Magnetic Properties of Didymium-Fe-Co-Nb-B Exchange Spring Magnets

Abstract

Amorphous melt-spun ribbons of Didymium-Fe-Co-Nb-B alloys were prepared by the single-roller rapid-quenching method. The effects of the composition, wheel velocity, and heat treatment on the magnetic properties were investigated. Amorphous Didymium₉-Fe₇₆Co₈Nb₁B₆ ribbons prepared at a wheel velocity of 20 m/s were crystallized by heat treatment, and the optimum heat treatment condition was found to be 625°C for 5 min, in which case the value of (BH)_max was 147.3 kJ/m³. The temperature coefficients of B_r and H_cJ for ribbons of crystallized Didymium₉-Fe₇₆Co₈Nb₁B₆ alloy were α(B_r)= -0.087%/°C (reversible) and α(H_cJ)= -0.416%/°C (irreversible), respectively. The value of (BH)_max for a compression molded Didymium₉-Fe₇₆Co₈-Nb₁B₆ isotropic bonded magnet prepared by using the ribbons annealed at 625°C for 5 min was 79.7 kJ/m³.