THE DISPERSION-RELATION IN ANTIPARALLEL COUPLED FERROMAGNETIC-FILMS

The dispersion relation of the system with two identical magnetic layers antiparallel coupled is modified from the normal antiferromagnetic material as well as that of the single ferromagnetic layer. With the external field in the film plane parallel to the in-plane easy axis, three unique regions exist as the antiparallel, canted and saturation region. The resonance field of the acoustic mode shifts significantly compared with that of a noncoupled layer system if the magnetization is not saturated. No antiparallel state exists with the external field perpendicular to the film plane and a minimum frequency, omega = 2gammaH(E), is required to observe the acoustic resonance mode. In each orientation the optical mode exists at a field of 2H(E) higher than that of the acoustic mode in the saturation region. These calculations are very helpful to understand the unusual ferromagnetic resonance spectrum in the strong antiparallel coupled bilayer system being investigated in this lab.