Huge magnetic hardening ascribed to metastable crystallites during first stages of devitrification of amorphous FeSiBNbSn alloys

A huge magnetic hardening (i.e., increase of coercivity from 5 A/m up to 4.4 kA/m) was reported for Fe₇₅Si₁₁B₁₀Nb₃Sn alloy ribbons during their very first stage of crystallization from an initial amorphous state. In contrast, Fe₇₈Si₁₁B₁₀Sn₁ showed no such hardening, while a moderate hardening was observed for Fe₇₆Si₁₁B₁₀Nb₃. This outstanding change was ascribed to the generation of metastable nanocrystallites that disappear upon heating at higher temperatures. A noticeable softening was then recovered (with a decrease of coercivity down to 0.8 kA/m) once the optimum homogeneous conventional nanocrystalline phase was achieved. Both structure and magnetic evolutions are followed by different techniques.