Influence of parametric instability of magnetostatic surface spin waves on formation of defect modes in one-dimensional magnonic crystal with defect

Propagation of nonlinear magnetostatic surface waves through the one-dimensional magnonic crystal based on yttrium-iron garnet film with the defect of periodic array was experimentally studied. Interest in the study of the magnonic crystals with defects is caused by the possibility of exciting of defect modes inside the forbidden gaps of MSSW spectrum that can be used to enhance the non-linear effects and signals control in the microwave range. The studied structure was developed by etching of the periodic array of grooves with the defect in the form of increasing of the one separation width between two grooves up to the period of the surface structure. Magnetostatic surface waves were excited in the structure. Frequency dependencies of transmission and reflection coefficients were studied for different levels of the pump signal using a microwave network analyzer. It was found that defect mode fade out as a result of three-magnon process. The threshold power for this process is less than the same parameter for Bragg resonance as a result of effect of local increasing of spin wave field as well as because of formation of non-equilibrium region of spin wave propagation that is localized near the defect. The shift of defect mode frequency and Bragg forbidden gap toward long wavelength limit of MSSW spectrum was found in the condition of four-magnon process at high pumping level as a result of change of MSSW dispersion at large angles of magnetization precession.