Spin-wave resonances in the presence of a Bloch wall

In-plane magnetized films of CoTaZr demonstrate standing spin-wave resonances in the complex permeability spectra well below the ferromagnetic resonance frequency. From detailed analysis of the static field dependence of the modes combined with observation of the domains using Kerr microscopy, we show that these modes originate from spin waves within the Bloch walls where the magnetization rotates perpendicular to the plane of the film. Unlike spin waves typically described in perpendicularly magnetized films, the frequencies involved are much lower due to unique field dynamics inside the wall. This theory can be fully understood by incorporating these observations into an analytical model using the Landau-Lifshitz-Gilbert equation, with good agreement between model and experimental measurement.