Controlling magnon propagation and frequency gap through the fan angle of a sinusoidal bias field

We investigate through micromagnetic simulations the spin-dynamics of a ferromagnetic film to which a sinusoidal magnetic field is applied with fixed magnitude and variable fan angle ΘF. At equilibrium, the magnetization relaxes in a likewise sinusoidal distribution with an amplitude depending on ΘF. We illustrate in detail how the dispersion curves and the frequency gap at zone boundary vary with ΘF, discussing the functional behavior and the correlation to the potential energy density. We also discuss the extent and limits to which the Kittel formula can be used in computing the resonance frequencies even for sinusoidal magnetizations, definitely far from being uniform. In conclusion, we demonstrate that it is possible to achieve full control on magnon propagation through ΘF as a sole degree of freedom. This allows to keep the field magnitude constant and small, reducing energy dissipation at a minimum, with positive implications for dissipationless magnon-devices