A POSSIBLE MECHANISM FOR QUASI-2-DIMENSIONAL FERROMAGNETISM - THE SPECTRUM GAP INDUCED BY S-D EXCHANGE INTERACTION

A quasi-two-dimensional magnetic system is studied in which magnetic a toms are confined in the two-dimensional plane but the conduction elec trons are in fact three-dimensional. By virtue of spin-wave theory, we find that a spectrum gap can be formed at the bottom of the spin-wave spectrum, induced by the s-d exchange interaction between conduction electrons and magnetic localized electrons. Thus, a new possible mecha nism is proposed for two-dimensional ferromagnetic order at finite tem perature.