Electronic spectra and magnetic properties of RB6, RB12 and RB2C2 borides

Abstract

The electronic structures of RB 6 , RB 1 2 and RB 2 C 2 borides are studied ab initio by using the full-potential linear muffin-tin orbital method. This study includes the promising materials for spin electronics with reported high temperature ferromagnetism, namely, doped divalent hexaborides CaB 6 , SrB 6 , BaB 6 , and the CaB 2 C 2 compound, as well as Kondo semiconductors, SmB 6 and YbB 1 2 . For CaB 6 and SrB 6 a semiconducting band structure has been obtained, whereas a semimetallic ground state is revealed for CaB 2 C 2 and doped hexaborides. For YB 6 , LaB 6 , CaB 2 C 2 and the semimetallic Ba 1 - x La x B 6 alloys we have performed spin-polarized band structure calculations in an external field to evaluate the induced spin and orbital magnetic moments. These calculations indicate a feasibility of the field-induced weak ferromagnetic phase in CaB 2 C 2 and the La doped hexaborides. The LSDA and GGA calculations for different spin configurations of YbB 1 2 point to a possibility of antiferromagnetic coupling between Yb 3 + ions. For SmB 6 and YbB 1 2 our LSDA, GGA, and LSDA+U calculations have not revealed the hybridization gap for configurations with trivalent Sm 3 + and Yb 3 + .