Papers by Keyword: Heavy Fermion

Abstract: The recent discovery of topological Kondo insulating behaviour in strongly correlated electron systems has generated considerable interest in Kondo insulators both experimentally and theoretically. The Kondo semiconductors CeT₂Al₁₀ (T=Fe, Ru and Os) possessing a c-f hybridization gap have received considerable attention recently because of the unexpected high magnetic ordering temperature of CeRu₂Al₁₀ (T_N=27 K) and CeOs₂Al₁₀ (T_N=28.5 K) and the Kondo insulating behaviour observed in the valence fluctuating compound CeFe₂Al₁₀ with a paramagnetic ground state down to 50 mK. We are investigating this family of compounds, both in polycrystalline and single crystal form, using inelastic neutron scattering to understand the role of anisotropic c-f hybridization on the spin gap formation as well as on their magnetic properties. We have observed a clear sign of a spin gap in all three compounds from our polycrystalline study as well as the existence of a spin gap above the magnetic ordering temperature in T=Ru and Os. Our inelastic neutron scattering studies on single crystals of CeRu₂Al₁₀ and CeOs₂Al₁₀ revealed dispersive gapped spin wave excitations below T_N. Analysis of the spin wave spectrum reveals the presence of strong anisotropic exchange, along the c-axis (or z-axis) stronger than in the ab-plane. These anisotropic exchange interactions force the magnetic moment to align along the c-axis, competing with the single ion crystal field anisotropy, which prefers moments along the a-axis. In the paramagnetic state (below 50 K) of the Kondo insulator CeFe₂Al₁₀, we have also observed dispersive gapped magnetic excitations which transform into quasi-elastic scattering on heating to 100 K. We will discuss the origin of the anisotropic hybridization gap in CeFe₂Al₁₀ based on theoretical models of heavy-fermion semiconductors.

Abstract: PrFe₄P₁₂ shows an anomalously phase transition from a heavy fermion (HF) state to a non-magnetic ordered state. We prepared single crystal sample of Pr (Fe_1-xCo_x)₄P₁₂ by Sn-flux method to investigate the effects of electron doping. The distinct change of magnetic property was observed. The phase transition of PrFe₄P₁₂ rapidly disappears when doped rate x=0.03. This result indicates that the d-electron plays an important role in formation of Low-temperutre phase and HF state of PrFe₄P_12.

Abstract: The new compound UCo3-xGex with x = 0.4 was prepared by direct solidification of the corresponding liquid phase, followed by annealing at 973 K. Single crystal X-ray diffraction carried out at room temperature showed that it crystallizes with the hexagonal space group P63/mmc (n°194) and the unit-cell parameters a = 4.890(5) Å and c = 16.405(5) Å. The substitution of Co atoms by germanium atoms in UCo3 (PuNi3 structure type) yields stabilization of the CeNi3 structure. The homogeneity range, evaluated by energy dispersive spectroscopy analysis, extends from x = 0.2(1) to 0.4(1). The electronic properties were investigated by means of DC magnetic susceptibility and DC electrical resistivity measurements. The phase is a Pauli paramagnet and exhibits electrical conductivity characteristic of strongly disordered metals.

Abstract: CeRhSb is known as a Kondo insulator with a hybridization gap Eg/kB  7 K. By doping CeRhSn with Pd this gap is strongly reduced and completely removes for x>0.08 in the system of CeRh1-xPdxSb alloys. The specific heat C of the samples 0x0.08 shows the heavy-Fermi-like behavior in the form of an strongly enhanced Sommerfeld coefficient CTT, which follows below 8 K a power law over a decade in temperature. Our measurements suggest that the enhanced  value originates from correlated, residual in-gap states at the Fermi level.