Dinâmica generalizada para sistemas magnéticos nanoestruturados

Abstract

Microwave emission by magnetic materials at well-localized frequencies is of great interest for future nanotechnology applications. In this work a generalized model was developed to study the excitation spectra of nanostructured ferromagnetic systems using micromagnetic simulations with the implementation of the solving matrix method obtained through the Landau-Lifshitz equation and the dynamic susceptibility tensor method. The first part of the work was devoted to the analytical development of the equations of motion for a nanostructured ferromagnetic system, according to micromagnetic theory, and the expressions of the resolving matrix elements and the generalized dynamic susceptibility tensor elements. The theoretical models are then applied to describe the excitation spectra of systems such as uniformly magnetized ferromagnetic nanostripes, domain walls of ferromagnetic nanostripes coupled to antiferromagnetic vicinal substrates and magnetic vortices of circular nanodisks. The resolvent matrix allows obtaining the spectral density of states, and is applied to the study the spectra of domain walls, allowing the characterization of some modes of walls oscillations in a frequency range below the magnetic domain spectral band. Using the dynamic susceptibility tensor, the spatial distribution of resonance modes along the entire nanostructure could be identified. Thus, the similarities and differences between the domain, domain wall and vortex magnetic excitations can be investigated using the theoretical models developed in this study. Thus, we suggest, it possible to predict microwave field values to specifically excite each of the observed oscillation modes. The application of the model developed in systems such as nanodisks vortices and domain walls pinned by exchange interaction at the multilayer FM/AFM interface made it possible to identify considerable increases in resonance frequencies. For magnetic vortices, the smaller the nanodisk diameter, the higher the resonant frequency, while for domain walls, the narrower the wall (higher interface fields), the higher the resonant frequency.