High energy NdFeB permanent magnets with nanocrystalline structure

Experimental studies of remanence enhancement and the effect of quenching conditions on rapid solidification of undercooling NdFeB melts with composition near the Nd₂Fe₁₄B phase was investigated by melt spinning technic. Nanocrystalline alloys and nanocomposites Nd₂Fe₁₄B/αFe have been synthesized by melt-spinning a Nd rich alloy, Nd₃₀FeB_0.9 (%weight) and Fe rich alloy Nd_12.6FeB_3.88 (% weight) at the wheel speed in the range up to 25-40 m/s. Microstructural and magnetic studies have showed that is an corresponding rapid solidification and wheel speed for to obtain a uniform nanocrystalline as well amorphous microstructure. Lower speed appearance larger grains for both Nd₂Fe₁₄B and Fe phases, while higher speed leads to appearance of an amorphous phase, which will result in a Nd₂Fe₁₄B/αFe, with lower dimension grains, after subsequent crystallization annealing treatment. Refinement of the mean Nd₂Fe₁₄B crystallites diameter below ~50 nm for melt spun NdFeB alloys leads to enhancement of the remanence above that predicted by Stoner Wohlfarth theory. Increasing the Fe:Nd ratio promotes the formation of nanocomposite Nd₂Fe₁₄B/αFe structure which leads to a further enhancement Jr, owing to interphase, with higher saturation, αFe phase