Temperature evolution of coercive field and thermal relaxation effects in nanocrystalline FeNbB alloys

Abstract The temperature dependence of the coercive field and thermal magnetic creep at elevated temperatures are studied in nanocrystalline Fe 80.5 Nb 7 B 12.5 . A magnetic hardening near the Curie temperature of the amorphous matrix, T c (am), is followed by a decrease of the coercive field due to the thermal relaxation of the magnetization above T c (am). Our analysis of the logarithmic-like creep above T c (am) reveals activation volumes which are temperature independent and involve many grains. This indicates collective effects mediated by dipolar grain–grain interactions.