X-ray absorption studies of the local structure andf-level occupancy inCeIr1−xRhxIn5

Abstract

The ${\mathrm{CeIr}}_{1\ensuremath{-}x}{\mathrm{Rh}}_{x}{\mathrm{In}}_{5}$ series exhibits a range of interesting phenomena, including heavy-fermion superconductivity, non-Fermi liquid behavior, and concomitant antiferromagnetism and superconductivity. In the low-Rh concentration range $(0.1\ensuremath{\leqslant}x\ensuremath{\leqslant}0.5)$, specific heat measurements show a broad anomaly, suggestive of gross phase separation. We have performed x-ray absorption experiments at the $\mathrm{Ce}\phantom{\rule{0.3em}{0ex}}{L}_{\mathrm{III}},\mathrm{Ir}\phantom{\rule{0.3em}{0ex}}{L}_{\mathrm{III}}$, and $\mathrm{Rh}\phantom{\rule{0.3em}{0ex}}K$-edges as a function of Rh concentration and temperature. X-ray absorption near-edge structure measurements indicate that cerium is close to trivalent in this system, with no measurable change with temperature from 20--300 K, consistent with a heavy-fermion material. Extended x-ray absorption fine structure measurements as a function of temperature from all measured edges indicate the local crystal structure of all samples is well ordered, with no gross phase separation observed, even for samples with $x=0.125$ and $x=0.25$. These results therefore suggest that the anomalous specific heat behavior in the $0.1\ensuremath{\leqslant}x\ensuremath{\leqslant}0.5$ range have some other explanation, and some possibilities are discussed.