Electricity: measuring and testing – Magnetic – Magnetometers
Patent
1997-06-13
1999-02-02
Snow, Walter E.
Electricity: measuring and testing
Magnetic
Magnetometers
338 32R, 360113, 428611, G01R 3309, H01F 100, H01L 4300, G11B 539
Patent
active
058670254
DESCRIPTION:
BRIEF SUMMARY
The present invention relates generally to magnetoresistive sensors, in particular to magnetoresistive sensors based on the so-called "spin-valve" or "giant magnetoresistive (GMR)" effect. The invention further relates to storage systems incorporating such sensors for reading stored information. The magnetoresistive sensor of the present invention is also applicable to any localized measurement task or problem where a magnetic field is to be detected in a restricted volume or area.
BACKGROUND OF THE INVENTION
The prior art discloses a magnetic read transducer referred to as a magnetoresistive (MR) sensor or head which has been shown to be capable of reading data from a magnetic surface at great linear densities. An MR sensor detects magnetic field signals through the resistance changes of a read element fabricated of a magnetic material as a function of the strength and direction of magnetic flux being sensed by the read element. These prior art MR sensors operate on the basis of the anisotropic magnetoresistive (AMR) effect in which a component of the read element resistance varies as the square of the cosine of the angle between the magnetization and the direction of sense current flow through the element. A more detailed description of the AMR effect can be found in "Memory, Storage, and Related Applications", D. A. Thompson et al., IEEE Trans. Mag. MAG-11, p. 1039 (1975).
More recently, a different, more pronounced magnetoresistive effect has been described in which the change in resistance of a layered magnetic sensor is attributed to the spin-dependent transmission of the conduction electrons between the magnetic layers through a non-magnetic layer and the accompanying spin-dependent scattering of electrons at the layer interfaces and within the ferromagnetic layers. This magnetoresistive effect is variously referred to as the "giant magnetoresistive" (GMR) or "spin valve" effect. Such a magnetoresistive sensor fabricated of the appropriate materials provides improved sensitivity and greater change in resistance than observed in sensors utilizing the AMR effect. In this type of MR sensor, the in-plane resistance between a pair of ferromagnetic layers separated by a non-magnetic layer varies as the cosine (cos) of the angle between the magnetization in the two layers.
U.S. Pat. No. 4,949,039 to Grunberg describes a layered magnetic structure which yields enhanced MR effects caused by antiparallel alignment of the magnetizations in the magnetic layers. Grunberg describes the use of antiferromagnetic-type exchange coupling to obtain the antiparallel alignment in which adjacent layers of ferromagnetic materials are separated by a thin interlayer of Cr or Y.
U.S. Pat. No. 5,206,590 to Dieny et al. discloses an MR sensor in which the resistance between two uncoupled ferromagnetic layers is observed to vary as the cosine of the angle between the magnetizations of the two layers. This mechanism produces a magnetoresistance that is based on the spin valve effect and, for selected combinations of materials, is greater in magnitude than the AMR.
The U.S. Pat. No. 5,159,513 to Dieny et al. discloses an MR sensor based on the above-described effect which includes two thin film layers of ferromagnetic material separated by a thin film layer of a non-magnetic metallic material wherein at least one of the ferromagnetic layers is of cobalt or a cobalt alloy. The magnetization of the one ferromagnetic layer is maintained perpendicular to the magnetization of the other ferromagnetic layer at zero externally applied magnetic field by exchange coupling to an antiferromagnetic layer (element 18 in FIG. 2 of U.S. Pat. No. 5,159 513)
Published European Pat. Application EP-A-0 585 009 discloses a spin valve effect sensor in which an antiferromagnetic layer and an adjacent magnetically soft layer co-operate to fix or pin the magnetization of a ferromagnetic layer. The magnetically soft layer enhances the exchange coupling provided by the antiferromagnetic layer.
The spin valve structures described in the above-cited U.S. p
REFERENCES:
patent: 5680091 (1997-10-01), Maeda et al.
Allenspach Rolf
Weber Wolfgang F.
International Business Machines - Corporation
Phillips Steven B.
Snow Walter E.
Woods Gerald R.
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