Complex transport and magnetism in inhomogeneous mixed valence Ce 3 Ir 4 Ge 13

We report the discovery of ${\mathrm{Ce}}_{3}{\mathrm{Ir}}_{4}{\mathrm{Ge}}_{13}$, a Remeika phase with a complex array of structural, electronic, and magnetic properties. Our single crystal x-ray diffraction measurements show that ${\mathrm{Ce}}_{3}{\mathrm{Ir}}_{4}{\mathrm{Ge}}_{13}$ forms in the tetragonally distorted $I{4}_{1}/amd$ space group, which has three distinct rare earth sites. The electrical resistivity is almost temperature independent over three decades in temperature, from 0.4 K to 400 K, while the Hall coefficient measurements are consistent with a low-carrier semimetal. Magnetic susceptibility measurements reveal an effective moment, ${\ensuremath{\mu}}_{\mathrm{eff}}^{\mathrm{exp}}=1.87{\ensuremath{\mu}}_{B}/\mathrm{Ce}$, that falls significantly short of the expected value for ${\mathrm{Ce}}^{3+}$, suggesting that two of the rare earth sites are occupied by magnetic ${\mathrm{Ce}}^{3+}$ while the third is occupied by nonmagnetic ${\mathrm{Ce}}^{4+}$. Upon cooling, ${\mathrm{Ce}}_{3}{\mathrm{Ir}}_{4}{\mathrm{Ge}}_{13}$ first enters a short range magnetically ordered state below ${T}_{\text{SRO}}=10\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, marked by a deviation from Curie-Weiss behavior in susceptibility and a broad field-independent heat capacity anomaly. At lower temperatures, we observe a second, sharper peak in the heat capacity at ${T}^{*}=1.7\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, concurrent with a splitting of the field-cooled and zero-field-cooled susceptibilities. A small resistivity drop at ${T}^{*}$ suggests a loss of spin disorder scattering consistent with a magnetic ordering or spin freezing transition. ${\mathrm{Ce}}_{3}{\mathrm{Ir}}_{4}{\mathrm{Ge}}_{13}$ is therefore a rare example of an inhomogeneous mixed valence compound with a complex array of thermodynamic and transport properties.