Spin-wave excitations in ferromagnetic thin films with nearest-neighbor and next-nearest-neighbor exchange interactions

Spin-wave excitations in a ferromagnetic thin film, where spins are coupled via exchange interactions with both nearest neighbors (J1) and next-nearest neighbors (J2), are studied by extending the theory developed by the present authors. It is shown that the amplitude of a spin wave is characterized by two kinds of wave vectors k1 and k2 perpendicular to the surfaces. The allowed values of these k1 and k2 are found to be real or complex depending on the spin-wave frequency ω and on the magnitude of J2J1. For space spin waves propagating through the film, the spin-wave resonance spectra and intensities are calculated in several cases for J2J1 values. For surface spin waves localized near the surfaces, the frequency is calculated as a function of the film thickness, and hence the thickness dependence on the stability condition for uniform ferromagnetic spin arrangement is studied.