Anomalous crystal-field splittings of lanthanideS-states in metals

Compared are recent EPR, susceptibility, and neutron measurements of both S-state (b₄⁰) and non-S-state (A₄⁰〈r⁴〉) lanthanide-ion crystal-field splittings in metals. The ratio of the S-state to the non-S-state fields R=b₄⁰A₄⁰〈r⁴〉 in some metals is anomalously large and cannot be explained by the current insulator theory. We suggest that there must exist an extra "metallic" contribution to both A₄⁰〈r⁴〉 and the ratio R. The non-S-state field A₄⁰〈r⁴〉 is divided into two: (i) all Coulombic and exchange contributions, and (ii) a covalent contribution similar to that found in insulators. We show that the latter term is more efficient in its contribution to the S-state field b₄⁰. We suggest, in the anomalous metals, the S state b₄⁰ is dominated by covalent mixing but that for the non-S-state ions there is a partial cancellation between covalent and the coulomb-field contributions. Finally the implications for the Gd³⁺, 4f⁷ to 4f⁸ interconfigurational energy are explained.