Heuristic model for magnetic-nonmagnetic transitions in intermediate-valence systems

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Abstract
We present a simple conceptual discussion of the competition between hybridization and exchange in the problem of magnetic-nonmagnetic transitions in intermediate-valence systems. Two atomic-like calculations are presented: a singlet-doublet and a doublet-doublet level systems. A phenomenological ferromagnetic coupling is introduced. In the singlet-doublet case, three distinct phases are possible: paramagnetic, induced ferromagnetic, and ferromagnetic, depending on the values of the parameters. Results for the enhanced susceptibility are also presented. In the doublet-doublet case, two phases occur, para- and ferromagnetic. The valence change upon ordering is discussed. We argue that not only the "magnetic" character of the configuration, but also the relative strength of the local-moment quenching component of the hybridization potential and of the exchange interaction, are important in determining the existence of a spontaneously polarized phase.