Tokushichi Mishima, Ryukiti R. Hasiguti and Yasuo Kimura
The magnetic properties of Alnico 5 magnet (8%Al, 14%Ni, 24%Co,3%Cu and Fe) depend sensitively on heat-treatment,that is cooling in magnetic field and subsequent aging. The changes of coercive force, residual induction, maximum energy products and powder patterns of the magnetic domain were observed during these processes. The coercive force (or residual induction) changes logarithmically with the cooling rate. This empirical relationship is satisfied with or without magnetic field when cooling from 1,000 to 700°. The changes of coercive force as a function of aging time after cooling in magnetic field can be expressed by Austin-Rickett's formula. These results are explained qualitatively, if we consider that during cooling in magnetic field the nuclei of meta-stable phase are mainly formed and then the growth process takes place during subsequent aging. In the cooling rate between 0.8 and 7°/sec, the activation energy of subsequent aging process is 46,000 ± 2,000 cal/mol which is independent of the cooling rate.
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