Crystalline evolution and large coercivity in Dy-doped (Nd,Dy) 2Fe14B/α-Fe nanocomposite magnets
Nanocomposite hard magnetic materials (Nd,Dy)4.5Fe 77.5B18 (No. 1) and (Nd,Dy)4.5Fe 76B18Nb1.2Cu0.3 (No. 2) have been prepared by crystallizing amorphous ribbons, fabricated by single roll melt-spinning. The evolution of a multiphase structure was monitored by an x-ray diffractometer and by thermomagnetic measurement. We observed that, at annealing temperatures below 670 °C, there is crystallization of soft phase Fe3B and a small amount of hard phase Nd2Fe14B. At annealing temperatures above 670 °C, crystallization of α-Fe and probably Dy2Fe14B phases with large magnetocrystalline anisotropy led to a drastic enhancement in the hard magnetic properties of the materials. The maximum value of HC is found to be 4.2 kOe for sample No. 1. For sample No. 2, with co-doping of Nb and Cu, nanostructure refinement yields a strong enhancement in exchange coupling between the component phases. Thereby, we obtained high reduced-remanence of 0.78, high remanence of 1.15 and a high (BH)max value up to 16.2 MGOe. © 2007 IOP Publishing Ltd.