The Temperature Variation of the Magnetic Viscosity in Ba-ferrite Fine Particles

Abstract

The temperature dependence of the magnetic viscosity coefficient Sv and average anisotropy field HA(ave) were examined for Ba-ferrite fine particles having mean particle volume V of 3.2 × 10-17 cm3, in the temperature range from 200 to 413K. A study was done for the relationship between the activation volume ν calculated based on Sv and average anisotropy constant KA(ave) for Ba-ferrite fine particles. This experiment showed that the temperature dependence of Sv is the same as that of coercive force Hc, and Sv increases with the increase of the temperature. HA(ave) linearly increases as the temperature increases in the temperature range from 293 to 413 K. The activation volume ν is inversely proportional to KA(ave). The values of ν and the critical volume Vc for superparamagnetic behaviour at 293K, are approximately 1.35 × 10-17 and 0.23 × 10-17 cm3, respectively. Larger KA(ave) value is necessary for smaller ν value which is an important factor for high-density magnetic recording. Also, the relations V/ν › 1 and V/Vc ›› 1 are of significant importance.