Valence inhomogeneities in intermediate-valent Eu compounds

Abstract

In each of the intermediate valent compounds EuNi₂P₂, EuPd₂Si₂, and EuPd₆B₄, the line width of the ¹⁵¹Eu-Mössbauer resonance attains a maximum when its isomer shift varies most strongly with temperature. We associate this anomalous line broadening with a distribution of the local Eu valence, which may be described by an inhomogeneous width, Δ, of the interconfigurational excitation energy, E_exc, in addition to the homogeneous fluctuation width, k_BT_f. Applying this model to the analysis of isomer shift, line width, and magnetic susceptibility, the model parameters Δ, E_exc, and k_BT_f are obtained. Δ is found to attain maximal values at temperatures where E_exc varies most steeply with temperature.