DIAGRAMMATIC METHODS FOR STUDYING ELEMENTARY EXCITATIONS IN THIN MAGNETIC-FILMS

In this work we discuss a diagrammatic method for studying the long-wa velength magnetic excitation in an antiferromagnetic thin film. Althou gh we examine this particular system, the method is quite general. We pay special attention to the modes localized at the surface in the abs ence of an applied static external field. Such modes are more symmetri cal and more stable. There are two main results from this work. First, we transform the boundary condition into an abstract virtual potentia l which is used here to construct the Green's function for the element ary excitation in a film for a realistic situation. Second, we use suc h functions to obtain the surface dispersion relations and the power s pectra of the modes. Numerical applications are demonstrated, for MnF2 thin films.