Magnetic viscosity in strontium ferrite fine particles

The magnetic viscosity coefficient (S/sub v/) and the rotational hysteresis loss (W/sub r/) are measured for M-type hexagonal strontium ferrite (SrM) fine particles whose average diameter (D) and coercive force (H/sub cJ/) differ. The relationship between S/sub v/, H/sub cJ/, the activation volume (v) and W/sub r/ is studied, together with milling effects. This experiment shows that S/sub v/ is constant and independent of the magnetic field. Ln S/sub v/ is in proportion to In H/sub cJ/, and H/sub cJ/ approximately v/sup -2/ could be obtained in SrM fine particles that had less milling effects. It is found that Sv increases and v decreases with SrM fine particles (D=0.3 mu m) whose Wr curve increases in width with milling, even through their H/sub cJ/ significantly decreases. This can be explained as an increase in high magnetic field components of anisotropy field (H/sub A/) caused by milling.>