Evidence for Different Ferromagnetic Phases in Amorphous Fe40Ni40B20 Detected by EPR

Abstract

Abstract Amorphous ferromagnetic Fe40Ni40B20 (Tc = 662 K) has been investigated by EPR in the temperature range from 110 to 510 K. From the temperature dependence of the magnetic field at resonance, the saturation magnetization could be evaluated. Around 470 K the line width of the resonance signal exhibits a pronounced minimum, and the EPR-intensity deviates at this temperature from pure ferromagnetic behaviour. Both effects can be explained by assuming the presence of a second ferromagnetic phase with a Curie temperature of Tc′=470 K. Upon annealing of Fe40Ni40B20 at temperatures slightly higher than Tc′ changes in physical properties, such as Curie temperature, density and relative strain at fracture are observable. It is proposed that the onset of the low temperature relaxation which is responsible for these changes in physical properties is related to the transition of the second ferromagnetic phase to the paramagnetic state.