Structure, phase transformation and magnetic properties of rapidly quenched nanocrystalline Nd-Dy-Fe-Co-Nb-B ribbons

Structure, phase transformation and magnetic properties of melt-spun and annealed (Nd,Dy)(Fe,Co,Nb,B)5.5+x wt.% Fe ribbons with 0⩽x⩽40 have been investigated. It is found that the phase components of the as-quenched alloys are sensitive to the Fe content. Besides the amorphous phase, the Nd2Fe14B-type of phase exists in the as-quenched alloys for x⩾15, and a metastable phase with TbCu7-type of structure coexists with the amorphous and Nd2Fe14B-type phases for x⩾25. After annealing at 700 °C for 10 min, the highest value of 13.1 MGOe is achieved for the maximum energy product, which is due to the exchange coupling between the magnetically soft and hard phases. The metastable 1:7 phase with the TbCu7-type of structure is transformed into Nd2Fe14B-type of phase and α-Fe for the annealing temperatures (Ta) ⩽800 °C, and the 2:17 phase with Th2Zn17-type of structure for Ta⩾900 °C.