Evolution of magnetism from mixed-valent CeIr₃B₂ to trivalent CeIr₃Si₂

Abstract

The ternary compound CeIr₃B₂ is a mixed-valent material crystallizing in a monoclinic structure, closely related to the hexagonal CeCo₃B₂-type structure. The structural and magnetic phase diagrams of the systems CeRh_3-yIr_yB₂ (y=0-2) and CeIr₃B_2-xSi_x (x=0-2) have been investigated. Properties of the new compound CeIr₃Si₂ have been reported for the first time. It is shown that the structure of CeIr₃B₂ transforms to the hexagonal type on substitution of Rh and Si at Ir and B sites, respectively. Accompanying the structural transformation is an electronic transition in which the mixed-valent Ce atoms become more magnetic. The observed ferromagnetic ground state is similar to the one seen in CeRh₃B₂ (T_c=115 K and μ_sat=0.4μ_B). The role of Ce-atom ligands and their hybridization is thought to be the primary cause for the unusual nature of magnetism in CeT₃B₂-type compounds.