Nonlinear spin-wave propagation in the nonidentical magnonic structures

Topic. Investigation of nonlinear propagation modes of a spin-wave signal in lateral non-identical structures, taking into account the multi-mode spin waves. Aim. Consideration of the effect of intermode coupling on the intensity distribution of surface magnetostatic waves propagating in lateral waveguides of various widths. Identify the possibility of changing the coupling coefficient by varying the power of the input signal. Methods. The study of nonlinear propagation modes of spin waves was carried out by numerical integration of a system of two coupled Ginzburg–Landau equations. The calculation of the values of the coupling coefficient of the spin waves between the lateral waveguides and the proportionality coefficient was carried out using the finite element method. Using micromagnetic simulation, the Landau–Lifshitz–Gilbert equation was solved using the finite difference method to obtain maps of the distribution of the dynamic magnetization of spin waves. Results. It is shown that the mode of operation of a nonlinear directional coupler based on the lateral system of nonidentical microwave channels is determined by the geometrical parameters of the structure, namely, the ratio of the widths of the microwave channels. Inhomogeneous distribution of the internal magnetic field and a change in the width of one of the microwave lead to a change in the threshold power of the microwave signal, at which the effects of the variation of the coupling length of spin waves and a nonlinear switching signal are observed. Discussion. The dependence of the coupling length of the spin waves on the input signal power allows the directional coupler of the information signal to operate in a nonlinear mode. Due to the possibility of tuning the frequency band by changing the magnitude of the magnetic field, it is possible to fabricate magnonic based microwave signal processing devices, such as nonlinear demultiplexers, power splitters and directional microwave signal couplers.