Specific Heat of Ce(1-x)La(x)RhIn(5) in Zero and Applied Magnetic Field: A Very Rich Phase Diagram

We report specific-heat results on a single crystal as well as some polycrystalline samples of Ce 1 - x La x RhIn 5 . Determination of the magnitude of the specific heat y (≡C/T as T→0) as a function of concentration is madesomewhat uncertain by the structure of the specific heat below 3 K. However, within our error bar, this y (≤100 mJ/Ce-mol K 2 )-which differs by approximately a factor of 4 with previous estimates-seems consistent with the effective masses observed in recent de Haas-van Alphen measurements. We find, in addition, that (a) there exists a field-induced transition for x≥0.5 that increases in temperature with increasing applied magnetic field and (b) although single and polycrystalline materials give approximately the same specific heat for x=0.15 and 0.95, the second phase (removable via long-term annealing) in the polycrystalline material plays a role for x=0.5 and 0.8. Furthermore, the low-temperature specific heat shows an upturn in C/T at low temperature for x≥0.5 in both single-crystal and polycrystalline materials, which appears to be intrinsic. The field-induced anomaly, coupled with both the temperature and field dependence of the magnetization data and the temperature dependence of this low-temperature upturn in the zero field C/T (proportional to T - 1 + λ ) may be evidence for the Griffiths phase non-Fermi-liquid behavior due to the inherent disorder of doped samples.