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Register a new userPhysical properties of the very heavy fermion YbCu4Ni
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The physical properties of the very heavy fermion YbCu$_4$Ni were characterized through structural, magnetic, thermal and transport studies along nearly four decades of temperature ranging between 50 milikelvin and 300 K. At high temperature, the crystal electric field levels splitting was determined with $Delta_1 (Gamma_6)= 85$ K and $Delta_2 (Gamma_8) approx 200$ K, the latter being a quartet in this cubic symmetry. An effective magnetic moment $mu_{eff} approx 3mu_B$ is evaluated for the $Gamma_7$ ground state, while at high temperature the value for a Yb$^{3+}$ ion is observed. At low temperature this compounds shows the typical behavior of a magnetically frustrated system undergoing a change of regime at a characteristic temperature $T^*approx 200$ mK into a sort of Fermi-liquid type plateauof the specific heat: $C_m/T|_{Tto 0}$ = const. The change in the temperature dependence of the specific heat coincides with a maximum and a discontinuity in respective inductive and dissipative components of the ac-susceptibility. More details from the nature of this ground state are revealed by the specific heat behavior under applied magnetic field.
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We report the synthesis, crystal structure and characterization by means of single crystal x-ray diffraction, neutron powder diffraction, magnetic, thermal and transport measurements of the new heavy fermion compounds Ce$_{2}$MAl$_{7}$Ge$_{4}$ (M = Co, Ir, Ni, Pd). These compounds crystallize in a noncentrosymmetic tetragonal space group P={4}2$_{1}$m, consisting of layers of square nets of Ce atoms separated by Ge-Al and M-Al-Ge blocks. Ce$_{2}$CoAl$_{7}$Ge$_{4}$, Ce$_{2}$IrAl$_{7}$Ge$_{4}$ and Ce$_{2}$NiAl$_{7}$Ge$_{4}$ order magnetically behavior below $T_{M}=$ 1.8, 1.6, and 0.8 K, respectively. There is no evidence of magnetic ordering in Ce$_{2}$PdAl$_{7}$Ge$_{4}$ down to 0.4 K. The small amount of entropy released in the magnetic state of Ce$_{2}$MAl$_{7}$Ge$_{4}$ (M = Co, Ir, Ni) and the reduced specific heat jump at $T_M$ suggest a strong Kondo interaction in these materials. Ce$_{2}$PdAl$_{7}$Ge$_{4}$ shows non-Fermi liquid behavior, possibly due to the presence of a nearby quantum critical point.
A technique for measuring the electrical resistivity and absolute thermopower is presented for pressures up to 30 GPa, temperatures down to 25 mK and magnetic fields up to 10 T. With the examples of CeCu2Ge2 and CeCu2Si2 we focus on the interplay of normal phase and superconducting properties. With increasing pres- sure, the behaviour of CeCu2Ge2 evolves from that of an antiferromagnetically ordered Kondo system to that characteristic of an intermediate valence compound as the Kondo temperature increases by about two orders of magnitude. In the pressure window 8-10 < P < 20 GPa, a superconducting phase occurs which com- petes at low pressure with magnetic ordering. For CeCu2Si2 the effective mass of carriers is probed by both the coefficient of the Fermi liquid law and the ini- tial slope of the upper critical field. The magnetic instability is studied no- tably for CeRu2Ge2 and Yb-based compounds for which pressure-induced magnetic ordering tends to develop. Finally, contrary to conventional wisdom, we argue that in heavy fermions a large part of the residual resistivity is most likely not independent of temperature; tentatively ascribed to Kondo hole, it can be very pressure as well as sample dependent. [electrical resistivity, thermoelectric power, heavy fermion, magnetic order, superconductivity]
Some recent neutron scattering works on CeRhIn5 and Ce2RhIn8, together with related resistivity and specific heat measurements, are summarized. In spite of its layered crystal structure, CeRhIn5 is shown to be 3-dimensional both magnetically and in transport. We also find that the Fisher-Langer behavior is closely followed in CeRhIn5. This may circumvent the Kondo lattice model and support applying established Fermi-liquid superconductivity theory to heavy fermion superconductors.
We have measured the electrical resistivity, thermoelectric power, Hall coefficient, and magnetoresistance (MR) on single crystals of PrOs$_{4}$Sb$_{12}$, LaOs$_{4}$Sb$_{12}$ and NdOs$_{4}$Sb$_{12}$. All the transport properties in PrOs$_{4}$Sb$_{12}$ are similar to those in LaOs$_{4}$Sb$_{12}$ and NdOs$_{4}$Sb$_{12}$ at high temperatures, indicating the localized character of 4$f$-electrons. The transverse MR both in LaOs$_{4}$Sb$_{12}$ and PrOs$_{4}$Sb$_{12}$ tends to saturate for wide field directions, indicating these compounds to be uncompensated metals with no open orbit. We have determined the phase diagram of the field induced ordered phase by the MR measurement for all the principle field directions, which indicates an unambiguous evidence for the $Gamma_{rm 1}$ singlet crystalline electric field ground state.
We report the crystal structure and highly-anisotropic magnetic, transport and thermal properties of an exceptionally good single crystal of U(Ru0.92Rh0.08)2Si2 prepared using a modified Czochralski method. Our study, that also includes neutron diffraction results, shows all the heavy-fermion signatures of pristine URu2Si2 , however, the superconductivity, hidden order and remanent weak antiferromagnetic orders are absent. Instead, the ground state of the doped system can be classified as a spin liquid that preserves the heavy-fermion character. U(Ru0.92Rh0.08)2Si2 exhibits a short-range magnetic order distinguished by reflections of a Lorentzian profile at qIII = (1/2 1/2 1/2) positions that disappear above approx. 15 K. The short-range order seems to be a precursor of a long-range magnetic order that occurs with higher Rh concentration. We indicate that these short-range fluctuations involve, at least partially, inelastic scattering processes.
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