Temperature Dependence of Magnetic Properties in Ferrite Powders by High Energy Ball Milling

Abstract

The ferrite powders were prepared by high energy ball-milling, and subsequently compacted under a pressure of 490MPa for 3min and sintered at 1273~1673K for 3h. The spherical shaped initial powders with a mean size of approximately 70μm were changed to irregular shaped powders of 230nm in a mean size after milling at 300rpm for 3h. The milled powders were composed of the nanosized particles with a size of approximately 10nm. After compacting, the green density was approximately 70%. The sintered sample with a relative density of approximately 98% was obtained by sintering at 1473K, which showed the saturation magnetization (M s ) of approximately 90emu/g and the coercivtity (H c ) of approximately 19Oe at room temperature. The M s decreased with increasing temperature, whereas the H c and initial permeability (μ i ) were unchanged. There was no change in the M s , H c and μ i during holding at 423K.