Ferromagnetism below the Stoner limit in La-doped SrB_6

Abstract

Spin-polarized band calculations for LaSr_7B_{48} show a weak ferro-magnetic state. This is despite a low density-of-states (DOS) and a low Stoner factor. The reason for the magnetic state is found to be associated with a gain in potential energy in addition to the exchange energy, as a spin-splitting is imposed. An impurity like La DOS is essential for this effect. It makes a correction to the Stoner factor, and provides an explanation of the recently observed weak ferro-magnetism in doped hexaborides.Comment: 6 pages, 2 tables, 1 figur