Dynamic Susceptibility in Thin Films with Antiferromagnetic Coupling between Layers

The dynamic susceptibility of the system with antiferromagnetic coupling between layers is investigated within the framework of the multiband model using the equation of motion with random phase approximation. Calculations are performed in the mixed Bloch-Wannier representation and a general form for χ is found. The susceptibility can be written in terms of two-particle Green's functions expressed in the local coordinate system with the z axis aligned along the local magnetization. The expression depends on an angle between the magnetization direction in a given layer and the crystal axis. Preliminary numerical calculations are performed for two systems: ultrathin Cr film and Fe/Cr multilayer structure. Imaginary part of the susceptibility corresponding to different layers is calculated and spin waves are discussed.