A possible mechanism for quasi-two-dimensional ferromagnetism: The spectrum gap induced by s-d exchange interaction

A quasi-two-dimensional magnetic system is studied in which magnetic atoms are confined in the two-dimensional plane but the conduction electrons 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 mechanism is proposed for two-dimensional ferromagnetic order at finite temperature.