Refinement of α-Fe and its improvement on magnetic properties of melt-spun nanocomposite Pr2Fe14B/α-Fe magnets by low wheel speed spinning

Nanocomposite Pr₂Fe₁₄B/α-Fe magnets with uniform microstructure and enhanced magnetic properties have been synthesized by melt-spinning a Pr₈Fe₈₆B₆ alloy at low wheel speed range. Microstructural and magnetic studies showed that there is an optimum wheel speed (about 16.7 m/s) at which a uniform Pr₂Fe₁₄B/α-Fe structure with fine α-Fe grains (about 10 nm) is developed directly from the melt. Lower speed gives larger grains for both the 2:14:1 and α-Fe, while higher speed leads to the appearance of an amorphous phase which will result in a Pr₂Fe₁₄B/α-Fe structure with larger α-Fe grains after a subsequent crystallization annealing. Magnetic properties obtained under the optimum-quenching followed by a subsequent annealing are M_s = 176.6 emu/g, M_r = 118.2 emu/g, M_r/M_s = 0.67, H_c = 5.4 kOe and (BH)_m = 12.6 MGOe. The coercivity and energy product are about 20% higher than those obtained by crystallization of over-quenched samples due to the refinement of α-Fe size which leads to an enhanced exchange coupling between Pr₂Fe₁₄B and α-Fe.