Brillouin light-scattering observation of the nonlinear spin-wave decay in yttrium iron garnet thin films

Abstract

The direct observation of nonlinear spin-wave decay in thin yttrium iron garnet ͑YIG͒ films is reported. The second-order parametric spin waves were excited by a series of nonlinear magnetostatic backward volume wave ͑MSBVW͒ pulses propagated in a microstrip structure at 5 GHz. Brillouin light-scattering techniques were used to detect spin waves in the YIG at a point along the propagation path. Data were obtained as a function of the input pulse duty cycle and peak power level. These data yielded the decay rate eff for the parametric spin waves vs input power P in . This eff was equal to the usual spin-wave relaxation rate at low power, but decreased rapidly with increasing P in . As P in approached the threshold power for complete MSBVW soliton formation at the observation point, eff leveled off to a relatively constant value that was about a factor of 5-10 smaller than the low power value. The initial decrease in eff with power is due to the compensation of the usual spin-wave decay by the simultaneous parametric pumping of the spin waves by Suhl processes. The leveling off in eff at the soliton threshold is due to the spin-wave shedding that is needed to maintain order one eigenmode soliton propagation at high input power levels. These experiments demonstrate the reduction in the spin-wave decay rate with power below the threshold for spin-wave instability. This reduction is a key element in spin-wave instability theory that has never been observed directly. The data also demonstrate the enhanced production of parametric spin waves that accompanies microwave magnetic envelope soliton formation. §

Theoretical analysis of nonlinear pulse propagation in ferrite-dielectric-metal structures based on the nonlinear Schrödinger equation with higher order terms

“…The numerical analysis was done for an initial spatial pulse in the form of a super Gaussian u͑ y, 0͒ϭu 0 e Ϫ(y/2⌬) 4 , ͑4͒…”