Nonlinear magnon study by microwave perpendicular pumping ferromagnetic resonance in thin films*

To investigate the nonlinear effects arising from magnon coupling to microwaves and their application to the new functionality of monolithically integrated magnetic components on semiconductor substrates, it is important to exploit non-linear ferromagnetic resonance in magnetic insulator materials. We have studied the nonlinearity caused by the three magnon scattering mechanism in GHz ferromagnetic resonance in simulation and analytically. The thicknesses of the studied YIG films are varied in the range of nanometers to several micrometers. A realistic micromagnetic simulation is implemented to capture the physical mechanisms coupling magnons of sub-micrometer wavelengths and microwaves of centimeter wavelength using CUDA parallel high-performance computing. Using the Holstein-Primakoff transformation and equation of motion in the theoretical model, we obtain the analytical magnon dispersion and the power threshold function. The power threshold for the three-magnon process is sensitive to the material properties. We find that the non-linearity is due primarily to incoherent magnon modes propagating in the thin film plane, while the modes propagating out of the film plane exist, but with much smaller occupation numbers.