Magnetic materials with exchange anisotropy and process for their manufacture

US3959032A · kind A · utility

Assignee

• BASF SE

Inventors

• Eberhard Koester · Bischofswerda, DE
• Gerd Wunsch · Speyer, DE
• Paul Deigner · Bad Dürkheim, DE
• Dieter Graw
• Karl Uhl
• Werner Steck · Ludwigshafen, DE

Key dates

• Filing date: Dec 23, 1974
• Grant date: May 25, 1976
• Expiry date: Dec 23, 1994

Classification

• Technology area (CPC H): Electricity
• CPC primary: H01F1/0009
• WIPO field: Electrical machinery, apparatus, energy
• WIPO sector: Electrical engineering

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.