Magnetic properties and crystal field splitting of the rare-earth pyrochlore Er 2 Ir 2 O 7

The effects on the rare-earth crystal-field-splitting schemes of incorporation of large spin-orbit coupling ($5d$) ions, such as ${\\text{Ir}}^{\\text{4}}+$, into the rare-earth pyrochlores are largely unknown. We report on the preparation, specific heat, magnetization, and inelastic neutron-scattering study of ${\\text{Er}}_{\\text{2}}{\\text{Ir}}_{\\text{2}}{\\text{O}}_{\\text{7}}$ pyrochlore. An anomaly in specific heat and bifurcation of zero-field cooled and field cooled magnetization indicates an ordering of the Ir sublattice below 140 K, in good agreement with other rare-earth pyrochlore iridates. The Er sublattice ordering below 2 K can be considered short range as well, following the development of specific-heat and magnetization data down to low temperatures. The inelastic neutron scattering allowed us to unambiguously determine the crystal-field (CF) eigenenergies and parameters of ${\\text{Er}}_{\\text{2}}{\\text{Ir}}_{\\text{2}}{\\text{O}}_{\\text{7}}$, which are dictated dominantly by nearest-neighbor anions (the oxygen cage around the Er cation). The influence of the magnetic iridium cations on the erbium CF scheme is rather moderate despite the strong spin-orbit coupling expected in a $5d$ metal, which is evident when comparing the energy spectra of this iridate and other $3d$- or $4d$-metal containing erbium pyrochlores. The determined CF parameters were subsequently utilized for calculations of magnetization and specific-heat CF contributions, leading to an excellent agreement with experimental data.