Magnetic materials with exchange anisotropy and process for thei

Details Magnetic materials with exchange anisotropy and process for thei Magnetic materials with exchange anisotropy and process for thei

1974-12-23

1976-05-25

Kendall, Ralph S.

Metal treatment

Process of modifying or maintaining internal physical...

Magnetic materials

75 5BA, 148 63, 148 3155, 252 6255, H01F 133

Patent

active

039590321

ABSTRACT:
Magnetic materials which essentially consist of a phase A with a ferromagnetic spin system and a phase B with an anti-ferromagnetic spin system, phases A and B interacting by exchange coupling, and the manufacture of such materials. The materials consist essentially of two-phase magnetic single-domain particles, with the alloy [Co.sub.x Ni.sub.1.sub.-x ] as the ferromagnetic phase A and its oxidized form [(CoO).sub.x (NiO).sub.1.sub.-x ] as the anti-ferromagnetic phase B, with values of x of 0.04 to 0.96. They are manufactured by surface oxidation of a pigment layer, which at least covers the surface but may extend deeper, having the composition of phase A, to form an oxide layer, at least 40 A thick, of the phase B, followed by heating in an inert gas atmosphere, or by reduction of a corresponding layer of phase B to a layer of phase A. Magnetic single-domain particles of this composition have a Neel temperature which varies with X. As a result, materials are obtained which have an asymmetrical hysteresis loop, attributable to exchange anisotropy, at temperatures which can be varied within wide limits in accordance with the intended use of the material.

REFERENCES:
patent: 1695041 (1928-12-01), Elmen
patent: 1954102 (1934-04-01), Roseby
patent: 3460968 (1969-08-01), Bate et al.
patent: 3726664 (1973-04-01), Parker et al.

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