Soft magnetic performance of ultra-rapidly annealed high-Bs Fe-(Co)-B nanocrystalline alloys at elevated temperatures

Abstract

Ultra – rapid annealing (URA) utilizing pair of pre-heated massive Cu blocks has been recently shown to be a useful tool to obtain Fe-(Co)-B based nanocrystalline alloys with reduced metalloid content exhibiting an attractive combination of low coercivity (H c ) and high saturation magnetic induction (B s ) values. However, current knowledge lacks more data about behavior of these alloys at elevated temperatures. In this study we investigate high-temperature performance of the URA annealed (Fe 1−x Co x ) 87 B 13 (x = 0, 0.2, 0.25) nanocrystalline alloys. After annealing for 0.5 s at 763 K, the room temperature coercivities between 6.6 A/m (x = 0) to 10.8 A/m (x = 0.25) and B s values (measured at 8 kA/m) ranging from 1.87 T (x = 0) to 2.01 T (x = 0.2) were attained. The temperature dependence of coercivity was determined from the hysteresis loops measured between room temperature and 573 K. Our experiments revealed that the coercivity of all three alloys firstly decreases with an increase of measuring temperature up to 523 K and then increases. A gradual decrease of the coercivity for T < 523 K was more significant for Fe 87 B 13 alloy, while the abrupt magnetic hardening at 573 K was more significant in the case of Co-containing samples. Possible mechanisms behind the observed high-temperature soft magnetic performance of the studied alloys are discussed. • High temperature soft magnetic behavior was studied in ultra-rapidly annealed Fe-(Co)-B nanocrystalline alloys for the first time. • Continuous decrease of H c with temperature increasing up to 523 K was explained by decreasing magnetoelastic anisotropy. • The addition of cobalt has a beneficial effect on temperature stability of soft magnetic behavior up to 523 K. • Incoherent magnetic anisotropy induced in Fe-Co-B alloys, thermally processed in remanent state below T C is linked to irreversible increase of H c at 573 K.