Magnetovolume effect and magnetic properties ofDy2Fe17−xMnx

Abstract

The structural and magnetic properties of ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{17\ensuremath{-}x}{\mathrm{Mn}}_{x}$ $(x=0--5)$ compounds have been investigated using x-ray diffraction, linear thermal expansion, magnetization measurements, and $^{57}\mathrm{Fe}$ M\ossbauer spectroscopy. Compared with ${\mathrm{Dy}}_{2}{\mathrm{Co}}_{17\ensuremath{-}x}{\mathrm{Mn}}_{x}$ 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 ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{17\ensuremath{-}x}{\mathrm{Mn}}_{x}$ 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 $x=1$ [${T}_{C}=370(4)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $x=0.0$, ${T}_{C}=373(4)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $x=1.0$] before decreasing steadily with further increase in Mn content [${T}_{C}=232(4)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{12}{\mathrm{Mn}}_{5}$]. 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 ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{17\ensuremath{-}x}{\mathrm{Mn}}_{x}$ 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 $^{57}\mathrm{Fe}$ hyperfine interaction parameters of the ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{16}{\mathrm{Mn}}_{1}$ and ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{14}{\mathrm{Mn}}_{3}$ samples have been determined from the M\ossbauer spectra $(5--300\phantom{\rule{0.3em}{0ex}}\mathrm{K})$.