Crystallization Process of a Ferromagnetic Amorphous Alloy Fe<SUB>77.5</SUB>B<SUB>15</SUB>Si<SUB>7.5</SUB>

The crystallisation process of an amorphous ferromagnet Fe77.5B15Si7.5 has been accurately observed by means of the real time measurement of the magnetic moment which is induced during the course of crystallisation. The experiments made at temperatures between 773 and 733 K have revealed that the crystallisation occurs in two stages with the respective incubation times. The results are well fitted by a modified Johnson-Mehl-Avrami equation, which is improved to take the incubation period and the two-stage crystallisation process into account. Four characteristic periods, the incubation and relaxation times for the two stages, have been obtained by this fitting. The activation energy for each period has a value a little less than 4 eV, which is larger than the activation energies for the ordinary atomic diffusion phenomena. This implies that the atomic diffusion responsible to the crystallisation is not ordinary one but the one which needs extra energy.