Manufacturing process of alnico magnet

Alnico magnets are produced by casting or sintering processes. Anisotropic alnico magnets are oriented by heating above a critical temperature, and cooling in the presence of a magnetic field. Both isotropic and anisotropic alnico require proper heat treatment to develop optimum magnetic properties ¡ª without it alnico's coercivity is about 10 Oe, comparable to technical iron, which is a soft magnetic material. After the heat treatment alnico becomes a composite material, named "precipitation material"¡ªit consists of iron and cobalt rich precipitates in rich-NiAl matrix.

Alnico's anisotropy is oriented along the desired magnetic axis by applying an external magnetic field to it during the precipitate particle nucleation, which occurs when cooling from 900 ¡ãC (1,650 ¡ãF) to 800 ¡ãC (1,470 ¡ãF), near the Curie point. Without an external field there are local anisotropies of different orientations, due to spontaneous magnetization. The precipitate structure is a "barrier" against magnetization changes, as it prefers few magnetization states requiring much energy to get the material into any intermediate state. Also, a weak magnetic field shifts the magnetization of the matrix phase only, and is reversible..

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