Magnetic and Mössbauer spectral evidence for the suppression of the magnetic spin reorientation inTm2Fe17by deuterium

Abstract

The structural and magnetic properties of ${\mathrm{Tm}}_{2}{\mathrm{Fe}}_{17}$ and ${\mathrm{Tm}}_{2}{\mathrm{Fe}}_{17}{\mathrm{D}}_{3.2}$ are investigated by means of x-ray-diffraction, thermal, and ac magnetic susceptibility measurements, and iron-57 M\ossbauer spectroscopy. Both compounds crystallize in a hexagonal ${P6}_{3}/mmc$ space group with a ${\mathrm{Th}}_{2}{\mathrm{Ni}}_{17}$-like structure. Deuterium insertion into ${\mathrm{Tm}}_{2}{\mathrm{Fe}}_{17}$ induces large increases in the unit-cell volume, the saturation magnetization, and the ordering temperature. The unit-cell expansion is anisotropic, with a larger increase in the a lattice parameter than the c lattice parameter. A spin reorientation is observed at 90 K in ${\mathrm{Tm}}_{2}{\mathrm{Fe}}_{17}$ in the temperature dependence of both the ac susceptibility and the M\ossbauer spectra. Above and below 90 K, the iron magnetic moments are aligned within the basal plane and along the c-axis, respectively. An analysis of the M\ossbauer spectra from 4.2 to 320 K yields the orientation of the iron magnetic moments and hyperfine fields, relative to the axes of the electric-field gradient tensor at the iron sites. As revealed by both the ac susceptibility measurements and the M\ossbauer spectra, deuterium insertion into ${\mathrm{Tm}}_{2}{\mathrm{Fe}}_{17}$ suppresses this spin reorientation, and in ${\mathrm{Tm}}_{2}{\mathrm{Fe}}_{17}{\mathrm{D}}_{3.2}$ the iron magnetic moments are oriented within the basal plane of the unit cell from 4.2 to 295 K. The spin reorientation in ${\mathrm{Tm}}_{2}{\mathrm{Fe}}_{17}$ results from a competition between the thulium and iron magnetic anisotropies. Below 90 K the thulium anisotropy dominates and favors an axial alignment of the spins. In contrast to carbon and nitrogen, deuterium insertion into ${\mathrm{Tm}}_{2}{\mathrm{Fe}}_{17}$ decreases the influence of the thulium anisotropy, and in ${\mathrm{Tm}}_{2}{\mathrm{Fe}}_{17}{\mathrm{D}}_{3.2}$ the iron anisotropy dominates and favors a basal alignment of the magnetic moments.