Coexistence of localized and delocalized f-electrons inα−YbPdSnfrom thermodynamic and transport measurements

Abstract

We report the specific heat, magnetic susceptibility, and magnetization as well as resistivity of hexagonal $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Yb}\mathrm{Pd}\mathrm{Sn}$ polycrystals down to temperatures $T$ of $50\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$ and fields up to $12\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. In the susceptibility $\ensuremath{\chi}(T)$, several different temperature regimes can be distinguished. For $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}>T>170\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a Curie-Weiss-like behavior is obtained with the effective moments close to that of ${\mathrm{Yb}}^{3+}$. The large Weiss temperature ${\ensuremath{\Theta}}_{H}\ensuremath{\approx}150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and the leveling off of $\ensuremath{\chi}$ toward low $T$ are indicative of valence fluctuations. Around $30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, crystal-field excitations manifest themselves in features of $\ensuremath{\chi}(T)$ and the resistivity $\ensuremath{\rho}(T)$. For $5\phantom{\rule{0.3em}{0ex}}\mathrm{K}>T>0.2\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, a Curie-Weiss behavior with ${\ensuremath{\mu}}_{\mathit{eff}}=1.27{\ensuremath{\mu}}_{B}∕\mathrm{Yb}$ atom and ${\ensuremath{\Theta}}_{L}=0.41\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is found, signaling the occupation of the lowest crystal-field doublet. A sharp maximum in $\ensuremath{\chi}(T)$ and in the specific heat $C(T)$ indicates antiferromagnetic ordering at $250\phantom{\rule{0.3em}{0ex}}\mathrm{mK}$. The specific-heat peak develops into a broadened Schottky anomaly in moderate magnetic fields. The sizable linear specific-heat coefficient $\ensuremath{\gamma}=68\phantom{\rule{0.3em}{0ex}}\mathrm{mJ}∕\text{mole}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{2}$ is attributed to valence fluctuations. Likewise, the magnetization at 10 and $2.3\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ measured up to $12\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ 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 $\ensuremath{\sim}6%$ localized and $\ensuremath{\sim}94%$ delocalized moments derived from (nearly) trivalent Yb.