Magnetic and Mössbauer Spectral Evidence for the Suppression of the Magnetic Spin Reorientation in Tm₂Fe₁₇ by Deuterium


The structural and magnetic properties of Tm2Fe17 and Tm2Fe17D3.2 are investigated by means of x-ray-diffraction, thermal, and ac magnetic susceptibility measurements, and iron-57 Mössbauer spectroscopy. Both compounds crystallize in a hexagonal P63/mmc space group with a Th2Ni17-like structure. Deuterium insertion into Tm2Fe17 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 Tm2Fe17 in the temperature dependence of both the ac susceptibility and the Mössbauer 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 Mössbauer 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 Mössbauer spectra, deuterium insertion into Tm2Fe17 suppresses this spin reorientation, and in Tm2Fe17D3.2 the iron magnetic moments are oriented within the basal plane of the unit cell from 4.2 to 295 K. The spin reorientation in Tm2Fe17 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 Tm2Fe17 decreases the influence of the thulium anisotropy, and in Tm2Fe17D3.2 the iron anisotropy dominates and favors a basal alignment of the magnetic moments.



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