Coercivity development from annealing Pt-Co-B melt-spun ribbons

Permanent magnets with coercivity as high as 11.2 kOe have been developed by the melt-spinning processing of Pt-Co-B ternary alloys with subsequent heat treatments. Systematic vacuum annealing of the metastable as-quenched materials has been performed to establish a correlation between the development of coercivity and the evolution of microstructure in order to study the annealing effects on coercivity and magnetic hardening mechanisms. Microstructural characterization shows that the main origin of the increased coercivity is the formation of magnetically anisotropic ordered L1₀ PtCo matrix and the development of single-domain size Co₃B precipitates. This microstructure, which results from annealing the rapidly solidified melt-spun ribbons, limits the magnetic domain nucleation, thus increasing the coercivity