The Perminvar effect in binary amorphous CoB alloys

The time-temperature dependent Perminvar effect in amorphous Co _100-xB_x (x=17-30 at%) alloys was investigated in the temperature region of 150 to 450 K for stabilization times of up to 12 hours. After stabilization of the demagnetized domain structure the AC susceptibility (permeability) dependent on the driving magnetic field H shows a constant value up to the Perminvar critical field H_CR . The fact that H_CR in CoB alloys can be higher than coercive field H_C is rather curious. In the Co₇₅B ₂₅ alloy H_CR reaches values of 1.5 to 56 A/m dependent on the time and temperature of the stabilization. From the relative difference between two values of H_CR measured at two times t₁ and t₂ a magnetic relaxation spectrum similar to that obtained from reluctivity have been constructed. The kinetics of the H_CR increase measured at different temperatures indicates that relaxation parameters are equal to those obtained from the magnetic reluctivity aftereffect and that both effects have the same inherent nature