Influence of the nickel concentration on the magnetic properties of the cerium filled nickel substituted skutterudites

According to numerous authors, filled skutterudites which are promising thermoelectric compounds are characterized by very anomalous magnetic propel ties. Although containing cerium, iron and nickel or cobalt, these compounds. whatever the composition, do not order at low temperature. The magnetic susceptibility of nickel-poor compounds show a large deviation from the classical Curie-Weiss law. The effective magnetic moment of the semiconducting samples indicates that neither nickel nor iron are magnetic. These properties could indicate a temperature depending valency of the cerium ion, a crystal field effect or a heavy fermion behavior. In order to check some of these hypotheses we have performed magnetic and X-ray absorption experiments on nickel substituted cerium filled skutterudites. Our results presented in this paper confirm the valency 3 + of the cerium ion and corroborate the heavy fermion hypothesis. (C) 2000 Elsevier Science S.A. All rights reserved.