Study of the Phase Transition from TbCu7 Structure to ThMn12 Structure in Newly Developed ThMn12 Type Magnets Using a Numerical Analysis Method for X-Ray Diffraction Patterns

We developed a new 1-12-type magnetic material of (Sm,Zr)(Fe,Co)11.3Ti0.7 composition that exhibits magnetic properties superior to Nd-Fe-B magnets. In the new 1-12 magnets, the amorphous alloys of above composition show a change in XRD pattern with increasing of heat treatment temperature from a single 1-9 phase to 1-9 and 1-12 mixed phases, and finally to a single 1-12 phase, and the magnetic properties also change accordingly. In this study, we established a method for calculating the formation ratio of the 1-12 phase in the samples from the peak shift of the diffraction peaks of the 1-12 phase base on the peaks of the 1-9 phase. As a result, it was revealed that the formation ratio of the 1-12 phase in the samples, whose XRD pattern of 1-9 and 1-12 mixed phase, has a wide distribution, ranging from about 20 to 80 %. With the development of the phase transition from 1-9 to 1-12 phases, the lattice constant a of 1-12 phase increases, and inversely the lattice constant c of 1-12 phase decreases. Furthermore, it was revealed that the formation ratio of the 1-12 phase was about 83 % for the sample indicating the maximum coercivity Hc = 5.46 kOe.