Kinetics of formation of induced magnetic anisotropy in a zero-magnetostriction amorphous alloy

The kinetics of formation of magnetic annealing anisotropy have been measured in the zero-magnetostriction amorphous alloys (Fe0.063Co0.937)75Si15B10 over the temperature range 165–380 °C by analysis of torque curves on single disk samples. Only at temperatures above 330 °C was it possible to reach equilibrium saturated values of the anisotropy in reasonable times (less than 20 h). By assuming that the equilibrium saturated value of the induced anisotropy is linear with temperature, it is possible to deduce an activation energy for the magnetic annealing process in a well-annealed sample. The value is about 2.0±0.1 eV. This is considerably higher than the value of 1.4 eV found by Luborsky or 1.7 eV reported by Chambron and Chamberod for Fe40Ni40P14B6. The higher value in this work is presumably due to the relatively high glass transition temperature and crystallization temperature of the FeCoBSi alloy. The kinetic data reveal the existence of range or relaxation times, which can be analyzed assuming a log-normal distribution. The width of the distribution of relaxation times β decreases with increasing temperature.