Abstract: We have investigated the physical properties of CeRuSi, its homologue CeRuGe and some doped La alloys. All of them present similar properties: large paramagnetic temperatures θp ##IMG## [http://ej.iop.org/icons/Entities/approx.gif] {approx} −100 K and the level off of χ( T ) below ##IMG## [http://ej.iop.org/icons/Entities/approx.gif] {approx} 10 K in coincidence with the maximum decrease of p ( T ), which starts to drop below 25 K. The respective γ ( CeRuSi ) ##IMG## [http://ej.iop.org/icons/Entities/approxeq.gif] {approxeq} 0.18 and γ ( CeRuGe ) ##IMG## [http://ej.iop.org/icons/Entities/approxeq.gif] {approxeq} 0.15 J/molK 2 coefficients reveal a heavy fermion character, with a Kondo temperature T K ##IMG## [http://ej.iop.org/icons/Entities/approxeq.gif] {approxeq} 50 K comparable to the crystal field splitting. In both compounds a broad maximum in C P ( T )/ T is observed around 5 K, whose origin is yet not clear. In contrast to the usual behavior observed in Kondo lattice systems, when Si is replaced by Ge T K ##IMG## [http://ej.iop.org/icons/Entities/propto.gif] {propto} θ p and 1/γ practically does not decreases despite the unit cell volume of CeRuGe is about 3% larger than that of CeRuSi. We discuss possible origins for these unusual features.

Abstract: The physical properties of the very-heavy-fermion compound YbCu4Ni were characterized through structural, magnetic, thermal, and transport studies along nearly four decades of temperature ranging between 50 mK and 300 K. At high temperature, the crystal electric field level splitting was determined with Δ1(Γ6)=85K and Δ2(Γ8)≈200K, the latter being a quartet in this cubic symmetry. An effective magnetic moment μeff≈3μB is evaluated for the Γ7 ground state, while at high temperature the value for a Yb3+ ion is observed. At low temperature this compound shows the typical behavior of a magnetically frustrated system undergoing a change of regime at a characteristic temperature T∗≈200mK into of Fermi-liquid-type “plateau” of the specific heat: Cm/T|T→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 about the nature of this ground state are revealed by the specific heat behavior under applied magnetic field.

Abstract: The magnetic, thermal, and transport properties of the noncentrosymmetric compound Eu2Pd2Sn are reexamined with the inclusion of detailed measurements. In its paramagnetic phase, the outstanding feature of this compound is the formation of Eu2+ dimers, which allows us to understand the deviation of the magnetic susceptibility χ(T) from the Curie-Weiss law below about 70 K, the field-dependent magnetization M(B) below ≈80 K , and the reduced entropy at the ordering temperature S(TN)=0.64Rln(8). A significant change in the exchange interactions occurs between T≈70K (where θP=18K) and TN=13.3K (to θP=−4.5K). The strong electronic overlap, arising from the reduced Eu-Eu spacing (compared with that in pure Eu2+) is expected to favor dimer quasiparticles formation, leading to a significant change in the magnetic structure. From the analysis of the derivatives of the magnetic parameters, ∂χ/∂T and ∂M/∂B, as well as the field dependence of the specific heat and mangnetoresistance, a comprehensive magnetic phase diagram is obtained. Two critical points are recognized and a tentative description of the magnetic structures is proposed. The possible formation of a skyrmion lattice, arising from the presence of magnetically frustrated pockets in the phase diagram, is suggested by theoretical studies on hexagonal structures that exhibit similar interaction patterns.