X-ray absorption studies of the local structure and f-level occupancy in CeIr _1-xRh _xIn ₅

The CeIr _1-xRh _xIn 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≤x≤0.5), specific heat measurements show a broad anomaly, suggestive of gross phase separation. We have performed x-ray absorption experiments at the Ce L _III,Ir L _III, and Rh 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≤x≤0.5 range have some other explanation, and some possibilities are discussed.