アモルファス固相からのストロンチウムフェライト微粉末結晶の成長

抄録

Amorphous phases were prepared by the melt spinning method from oxide samples having compositions (S) 41.3 mol%SrO-41.3 mol%Fe₂O₃-17.4 mol%B₂O₃ and (T) 63.1 mol%SrO-19.4 mol%Fe₂O₃-17.5 mol%B₂O₃. When the amorphous phases were crystallized by heat treatment, SrO·6Fe₂O₃ crystal particles precipitated in matrices of unknown phases. The SrO·6Fe₂O₃ particles were extracted by acid-leaching the matrix, and the coercive force of the particles was discussed in terms of the composition of the starting oxide sample and the particle size. The coercive force is strongly dependent on the average particle size. The coercive force reaches 400-560 kA/m at the average particle sizes of 0.05-0.8 and 0.1-0.8 μm in diameter for the SrO·6Fe₂O₃ particles obtained from the samples of compositions S and T, respectively. When the average particle sizes reduce to less than 0.05 μm and 0.1 μm for the particles from samples of compositions S and T, respectively, the coercive forces begin to decrease due to the thermal activation of spins. Also, when the average particle sizes exceed 0.8 μm in both the cases of compositions, the coercive forces begin to decrease. The activation energies (n=7) of the grain growth of the SrO·6Fe₂O₃ particles are 812 and 854 kJ/mol when they precipitate in the amorphous ribbons prepared from samples of compositions S and T, respectively.