Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Utility Patent
1998-09-16
2001-01-02
Evans, Jefferson (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324120
Utility Patent
active
06169647
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to data storage systems. More specifically, the present invention relates to data storage systems using read heads which utilize the giant magnetoresistive (GMR) effect.
Magnetic sensors utilizing the GMR effect, frequently referred to as “spin valve” sensors, are known in the art. A spin valve sensor is typically a sandwiched structure consisting of two ferromagnetic layers separated by a thin non-ferromagnetic layer. One of the ferromagnetic layers is called the “pinned layer” because it is magnetically pinned or oriented in a fixed and unchanging direction by an adjacent anti-ferromagnetic layer, commonly referred to as the “pinning layer,” through anti-ferromagnetic exchange coupling. The other ferromagnetic layer is called the “free” or “unpinned” layer because the magnetization is allowed to rotate in response to the presence of external magnetic fields.
In a giant magnetoresistive sensor, a sense current is applied to the sensor. In the presence of a magnetic field such as that provided by magnetic storage medium, the resistance of the sensor changes resulting in a change in voltage due to the applied sense current. This voltage change may be measured and used to read back information. The operation of one configuration of a GMR sensor is described in U.S. Pat. No. 4,949,039, issued Aug. 14, 1990 to Gr{umlaut over (u)}nberg, entitled “MAGNETIC FIELD SENSOR WITH FERROMAGNETIC THIN LAYERS HAVING MAGNETICALLY ANTIPARALLEL POLARIZED COMPONENTS”.
The signal output from the GMR sensor is due to a change in conductance of the entire device which is dependent upon the relative alignment between the different magnetization vectors in the two ferromagnetic layers (the free layer and the pinned layer). A sufficient exchange coupling field (or pinning field) is required to keep the pinned layer's magnetization direction unchanged during operation of the GMR sensor. The sensitivity of the sensing layer is determined by the effective H
k
of the free layer in the sensor. However, when the stripe height is reduced, the sensitivity of the free layer decreases. One solution to this problem is to use an orthogonal GMR head design such as is described in U.S. Pat. No. 5,696,656 entitled HIGHLY SENSITIVE ORTHOGONAL SPIN VALVE READ HEAD by Gill issued Dec. 9, 1997. In the Gill design, the sense current is directed to flow away from the air bearing surface (ABS) and into the sensor. Since the stripe is now high in this configuration, the demagnetization field is reduced and the sensitivity remains high. However, the metal contact at the air bearing surface significantly reduces the efficiency of the sensor. A complicated flux guide is required in such a design to enhance sensor efficiency and overcome the decrease in sensitivity due to the metal contact.
SUMMARY OF THE INVENTION
A data storage system includes a storage medium having a data surface with data stored thereon, the stored data comprises variations in magnetic fields across the data surface. A slider is adapted to move across the data surface, the slider includes an air bearing surface (ABS) which is substantially parallel to the data surface. A current source provides a sense current (I) and readback circuitry is adapted to receive a readback signal and responsively provide a data output. A magnetoresistive sensor carried on the slider is adapted to receive the sense current (I), readback data from the data surface in response to variations in the magnetic field across the disc surface, and responsively provide the readback signal to the readback circuitry. The sensor is adapted to exhibit a GMR effect in response to a magnetic field. The sensor includes a free layer and a loosely pinned layer. The free layer and the loosely pinned layer each having respective quiescent magnetic field vectors. The magnetic field vectors of the free and loosely pinned layers both rotate in response to an applied magnetic field. In one embodiment, the loosely pinned layer is weakly pinned by an anti-ferromagnetic layer. In another embodiment, two ferromagnetic layers are used having a quiescent bias points which are loosely pinned about 90° apart.
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Hu Shouxiang
Mao Sining
Evans Jefferson
Seagate Technology LLC
Westman Champlin & Kelly P.A.
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