The s-d (or s-f) interaction model is used to study the bulk and surface magnetic excitations of a semi-infinite ferromagnetic semiconductor. A formalism is established to obtain Green functions which provide the dynamic response of the system and from which the surface and bulk excitations and their dispersion relations are calculated. Results are deduced for both narrow-band and wide-band ferromagnetic semiconductors. The applicability to particular materials, such as the spinel-type ferromagnetic semiconductors is discussed.

• Received 18 July 1990

DOI:https://doi.org/10.1103/PhysRevB.42.10311