Magnetic properties of high coercivity melt-spun didymium-Fe-Co-Nb-V-Tb-B system ribbons and their bonded magnets

The melt-spun ribbons of Didymium_12.5Fe₆₈ Co₁₀ Nb₁V₁Tb_0.5B₇ prepared at a wheel velocity of 17.5 m/s were crystallized by heat treatment. The optimum heat treatment condition was found to be at 600°C for 5 min. The values of (BH)_max and H_cJ amount to 103.6 kJ/m³ and 1628.0 kA/m, respectively. The temperature coefficients of J_r and H_cJ for the crystallized ribbons were α (J_r)_ave=-0.03%/°C (reversible) and α (H_cJ)=-0.37%/°C (irreversible) for the temperature range 25 to 125°C. The compression molded Didymium_12.5Fe₆₈Co₁₀Nb₁V₁Tb_0.5B₇ isotropic bonded magnet, prepared by using the ribbons annealed at 600°C for 5 min, achieve the (BH)_max of 66.2 kJ/m³. The density amounts to 6.32 Mg/m³. At 150°C, irreversible losses of -2.5% result.