Magnetovolume effect and magnetic properties of Dy2Fe17-xMnx

The structural and magnetic properties of Dy2Fe17-xMnx (x=0-5) compounds have been investigated using x-ray diffraction, linear thermal expansion, magnetization measurements, and Fe-57 Mossbauer spectroscopy. Compared with Dy2Co17-xMnx compounds for which a linear increase of the unit-cell volume V with increasing Mn fraction is found, the compositional dependence of the lattice parameters of Dy2Fe17-xMnx first exhibits a slight maximum around x=0.5 before increasing monotonically with further increase in x; this behavior can be ascribed to a spontaneous magnetostriction as confirmed by linear-thermal-expansion measurements. The Curie temperature T-C remains essentially unchanged for Mn contents up to x=1 [T-C=370(4) K for x=0.0, T-C=373(4) K for x=1.0] before decreasing steadily with further increase in Mn content [T-C=232(4) K for Dy2Fe12Mn5]. The rapid decrease of spontaneous magnetization and the essentially constant value of T-C for lower Mn concentrations can be understood in terms of the two-sublattice model and by considering the preferential site occupation of Mn atoms in the Dy2Fe17-xMnx unit cell. The exchange interaction between the rare-earth and transition-metal sublattices has been investigated by means of a mean-field analysis of the high-field magnetization isotherms which were measured on the powder samples. The Fe-57 hyperfine interaction parameters of the Dy2Fe16Mn1 and Dy2Fe14Mn3 samples have been determined from the Mossbauer spectra (5-300 K).