High-coercivity Nd7.5Y2.7Fe62B22.3Nb3.1Cu2.4 nanocomposite magnet produced by rapid solidification process

Nanocomposite hard magnets in the form of cones have been synthesized by rapid solidification process with Nd7.5Y2.7Fe62B22.3Nb3.1Cu2.4 alloy. X-ray diffraction studies deduced that as-cast alloys have a mixture of α-Fe, Fe3B, Nd2Fe14B and amorphous phase which, upon annealing, transformed into α-Fe, Fe3B and Nd2Fe14B magnetic phases. Transmission electron microscopy and three dimensional atom probe analysis elucidated a nanocrystalline microstructure consists of magnetically soft α-Fe, Fe3B and hard Nd2Fe14B nanograins. The good hard magnetic properties such as remanence (Br) of 0.45 T, coercivity (iHc) of 1315 kA/m and maximum energy product (BH)max of 56.7 kJ/m3 were obtained after annealing the Nd7.5Y2.7Fe62B22.3Nb3.1Cu2.4 alloy at 1013 K for 15 min. Henkel plot yielded the existence of strong inter-grain exchange interactions between magnetically soft and hard grains. High coercivity of 1315 kA/m for the optimally annealed Nd7.5Y2.7Fe62B22.3Nb3.1Cu2.4 alloy is ascribed to the large volume fraction of hard magnetic phase, high magnetocrystalline anisotropy and interface effects.