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arXiv · 1901.06826

Charge, lattice and magnetism across the valence crossover in EuIr$_2$Si$_2$ single crystals

Silvia Seiro·Yurii Prots·Kurt Kummer·Helge Rosner·Raúl Cardoso Gil·Christoph Geibel
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Abstract

We present a detailed study of the temperature evolution of the crystal structure, specific heat, magnetic susceptibility and resistivity of single crystals of the paradigmatic valence-fluctuating compound EuIr$_2$Si$_2$. A comparison to stable-valent isostructural compounds EuCo$_2$Si$_2$ (with Eu$^{3+}$), and EuRh$_2$Si$_2$, (with Eu$^{2+}$) reveals an anomalously large thermal expansion indicative of the lattice softening associated to valence fluctuations. A marked broad peak at temperatures around 65-75 K is observed in specific heat, susceptibility and the derivative of resistivity, as thermal energy becomes large enough to excite Eu into a divalent state, which localizes one f electron and increases scattering of conduction electrons. In addition, the intermediate valence at low temperatures manifests in a moderately renormalized electron mass, with enhanced values of the Sommerfeld coefficient in the specific heat and a Fermi-liquid-like dependence of resistivity at low temperatures. The high residual magnetic susceptibility is mainly ascribed to a Van Vleck contribution. Although the intermediate/fluctuating valence duality is to some extent represented in the interconfiguration fluctuation model commonly used to analyze data on valence-fluctuating systems, we show that this model cannot describe the different physical properties of EuIr$_2$Si$_2$ with a single set of parameters.

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Silvia Seiro, Yurii Prots, Kurt Kummer, Helge Rosner, Raúl Cardoso Gil, Christoph Geibel. 2019-01-21. Charge, lattice and magnetism across the valence crossover in EuIr$_2$Si$_2$ single crystals. https://doi.org/10.1088/1361-648x%2Fab1509

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