Grain Growth of Strontium Ferrite Crystallized from Amorphous Phases

Abstract

Amorphous phases have been prepared by melt spinning technique from the oxide samples having compositions 41.3 mol%SrO-41.3 mol%Fe2O3-17.4 mol%B2O3 (composition S) and 63.1 mol%SrO-19.4 mol%Fe2O3-17.5 mol%B2O3(composition T). When these amorphous phases are heat-treated by heat treatment, SrO·6Fe2O3 crystal particles precipitate in multi-phase matrices. The SrO·6Fe2O3 particles were extracted by acid-leaching the matrix, and the coercive forces of the particles are measured in terms of the composition of the starting oxide sample and the particle size. The coercive force depends strongly on the average particle size. The coercive force of the SrO·6Fe2O3 particles reaches 400–560 kA/m (5000–7000 Oe) at the average particle size of 0.05–0.8 and 0.1–0.8 μm for compositions S and T, respectively. When the average particle sizes are reduced to less than 0.05 μm and 0.1 μm for compositions S and T, respectively, the coercive forces begin to decrease due to the thermal activation of spins. Also, when the average particle size exceeds 0.8 μm, the coercive forces begin to decrease for both compositions. The activation energies for the grain growth of the SrO·6Fe2O3 particles are 812 and 854 kJ/mol for compositions S and T, respectively. © 1993, The Japan Institute of Metals. All rights reserved.