Dipole-exchange modes in multilayers with out-of-plane anisotropies

The collective modes of a multilayer constructed from alternating ultrathin films of ferromagnetic and nonmagnetic materials are calculated for cases in which the magnetic films have out-of-plane anisotropies. The collective surface and bulk modes of the system are predicted to strongly interact for certain values of the perpendicular anisotropy. A surprising result is the existence of a collective surface mode even when the nonmagnetic layer thicknesses are greater than the magnetic-layer thicknesses. Finally, the effects of small interlayer exchange interactions are examined and shown to result in a large broadening of the collective bulk spin-wave band.