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Besnus, M. J., J. P. Kappler, M. F. Ravet, A. Meyer, R. Lahiouel, J. Pierre, E. Siaud, G. L. Nieva, and J. G. Sereni. "Structural and magnetic properties of the ternary rare earth (RE) compound series REInAu2(RE~La to Lu, Y)." Journal of the less-common metals 120, no. 1 (1986): 101–112.
Abstract: Results of structural, magnetic and heat capacity studies are reported for the REInAu2 series (except europium). A crystallographic transformation from cubic to tetragonal structure occurs for the compounds with lanthanum, cerium, praseodymium and neodymium. With the exception of LaInAu2, the phase transition has no observable effect on the magnetic susceptibility. Compounds formed with gadolinium, terbium, dysprosium and holmium order antiferromagnetically at low temperature. In this series YbInAu2 is confirmed to be in an unstable valence state with the maximum 2J + 1 = 8 ground state degeneracy.
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Braun, E., A. Bürger, G. L. Nieva, B. Roden, and J. G. Sereni. "Unexpected magnetic behaviour in a singlet crystal field ground state induced by Tb 4f-instability." Zeitschrift für Physik B Condensed Matter 70, no. 2 (1988): 187–192.
Abstract: The magnetic susceptibility (chi) of Th1-x Tb x alloys (with 5<x<55a/o Tb) in the range of 1 K<T<350K and the specific heat (forx=1.5a/o Tb) for 0.5<T<10 K were measured. A maximum in chi(T) was observed at a temperature which depends on concentration. The crystal field level scheme that fits the specific heat measurements shows two non-magnetic singlets as lowest levels. Such ambiguity is discussed within the framework of the 4f-Tb instability. The results are in agreement with the matrix superconductiveT c decrease. The contribution of the interconfigurational mixing on chi and the specific heat is also discussed.
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NIEVA, G. L., J. G. SERENI, M. AFYOUNI, G. SCHMERBER, and J. P. KAPPLER. "FROM FERROMAGNETIC TO NON-MAGNETIC SINGLET GROUND-STATE IN CEPD1-XNIX." Zeitschrift für Physik B Condensed Matter 70, no. 2 (1988): 181–186.
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Safar, H., P. L. Gammel, D. A. Huse, S. N. Majumdar, L. F. Schneemeyer, D. J. Bishop, D. Lopez, G. L. Nieva, and F. de la Cruz. "Observation of a nonlocal conductivity in the mixed state of YBa2Cu3O7-d: Experimental evidence for a vortex line liquid." Physical Review Letters 72, no. 8 (1994): 1272.
Abstract: We report on transport measurements in the mixed state of YBa2Cu3O7 single crystals using the dc flux transformer geometry. In the vortex fluid regime we have observed the onset of a nonlocal conductivity. At lower temperatures, close to but above the phase transition temperature the vortices become effectively three dimensional in character. This is in sharp contrast to recent flux transformer experiments on Bi2Sr2CaCu2O which have failed to see a nonlocal conductivity, confirming the two-dimensional character at high temperatures of the vortices in that system. These observations suggest that in a finite temperature interval, the vortex state in YBa2Cu3O7 is a line liquid.
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Sereni, J. G., G. L. Nieva, G. Schmerber, and J. P. Kappler. "EVIDENCES FOR UNCONVENTIONAL SUPERCONDUCTIVITY IN RARE-EARTH INTERMETALLICS." Modern Physics Letters B 3, no. 16 (1989): 1225–1231.
Abstract: The specific heat of CeRu2 and La5Rh4 of the superconducting state does not follow a BCS-exponential temperature dependence, but a T2 law. At very low temperature (T = 0.1 Tc), CeRu2 shows a linear T dependence, which corresponds to a constant density of states. The experimental results are well described by the theoretical predictions for an axial state (CeRu2) and polar state (La5Rh4) superconductors. The small Sommerfeld coefficient of La5Rh4(? = 3.4 mJ/K2 La at.) excludes this compound from the heavy fermion superconductors.
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SERENI, J. G., G. L. NIEVA, J. G. HUBER, and L. E. DELONG. "LOW-TEMPERATURE SPECIFIC-HEAT OF THE TH-7(FE,CO,NI)(3) PSEUDOBINARY SUPERCONDUCTORS." PHYSICA C 230, no. 1-2 (1994): 159–162.
Abstract: Low-temperature specific heat (C-p) of the superconducting Th-7(Fe1-xCox)(3) and Th-7(Fe1-xNix)(3) intermetallic compounds is reported. In the normal state, the Sommerfeld coefficient (y), the Debye temperature and the electron-phonon coupling constant are found to be very similar to those of the pure Th. The superconducting phase exhibits a BCS-type behavior, as it is indicated by the exponential Cp vs. T dependence, and the Delta Cp/yT(c), = 1.48 ratio, where Delta Cp is the Cp(T)jump at the transition temperature (T-c).
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Sereni, J. G., G. L. Nieva, G. L. Olcese, A. Herr, and J. P. Kappler. "Ce3In: A cerium concentrated heavy fermion." Physica B: Condensed Matter 171, no. 1-4 (1991): 335–339.
Abstract: The fcc-Ce3In compound is presented as the best available approximation to reproduce the main magnetic properties of gamma-Ce at low temperatures, where such a pure phase does not exist. The electronic specific heat shows a maximum at 18 K and an anomaly at 2.2 K, with an entropy gain of 0.8R ln 4 at 32 K. The susceptibility shows a broad maximum at 1.8 K, while in the magnetization there is no trace of ordering up to 18 T at 1.5 and 4.2 K. We interpret the experimental results as governed by a quadruplet crystal field ground state, which undergoes a quadrupolar transition at 18 K. At lower temperatures a heavy-fermion ground state develops, with C(el)/T = 500 mJ/Ce at. K2 for T --> 0 and CHI-T/C(el) = 0.11 emu K/J for T < 5 K.
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