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 (20)

• Superconductivity in Iron Compounds
• Interplay of Rare Earth and Iron magnetism in RFeAsO with R = La, Ce, Pr, and Sm: A muon spin relaxation study and symmetry analysis
• Superconductivity at 5K in NdO0.5F0.5BiS2
• Quasiparticle relaxation dynamics in spin-density-wave and superconducting SmFeAsO_{1-x}F_{x} single crystals
• Anisotropic Phase Diagram and Superconducting Fluctuations in SmFeAsO0.85F0.15
• Evidence for multiple gaps in specific heat of LiFeAs crystals
• Effect of external pressure on the magnetic properties of LnFeAsO (Ln = La, Ce, Pr, Sm)
• Coupling between 4f and itinerant electrons in SmFeAsO1-xFx (0.15 < x < 0.2) superconductors: an NMR study
• Probing the Ground State Properties of Iron-based Superconducting Pnictides and Related Systems by Muon-Spin Spectroscopy
• Hund's metal crossover and superconductivity in the 111 family of iron-based superconductors
• Structural and physical properties of layered oxy-arsenides LnRuAsO (Ln = La, Nd, Sm, Gd)
• Magneto Seebeck effect in REFeAsO (RE=rare earth) compounds: probing the magnon drag scenario
• Coexistence of magnetism and superconductivity in separate layers of the iron-based superconductor Li_{1-x}Fe_{x}(OH)Fe_{1-y}Se
• Magnetic ordering of the RE lattice in REFeAsO: the odd case of Sm. A specific heat investigation in high magnetic field
• Electronic Behavior of Superconducting SmFeAsO0.75
• Protected Fe valence in quasi-two dimensional $\alpha$-FeSi${}_2$
• Experimental investigation of electronic interactions in collapsed and uncollapsed LaFe2As2 phases
• Direct evidence for the magnetic ordering of Nd ions in NdFeAsO by high resolution inelastic neutron scattering
• Phase transition in CaFeAsH: bridging 1111 and 122 iron-based superconductors
• Complete electronic phase diagram and enhanced superconductivity in fluorine-doped PrFeAsO1-xFx