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

P J Baker, S R Giblin, F L Pratt, R H Liu, G Wu, X H Chen, M J Pitcher, D R Parker, S J Clarke, S J Blundell
2009 New Journal of Physics  
We report heat capacity measurements of the pnictide materials SmFeAsO_1-xF_x, NdFeAsO, LaFeAsO_1-xF_x and LiFeAs. For SmFeAsO_1-xF_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
more » ... aly, and also show that there is a significant increase in the Sommerfeld coefficient γ 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.
doi:10.1088/1367-2630/11/2/025010 fatcat:efzrz7hamfbgjn4rhktljji2iu