464 research outputs found

    Magnetic Transition in the Kondo Lattice System CeRhSn2

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    Our resistivity, magnetoresistance, magnetization and specific heat data provide unambiguous evidence that CeRhSn2 is a Kondo lattice system which undergoes magnetic transition below 4 K.Comment: 3 pages text and 5 figure

    Muon Spin Relaxation Studies of Superconductivity in a Crystalline Array of Weakly Coupled Metal Nanoparticles

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    We report Muon Spin Relaxation studies in weak transverse fields of the superconductivity in the metal cluster compound, Ga_84\_{84}[N(SiMe_3\_{3})_2\_{2}]_20\_{20}-Li_6\_{6}Br_2\_{2}(thf)_20⋅\_{20}\cdot 2toluene. The temperature and field dependence of the muon spin relaxation rate and Knight shift clearly evidence type II bulk superconductivity below T_c≈7.8T\_{\text{c}}\approx7.8 K, with B_c1≈0.06B\_{\text{c1}}\approx 0.06 T, B_c2≈0.26B\_{\text{c2}}\approx 0.26 T, κ∼2\kappa\sim 2 and weak flux pinning. The data are well described by the s-wave BCS model with weak electron-phonon coupling in the clean limit. A qualitative explanation for the conduction mechanism in this novel type of narrow band superconductor is presented.Comment: 4 figures, 5 page

    Proximity effects in the superconductor / heavy fermion bilayer system Nb / CeCu_6

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    We have investigated the proximity effect between a superconductor (Nb) and a 'Heavy Fermion' system (CeCu_6) by measuring critical temperatures TcT_c and parallel critical fields H_{c2}^{\parallel}(T) of Nb films with varying thickness deposited on 75 nm thick films of CeCu_6, and comparing the results with the behavior of similar films deposited on the normal metal Cu. For Nb on CeCu_6 we find a strong decrease of T_c with decreasing Nb thickness and a finite critical thickness of the order of 10 nm. Also, dimensional crossovers in H_{c2}^{\parallel}(T) are completely absent, in strong contrast with Nb/Cu. Analysis of the data by a proximity effect model based on the Takahashi-Tachiki theory shows that the data can be explained by taking into account both the high effective mass (or low electronic diffusion constant), {\it and} the large density of states at the Fermi energy which characterize the Heavy Fermion metal.Comment: 7 pages, 2 figure. Manuscript has been submitted to a refereed journa

    Magnetism of PdNi alloys near the critical concentration for ferromagnetism

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    We report results of a muon spin rotation and relaxation (μ\muSR) study of dilute Pd1−x_{1-x}Nix_x alloys, with emphasis on Ni concentrations x=x = 0.0243 and 0.025. These are close to the critical value xcrx_\mathrm{cr} for the onset of ferromagnetic long-range order (LRO), which is a candidate for a quantum critical point. The 2.43 and 2.5 at.% Ni alloys exhibit similar μ\muSR properties. Both samples are fully magnetic, with average muon local fields ⟨Bloc⟩=\langle B^\mathrm{loc}\rangle = 2.0 and 3.8 mT and Curie temperatures TC=T_C = 1.0 and 2.03 K for 2.43 and 2.5 at.% Ni, respectively, at T=0T = 0. The temperature dependence of ⟨Bloc⟩\langle B^\mathrm{loc}\rangle suggests ordering of Ni spin clusters rather than isolated spins. Just above TCT_C a two-phase region is found with separate volume fractions of quasistatic short-range order (SRO) and paramagnetism. The SRO fraction decreases to zero with increasing temperature a few kelvin above TCT_C. This mixture of SRO and paramagnetism is consistent with the notion of an inhomogeneous alloy with Ni clustering. The measured values of TCT_C extrapolate to xcrx_\mathrm{cr} = 0.0236 ±\pm 0.0027. The dynamic muon spin relaxation in the vicinity of TCT_C differs for the two samples: a relaxation-rate maximum at TCT_C is observed for xx = 0.0243, reminiscent of critical slowing down, whereas for x=x = 0.025 no dynamic relaxation is observed within the μ\muSR time window. The data suggest a mean-field-like transition in this alloy.Comment: 15 pages, 15 figures, to be published in Phys. Rev.

    Evolution of Quantum Criticality in CeNi_{9-x}Cu_xGe_4

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    Crystal structure, specific heat, thermal expansion, magnetic susceptibility and electrical resistivity studies of the heavy fermion system CeNi_{9-x}Cu_xGe_4 (0 <= x <= 1) reveal a continuous tuning of the ground state by Ni/Cu substitution from an effectively fourfold degenerate non-magnetic Kondo ground state of CeNi_9Ge_4 (with pronounced non-Fermi-liquid features) towards a magnetically ordered, effectively twofold degenerate ground state in CeNi_8CuGe_4 with T_N = 175 +- 5 mK. Quantum critical behavior, C/T ~ \chi ~ -ln(T), is observed for x about 0.4. Hitherto, CeNi_{9-x}Cu_xGe_4 represents the first system where a substitution-driven quantum phase transition is connected not only with changes of the relative strength of Kondo effect and RKKY interaction, but also with a reduction of the effective crystal field ground state degeneracy.Comment: 15 pages, 9 figure
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