Abstract
The newly synthesized ${\mathrm{Tm}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ iridate is investigated using neutron scattering techniques. Powder neutron diffraction patterns confirm that ${\mathrm{Tm}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ crystallizes in a cubic structure of pyrochlore type, consistent with the rest of the rare-earth ${A}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ series, and the crystal structure is preserved down to 0.2 K. The thermal expansion of the crystal lattice is well described by a Debye model of lattice vibrations. A weak magnetic signal consistent with the so-called all-in-all-out magnetic order (AIAO) is traced at low temperature; however, it cannot serve as unambiguous evidence of the AIAO structure in the compound. Nondispersive magnetic excitations in energy-momentum space are observed in inelastic neutron scattering spectra of ${\mathrm{Tm}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$. The crystal-field scheme and parameters of the thulium iridate are refined and discussed with respect to the specific heat and magnetization data. The results are supported by mean-field calculations.
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