Spin-polarized band calculations for LaSr7B48 show a weak ferromagnetic sta
te. 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 i
s imposed. A DOS with an impuritylike La band is essential for this effect.
It makes a correction to the Stoner factor and provides an explanation of
the recently observed weak ferromagnetism in doped hexaborides.