Perminvar effect in binary amorphous CoB alloys

The time-temperature dependent Perminvar effect in amorphous Co(100-x)B(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(sub CR). The fact that H(sub CR) in CoB alloys can be higher than coercive field H(sub C) is rather curious. In the Co75B25 alloy H(sub 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(sub CR) measured at two times t(sub 1) and t(sub 2), a magnetic relaxation spectrum similar to that obtained from reluctivity have been constructed. The kinetics of the H(sub 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.