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

The electronic structures of R B6, R B12 and R B2C2 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 CaB6, SrB6, BaB6, and the CaB2C2 compound, as well as Kondo semiconductors, SmB6 and YbB12. For CaB6 and SrB6 a semiconducting band structure has been obtained, whereas a semimetallic ground state is revealed for CaB2C2 and doped hexaborides. For YB6, LaB6, CaB2C2 and the semimetallic Ba1–x Lax B6 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 CaB2C2 and the La doped hexaborides. The LSDA and GGA calculations for different spin configurations of YbB12 point to a possibility of antiferromagnetic coupling between Yb3+ ions. For SmB6 and YbB12 our LSDA, GGA, and LSDA+U calculations have not revealed the hybridization gap for configurations with trivalent Sm3+ and Yb3+. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)