Magnetic Aftereffect and Magnetization Reversal of Sr-Ferrite Fine Particles

the magnetic aftereffect constant (S_v), the anisotropy field (H_A) distribution and the rotational hysteresis integral (R_h) were measured for M-type hexagonal strontium ferrite (SrM) fine particles with various average particle diameters (D) and coercive forces (H_cJ). The relations between S_v, the activation volume (v), H_cJ, H_A, and R_h were studied, as well as the effect of milling. S_v is constant and independent of the magnetic field. In S_v varies in proportion to In H_cJ, and the relation H_cJ∝v^-2 was found to obtain in SrM particles not extensively subjected to milling. S_v increases and v decreases for SrM fine particles (D=0.3 μm) whose H_A is widely distributed by milling, even though H_cJ decreases markedly. S_v and v are related to the distribution of H_A. As H_cJ increases, R_h and v decrease, which indicates that the magnetization reversal mechanism of SrM fine particles approaches that of a coherent rotation mode.