Influence of input signal power on magnetostatic surface waves propagation in yttrium-iron garnet films on silicon substrates

Yttrium iron garnet (YIG) films on silicon substrates (Si) are of a great interest due to compatibility of their fabrication with semiconductor technologies and, thus, possible integration of magnonic and electronic devices on one chip. However, features of spin wave propagation in YIG films on semiconductor substrates remain almost unexplored.
In this work with the help of network analyzer and microwave probe station we investigate the influence of input signal power on propagation of magnetostatic surface waves (MSSW) in the delay line structures based on YIG/Si films deposited by ion-beam evaporation.
It is shown that dependence of output MSSW power ($P_{\rm out}$) on input power level ($P_{\rm in}$) is determined by the position of MSSW frequency relative to the frequency $f_{\rm max}$ corresponding to the maximum of MSSW transmission spectrum. For frequencies $f>f_{\rm max}$ the dependence $P_{\rm out}(P_{\rm in})$ monotonically decreases with input power growth while at frequencies $f<f_{\rm max}$ it has the maximum. Such behavior is qualitatively different from the dependences $P_{\rm out}(P_{\rm in})$ of epitaxial YIG films on substrates from gadolinium-gallium garnet (GGG).
We assume that described features result from the higher damping level (two orders greater) of spin waves in YIG/Si films comparing to the epitaxial YIG/GGG structures. As a consequence, thresholds of MSSW parametric instability considerably increase, MSSW spectrum shifts towards the lower frequencies because of dynamic demagnetization and thermal heating induced by microwave power of propagating wave. In turn, this shift strongly influences the behavior of $P_{\rm out}(P_{\rm in})$ dependence. Thus, the described effect should be considered for the identification of true thresholds of parametric instability of spin waves in YIG/Si films.