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.
Crystal structure, magnetic ordering, and magnetic excitation in the 4f-localized ferromagnet CeAgSb2
Systematic neutron-scattering experiments have been carried out in order to reveal the crystal and magnetic structures as well as the magnetic excitation in the Ce-based intermetallic compound ${\mathrm{CeAgSb}}_{2}.$ It was clarified that the Ag atoms in ${\mathrm{CeAgSb}}_{2}$ (space group: $\mathrm{P}4/nmm)$ occupy the 2b site, while Sb atoms occupy $2a$ and $2c$ sites, which have, to date, been controversial in literature. From the analysis of neutron powder-diffraction profile, we found the existence of the ferromagnetic component of about $0.41{\ensuremath{\mu}}_{\mathrm{B}}/\mathrm{Ce}$ oriented along the c axis, consistent with the result of previous studies. On the other hand, however, no trace of the antiferromagnetic or spin-density wave peak was detected within our range of experimental accuracy. We observed a considerable spin-wave excitation below 3 meV. The dispersion relation was explained by the anisotropic Heisenberg model. This means that ${\mathrm{CeAgSb}}_{2}$ has a simple ferromagnetic structure. Furthermore, crystalline electric-field (CEF) excitations were observed at 5.2 and 12.5 meV in the paramagnetic state, which is indicative of the localized nature of the $\mathrm{Ce}\ensuremath{-}4f$ electron. Our analysis revealed that $|{J}_{z}=\ifmmode\pm\else\textpm\fi{}\frac{1}{2}〉$ is the ground state, while the first and second excited levels are mainly due to $|\ifmmode\pm\else\textpm\fi{}\frac{3}{2}〉$ and $|\ifmmode\pm\else\textpm\fi{}\frac{5}{2}〉,$ respectively. The observed ferromagnetic moment is in good agreement with the ground-state saturation moment, ${g}_{J}{\ensuremath{\mu}}_{\mathrm{B}}{J}_{\mathrm{z}}\ensuremath{\sim}0.43{\ensuremath{\mu}}_{\mathrm{B}}.$ The susceptibility, magnetization curve, and magnetostriction can be explained in terms of the CEF level scheme with anisotropic exchange interaction.