  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.
