Structural and magnetic property evolution of Pr–Fe–Co–B hard magnetic alloys during devitrification annealing

The structural evolution for initially amorphous Prx(Fe0.8Co0.2)94−xB6 (x=12, 10, 9, 8) ribbons during crystallization varies significantly with the Pr content. The amorphous phase in stoichiometric alloy ribbons (x=12) crystallizes directly into Pr2(FeCo)14B. For the x=10 sample, α-(FeCo) forms first, prior to the final equilibrium Pr2(FeCo)14B+α-(FeCo) structure. For the x=9 and 8 ribbons, the structural evolution takes place in three steps with metastable Pr2(FeCo)23B3 phase and 1:7 phases forming as intermediate structures in the x=9 and 8 samples, respectively. In alloy ribbons with x=12, very good second quadrant loop shapes and magnetic property combinations, broadly equivalent to those obtained by directly quenching to the nanocrystalline state, were obtained after optimal annealing. However, for the substoichiometric alloys (x=10, 9, 8), the hysteresis loop shapes and the magnetic properties for optimally annealed ribbons were inferior to their directly quenched counterparts because the grain size for the final 2:14:1/α-Fe structure on annealing was very coarse.