Synthesis, crystal structure, and physical properties of YbTZn (T= Pd, Pt and Au) and LuPtZn

We report the synthesis of three new Yb-based equiatomic compounds YbPdZn, YbPtZn, and YbAuZn, and of LuPtZn. According to the results of x-ray diffraction, these four compounds crystallize in the TiNiSi-type structure (orthorhombic oP12-Pnma, an ordered ternary variant of the Co2Si type). The Yb ions in YbPdZn and YbAuZn are in the divalent state, while a strong interplay of the single-ion Kondo and magnetic exchange interactions is observed in YbPtZn. The electrical resistivity of YbPtZn increases with decreasing temperature below 300 K, peaks broadly around 45 K, and decreases precipitously below 10 K. A rapidly increasing C4f∕T, where C4f is the 4f-derived contribution to the heat capacity at low temperatures, indicates the onset of a heavy fermion state which orders magnetically at 1.35 K; a reduced magnetic entropy of just 1.6 J∕mol K up to the ordering temperature indicates a small moment state in which the Yb-magnetic moment is appreciably screened by the Kondo interaction. The coefficient of the linear term in the electronic specific heat γ obtained from extrapolating the zero-field data below 0.4 K to T=0 K in the magnetically ordered state is 0.75 J∕mol K2, showing a strongly renormalized electronic state due to the Kondo interaction. γ decreases rapidly in applied magnetic fields due to the weakening of the Kondo interaction. The heat capacity and magnetoresistivity data indicate the presence of ferromagnetic correlations between the Yb ions. Such a feature is rare in Yb-based Kondo compounds.