Specific heat measurements and structural investigation of CeCu6 - xSnx compounds

International audienceThe evolution of the crystal structure and some magnetic properties of the heavy-fermion material CeCu6 - xSnx (x = 0, 0.25, 0.65, 0.75, 0.85 and 1.0) has been studied by powder neutron diffraction and by specific heat measurements. The substitution of Cu by Sn suppresses the temperature induced orthorhombic to monoclinic transition, known to occur in the pure CeCu6 phase. No structural phase transition has been observed in these samples as a function of x but the cell volume increases considerably in an anisotropic way. Sn occupies preferentially the special Cu crystallographic site which is next to each of the four Ce atoms in the unit cell. The transition to antiferromagnetic order, characterizing the samples with higher x, is sensitive to both x and magnetic field. The results are discussed in the context of the competition between Kondo and RKKY interactions in disordered or not heavy-fermion systems and reveal an interesting interplay between composition, structure and magnetism in CeCu6 - xSnx

Neutron-diffraction study of field-induced transitions in the heavy-fermion compound Ce2RhIn8

We present neutron diffraction measurements in high magnetic fields (0 to 14.5 T) and at low temperatures (2.5, 2.3, 0.77 and 0.068 K) on single crystals of the tetragonal heavy fermion antiferromagnet Ce2RhIn8. For B//[110] the field dependence of selected magnetic and nuclear reflections reveals that the material undergoes several transitions, the temperature dependence of which suggests a complex B-T phase diagram. We present the detailed evolution of the integrated intensities of selected reflections and discuss the associated field-induced transitions.Comment: 12 pages, 3 figures Proceeding Euro-conference "Properties of Condensed Matter probed by x-ray and neutron scattering"; to appear in Physica

A New Heavy-Fermion Superconductor CeIrIn5: Relative of the Cuprates?

CeIrIn5 is a member of a new family of heavy-fermion compounds and has a Sommerfeld specific heat coefficient of 720 mJ/mol-K2. It exhibits a bulk, thermodynamic transition to a superconducting state at Tc=0.40 K, below which the specific heat decreases as T2 to a small residual T-linear value. Surprisingly, the electrical resistivity drops below instrumental resolution at a much higher temperature T0=1.2 K. These behaviors are highly reproducible and field-dependent studies indicate that T0 and Tc arise from the same underlying electronic structure. The layered crystal structure of CeIrIn5 suggests a possible analogy to the cuprates in which spin/charge pair correlations develop well above Tc

Magnetic structure of CeRhIn_5 as a function of pressure and temperature

We report magnetic neutron-diffraction and electrical resistivity studies on single crystals of the heavy-fermion antiferromagnet CeRhIn$_{5}$ at pressures up to 2.3 GPa. These experiments show that the staggered moment of Ce and the incommensurate magnetic structure change weakly with applied pressure up to 1.63 GPa, where resistivity, specific heat and NQR measurements confirm the presence of bulk superconductivity. This work places new constraints on an interpretation of the relationship between antiferromagnetism and unconventional superconductivity in CeRhIn$_{5}$.Comment: 6 pages, 6 figures, submitted to Phys. Rev.

Anomalous NMR Magnetic Shifts in CeCoIn_5

We report ^{115}In and ^{59}Co Nuclear Magnetic Resonance (NMR) measurements in the heavy fermion superconductor CeCoIn_5 above and below T_c. The hyperfine couplings of the In and Co are anisotropic and exhibit dramatic changes below 50K due to changes in the crystal field level populations of the Ce ions. Below T_c the spin susceptibility is suppressed, indicating singlet pairing.Comment: 4 pages, 4 figure

An Experimental and Theoretical Study of the Variation of 4f Hybridization Across the La1-xCexIn3 Series

Crystal structures of a series of La1-xCexIn3 (x = 0.02, 0.2, 0.5, or 0.8) intermetallic compounds have been investigated by both neutron and X-ray diffraction, and their physical properties have been characterized by magnetic susceptibility and specific heat measurements. Our results emphasize atypical atomic displacement parameters (ADP) for the In and the rare-earth sites. Depending on the x value, the In ADP presents either an "ellipsoidal" elongation (La-rich compounds) or a "butterfly-like" distortion (Ce-rich compounds). These deformations have been understood by theoretical techniques based on the band theory and are the result of hybridization between conduction electrons and 4f-electrons.Comment: 7 pages, 8 figure

Thermodynamics and electrodynamics of unusual narrow-gap semiconductors

This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL) that has led to a fully funded DOE program to continue this work. The project was directed toward exploring the Ettingshausen effect, which is the direct extension of the familiar Peltier-effect refrigerator (the process used in popular coolers that run off automotive electrical power) in which a magnetic field is used to enhance refrigeration effects at temperatures well below room temperature. Such refrigeration processes are all-solid-state and are of potentially great commercial importance, but essentially no work has been done since the early 1970s. Using modern experimental and theoretical techniques, the authors have advanced the state-of-the-art significantly, laying the groundwork for commercial cryogenic solid-state refrigeration

Coexistence of magnetism and superconductivity in CeRh1-xIrxIn5

We report a thermodynamic and transport study of the phase diagram of CeRh1-xIrxIn5. Superconductivity is observed over a broad range of doping, 0.3 < x < 1, including a substantial range of concentration (0.3 < x <0.6) over which it coexists with magnetic order (which is observed for 0 < x < 0.6). The anomalous transition to zero resistance that is observed in CeIrIn5 is robust against Rh substitution. In fact, the observed bulk Tc in CeRh0.5Ir0.5In5 is more than double that of CeIrIn5, whereas the zero-resistance transition temperature is relatively unchanged for 0.5 < x < 1