Effect of Strong Correlation on a Mixed Valence System

Abstract

In recent years a great deal of research has been done on some rare-erath metals and their compounds which show the mixed valence or valence fluctuating phenomena [1], Properties of this kind of materials are full of variety from material to material. Among them, in this paper we consider the case where one configuration is magnetic, e.g. ${\text{Sm}}^3+\left(^6 {\text{H}}_{5 \mathord{\left/ {\vphantom {5 2}} \right. 2}}\right)$ and ${\text{Ce}}^3+\left(^2 {\text{F}}_{5 \mathord{\left/ {\vphantom {5 2}} \right. 2}}\right)$ , and the other is nonmagnetic, e.g. ${\text{Sm}}^2+\left(^7 {\text{F}}_0\right)$ and ${\text{Ce}}^4+\left(^1{\text{S}}_0\right)$ . Magnetic property of this class of materials has a characteristic feature. At high temperatures susceptibility is expressed by the formula

$$ {\text{X = C}}_{\text{I}} {\text{X}}_{\text{I}} {\text{ + C}}_{\text{II}} {\text{X}}_{\text{II}}, $$

(1)

where X_I(X_II) is the susceptibility expected for one valence state and C_I(C_II) is its fraction. In a word, high-temperature property is characterized by a local-moment-type behavior. On the other hand, at low temperatures the susceptibility tends to a constant and no magnetic order is observed.