to Heim and Parkin which is incorporated by reference herein.
Efforts continue to increase the MR coefficient (dr/R) of GMR heads. An increase in the spin valve effect equates to higher bit density (bits/square inch of the rotating magnetic disk) read by the read head.
SUMMARY OF THE INVENTION
I first investigated a dual GMR sensor wherein each GMR sensor had a respective antiferromagnetic (AFM) pinning layer. This dual GMR sensor included a ferromagnetic free layer that is located between nonmagnetic electrically conductive first and second spacer layers, the first and second spacer layers being located between ferromagnetic first and second pinned layers and the first and second pinned layers being located between first and second antiferromagnetic (AFM) pinning layers. A typical thickness of each antiferromagnetic pinning layer is equal to or greater than 250 Å. A sought for total gap length (distance between the first and second shield layers) is about 1000 Å. Accordingly, the two antiferromagnetic pinning layers consume about one-half of the sought for total gap length. With the thicknesses of the other layers of the dual GMR sensor added to the thicknesses of the two ferromagnetic pinning layers, the first and second read gap layers must be very thin in order to maintain a thickness of 1000 Å. The thin first and second read gap layers significantly increase the probability of electrical shorts between the sensor and the first and second shield layers. When the first and second pinned layers are antiparallel (AP) pinned layers, as discussed hereinabove, the overall thickness of each AP pinned layer further contributes to reducing the thickness of the first and second read gap layers. As stated hereinabove, the AP pinned layer is mor

Affiliated with

Also associated with

Rating

Dual GMR sensor with a single AFM layer does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Dual GMR sensor with a single AFM layer, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dual GMR sensor with a single AFM layer will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2435184