Structural and electronic properties of the first iridium containing mixed B-site spinel oxide: Cu [ Ir 1.5 Cu 0.5 ] O 4

Geometrically frustrated systems populated with large spin-orbit coupled ions are an ideal setting for the exploration of novel exotic states of matter. Here we present an example of iridium on a mixed B-site spinel oxide structure: $\mathrm{Cu}[{\mathrm{Ir}}_{1.498(2)}{\mathrm{Cu}}_{0.502(2)}]{\mathrm{O}}_{4}$. Synchrotron XRD refinements reveal a face-centered-cubic structure with space group $Fd\overline{3}m$ and mixed Cu-Ir site disorder within the ${\mathrm{B}}_{2}{\mathrm{O}}_{4}$ rocksalt substructure. Electrical properties reveal a metallic state within the 50--600-K range with a Kondo effect at $Tl50\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. X-ray absorption spectroscopy (XAS) measurements show a mixed ${\mathrm{Cu}}^{1+/2+}$ and ${\mathrm{Ir}}^{3+/4+}$ charge partitioned picture, which suggests a metallic/band description with reduced on-site Coulomb interactions. Spin-glass-like freezing is seen at ${T}_{\mathrm{g}}=49\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and the hysteresis behavior for $Tg{T}_{\mathrm{g}}$ resembles that of a strongly frustrated magnet. DFT calculations show sizable hybridization between the Cu $3d$ and Ir $5d$ states with an effective mixed ${\mathrm{Ir}}^{3+/4+}$ charge partitioned picture, supporting the electronic and XAS results.