Neutron scattering study of the Tm2Ir2O7 pyrochlore iridate

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.