Influence of rare earth mixing on structural and magnetic properties of Nd2−xErxFe17 compounds

The crystal structure and magnetic properties of mixed rare earth Nd2−xErxFe17 compounds (0 ≤ x ≤ 2.0) were investigated by means of X-ray powder diffraction (XRD) and magnetic measurements. The compounds crystallize in the rhombohedral Th2Zn17-type structure for x ≤ 0.5 and in the hexagonal Th2Ni17-type structure for x = 2.0. Coexistence of the Th2Zn17- and the Th2Ni17-type structures is observed for x = 1.0 and 1.5. Violating the Gibbs' phase rule for a binary system, the linear decrease of the unit-cell volume with the Er concentration persists even in the two-phase region, implying an allotropic character of the coexisting Th2Zn17 and Th2Ni17 phases in the samples with x = 1.0 and 1.5. Thermomagnetic measurements show only one magnetic ordering temperature for the samples in the two-phase region, but temperature dependent XRD reveal obvious magnetovolume effects in both the phases around the magnetic ordering temperature. The saturation magnetization of the compounds exhibits a linear dependence on the Er concentration, indicating an ideal mixing effect of the rare earths on the magnetization in spite of the different crystal structures of the parent compounds.