Heat capacity measurements on FeAs-based compounds: a thermodynamic probe of electronic and magnetic states

Abstract

We report heat capacity measurements of the pnictide materials SmFeAsO${}_{1-x}$F${}_x$, NdFeAsO, LaFeAsO${}_{1-x}$F${}_x$ and LiFeAs. For SmFeAsO${}_{1-x}$F${}_x$, with x close to 0.1, we use 3 He measurements to demonstrate a transfer of entropy from the peak at TN to a previously unidentified ~2 K feature which grows with increasing doping. Our results on the Sm samples are compared with a similarly doped La sample to elucidate the crystal field levels of the Sm3+ ion at 0, 23, and 56 meV which lead to a Schottky-like anomaly, and also show that there is a significant increase in the Sommerfeld coefficient $\gamma$ when La is replaced by Sm or Nd. The lattice contribution to the heat capacity of the superconducting oxypnictides is found to vary negligibly with chemical substitution. We also present a heat capacity measurement of LiFeAs showing the feature at Tc, which is significantly rounded and much smaller than the BCS value.

11 pages, 4 figures, submitted to New Journal of Physics focus issue on Iron-Based Superconductors

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Cited by in corpus (1)

• Interplay of Rare Earth and Iron magnetism in RFeAsO with R = La, Ce, Pr, and Sm: A muon spin relaxation study and symmetry analysis