Micromagnetic Modeling of Parametric Amplification of Forward Volume Spin Waves by Noncollinear Surface Acoustic Waves

Micromagnetic modeling is used to simulate the parametric amplification of forward volume spin waves by a surface acoustic wave (SAW) traveling noncollinearly in a yttrium–iron–garnet thin film. The angle of incidence between the signal spin wave and the SAW pump determines the strength of parametric coupling as well as the propagation direction of the resulting idler spin wave. In a collinear arrangement, where the spin wave and SAW travel together, the acoustic pump amplitude needed to achieve amplification is greater than the threshold for the parametric generation of spin waves from the thermal background. However, in a noncollinear arrangement with >35° angle of incidence between the signal spin wave and SAW pump, the coupling is enhanced and allows for continuous amplification of spin waves by more than 10× without simultaneously resulting in unconstrained growth of thermal spin waves. The angular dependence of the parametric coupling strength, as determined from the simulations, agrees qualitatively with theoretical predictions.