Micromagnetic modeling of self-focusing effect of backward volume magnetostatic waves in iron-yttrium garnet films

Topic. Micromagnetic modeling of the propagation of backward volume magnetostatic waves (MSBVW) beams, excited by an antenna, placed in the center of yttrium iron garnet (YIG) film, has been carried out. Aim. To explore MSBVW-beam focusing with an increase in the amplitude of the exciting field at the antenna under conditions when only four-magnon (4M) processes are allowed for the MSBVW. Methods. The problem was solved using micromagnetic modeling by the finite-difference method solving the Landau-Lifshitz equation using the OOMMF software package. Results. It is shown that, depending on the position of the signal frequency in the MSBVW spectrum, an increase in the amplitude of the input signal above a certain threshold can lead to both the effect of wave beam focusing due to the development of modulation instability and the spatiotemporal chaotization of the amplitude distribution in the beam due to 4M decay processes. Changing of MSBVW-beam instability character at the frequency variation is associated with a change in the angular spectrum width of the beam and interaction between MSBVW and so-called "width" modes of the film. The obtained results can be used to analyze the effects of the propagation of nonlinear spin waves in YIG film waveguides.