High-efficiency gigahertz frequency doubling without power threshold in thin-film Ni81Fe19

We demonstrate efficient second-harmonic generation at moderate input power for thin film Ni81Fe19 undergoing ferromagnetic resonance. Powers of the generated second-harmonic are shown to be quadratic in input power, with an upconversion ratio three orders of magnitude higher than that demonstrated in ferrites [W. P. Ayres et al., J. Appl. Phys. 27, 188 (1956)], defined as Delta P-2 omega/Delta P-omega similar to 4 x 10(-5) /W . P-omega, where Delta P is the change in the transmitted rf power and P is the input rf power. The second harmonic signal generated exhibits a significantly lower linewidth than that predicted by low-power Gilbert damping and is excited without threshold. Results are in good agreement with an analytic, approximate expansion of the Landau-Lifshitz-Gilbert equation. (C) 2013 AIP Publishing LLC.