Interpocket polarization model for ordering structures in rare-earth hexaborides

Abstract

Origin of the common ordering structure in cubic rare-earth (R) hexaborides RB 6 is ascribed to an RKKY polarization connecting different pockets of the conduction band. In order to account for the band structure common to RB 6, a tight-binding model is used which reproduces the Fermi surface reasonably well. The model includes 2p t 2u molecular orbitals for each B 6 cluster and 5d e g orbitals for each rare-earth ion. The resultant intersite interaction I( q) gives rise to a broad maximum around q=( 1 4 , 1 4 , 1 2 ) in the Brillouin zone, provided both 2p and 5d components of the conduction band participate in the exchange interaction. This wave number corresponds to the ordering pattern in GdB 6 and some other rare-earth hexaborides.