Coexistence of localized and delocalized f-electrons in α-YbPdSn from thermodynamic and transport measurements

We report the specific heat, magnetic susceptibility, and magnetization as well as resistivity of hexagonal α-YbPdSn polycrystals down to temperatures T of 50 mK and fields up to 12 T. In the susceptibility χ(T), several different temperature regimes can be distinguished. For 300 K>T>170 K, a Curie-Weiss-like behavior is obtained with the effective moments close to that of Yb>sup>3+. The large Weiss temperature ΘH≈150 K and the leveling off of χ toward low T are indicative of valence fluctuations. Around 30 K, crystal-field excitations manifest themselves in features of χ(T) and the resistivity ρ(T). For 5 K>T>0.2 K, a Curie-Weiss behavior with µ_eff=1.27µ_B/Yb atom and Θ_L=0.41 K is found, signaling the occupation of the lowest crystal-field doublet. A sharp maximum in χ(T) and in the specific heat C(T) indicates antiferromagnetic ordering at 250 mK. The specific-heat peak develops into a broadened Schottky anomaly in moderate magnetic fields. The sizable linear specific-heat coefficient γ=68 mJ/mole K² is attributed to valence fluctuations. Likewise, the magnetization at 10 and 2.3 K measured up to 12 T can be decomposed into a contribution of delocalized electrons and localized magnetic moments. The data can be consistently interpreted in terms of a two-fluid model with ~6% localized and ~94% delocalized moments derived from (nearly) trivalent Yb.