Magnetic and transport properties of PrRhSi3
We have investigated the magnetic and transport properties of a noncentrosymmetric compound PrRhSi3 by dc magnetic susceptibility χ(T), isothermal magnetization M(H), thermoremanent magnetization M(t), specific heat Cp(T), electrical resistivity ρ(T,H) and muon spin relaxation (μSR) measurements. At low fields χ(T) shows two anomalies near 15 and 7 K with an irreversibility between ZFC and FC data below 15 K. In contrast, no anomaly is observed in Cp(T) or ρ(T) data. M(H) data at 2 K exhibit very sharp increase below 0.5 T and a weak hysteresis. M(t) exhibits very slow relaxation, typical for a spin-glass system. Even though the absence of any anomaly in Cp(T) is consistent with the spin-glass type behavior, there is no obvious origin of spin-glass behavior in this structurally well ordered compound. The crystal electric field (CEF) analysis of Cp(T) data indicates a CEF-split singlet ground state lying below a doublet at 81(1) K and a quasi-triplet at 152(2) K. The ρ(T) data indicate a metallic behavior, and ρ(H) exhibits a very high positive magnetoresistance, as high as ∼300% in 9 T at 2 K. No long range magnetic order or spin-glass behavior was detected in a μSR experiment down to 1.2 K.
A new ternary magnetically ordered heavy fermion compound Pr2Rh3Ge: magnetic, electronic and thermodynamic properties
The results of the magnetic, electron transport, heat capacity and heat conduction measurements on the new rhombohedral ternary compound Pr2Rh3Ge have been investigated. The synthesized polycrystalline compound was found to crystallize in the ternary ordered variant of the cubic Laves phase MgCu2-type of structure with the space group R3¯m, as previously reported. Pr2Rh3Ge exhibits a ferromagnetic behaviour below TC=8.5 K, which was found to be unstable in low applied magnetic fields, revealing characteristics usually attributed to the long-range order. In the entire paramagnetic region electrical resistivity shows monotonous metallic conductivity character. We estimated that the Sommerfeld coefficient γ  =  315 mJ/Pr-mol · K2 of Pr2Rh3Ge is very large with comparison to ordinary metals which indicate the existence of heavy fermion behaviour of itinerant charge carriers at low temperatures or enhanced density of the quasi-particle state at the Fermi level. The crucial role of the crystalline electric field effects on the ground state properties of Pr3+ (J  =  4) has been also observed. We think that the heavy fermion behaviour in Pr2Rh3Ge results from the dynamic low-lying crystal-field fluctuations, since there is no sign of Kondo effect in electrical resistivity and no enhancement of the slope S(T)/T in thermoelectric power data at low temperatures. It suggests that the conduction electrons at the Fermi level does not correlate with the 4f2 states of Pr3+ atoms and hence there is no place for a typical spin Kondo effect, as it is commonly observed in Ce- and Yb-based heavy fermion systems.
Low-Temperature Magnetic Properties of Several Compounds in Ce-Pd-X (X=Si, Ge and Al) Ternary Systems
We have investigated several ternary compounds of cerium in the Ce-Pd-X (X=Si, Ge and Al) systems and their La counterparts by measuring the magnetic susceptibility, electrical resistivity and specific heat. The Ce ions in these compounds are in the nearly trivalent state and most of them show magnetic order of either long-range or spin-glass type at low temperatures. None of them distinctly exhibits the heavy fermion behavior, although it may be obscured by atomic disorder in some compounds. The relation between several isostructural ternary compounds of Ce-Pd-(Si and Ge) or Ce-Pd-(Al and Ga) system is qualitatively discussed in the framework of the Doniach phase diagram. The variation of the unit cell volume suggests that the former group is consistent with this phase diagram but the latter is not seemingly so. We found that LaPdSi 3 and LaPd 0.6 Ge 1.4 among the La counterparts are superconducting below 2.6 and 2.8 K, respectively.