Structure and magnetic properties of Er3Fe29-xNbx

A series of Er3Fe29-xNbx compounds (0 <= x <= 1.5) has been synthesized. It is found that although the nominal composition is 3: 29, the compounds crystallize in either the disordered or the ordered Th2Ni17-type structure (space group P6(3)/mmc), except for small amounts of alpha-Fe and ThMn12 (1 : 12) phases as secondary phases, depending on the annealing temperature and Nb content. A tentative phase diagram has been constructed for the Er-Fe-Nb system. Single-phased Er3Fe29-xNbx compounds with the disordered Th2Ni17 structure were obtained at annealing temperatures in the range of 1423-1473 K for x = 0.5-1.2. The structure and magnetic properties of the Er3Fe29-xNbx compounds with the disordered Th2Ni17 structure have been investigated by means of x-ray diffraction and magnetic measurements. It is found that the lattice constants a, c and the unit-cell volume V increase with Nb content. As the Nb content increases the Curie temperature increases and the saturation magnetization M-S decreases. All the compounds have the easy-plane type of anisotropy at room temperature. The temperature dependence of the ac susceptibility shows an anomaly at around 155 K, which may be associated with the temperature-induced domain-wall movement under excitation of the external ac field. The magnetization curves indicate the appearance of a first-order magnetization process (FOMP) and the critical field B-cr of FOMP decreases with increasing Nb content from 5.0 T for x = 0-2.9 T for x = 1.2.