Dynamic micromagnetic simulations of susceptibility spectra in thin films with nonuniform magnetization distributions

The high-frequency response of magnetic systems to a weak rf magnetic field can be characterized by the dynamic susceptibility tensor. The calculation of this quantity requires a precise knowledge of the magnetization configuration inside the sample. The aim of this paper is to demonstrate the ability of dynamic micromagnetic simulations for investigating the high-frequency susceptibility spectra of thin films with nonuniform magnetization distributions. As an illustrative example, the case of ferromagnetic films supporting a weak-stripe-domain structure is addressed. The zero-field susceptibility spectra over the frequency range 0.1-40 GHz are computed using a two-dimensional dynamic micromagnetic model. These spectra exhibit multiple resonances whose number and resonance frequencies depend on the equilibrium spin configuration and on the rf exciting field orientation. A modal analysis permits us to correlate these magnetic excitations with spin regions of the stripe domain structure. The influence of the uniaxial perpendicular anisotropy, the film thickness and an in-plane static magnetic field applied along the stripe direction on the main features of spectra (number of resonances, resonance frequencies, intensities, and linewidths) is then investigated. Finally, these theoretical results are discussed in light of available experimental data.