Generating Damon-Eshbach Spin Waves in Py using a Conducting Diffraction Grating

We have patterned silver hole arrays directly on top of uniform permalloy (Py) films. Typical Py and Ag film thicknesses are 25nm and 40 nm respectively; the holes in the Ag have a 500nm diameter and are patterned on a 1 micron lattice constant. We have measured resonant modes arising from a quasi-uniform microwave excitation field, applied in the plane of the sample, as a function of the in-plane external field and the in-plane field orientation relative to the principal axes of the array. Measurements were done using our broadband meanderline-based ferromagnetic resonance (FMR) spectrometer.\footnote{C. C. Tsai, J. Choi, S. Cho, B. K. Sarma, C. Thompson, O. Chernyashevskyy, I. Nevirkovets, and J. B Ketterson, Rev. of Sci. Instr. \textbf{80}, 023904 (2009).} In addition to a uniform FMR mode we observe satellite modes that correspond to the Damon-Eshbach spin waves\footnote{R. W. Damon and J. R. Eshbach J. Phys. Chem. Solids \textbf{19}, 308 (1961).} with wave vectors having Fourier components of the reciprocal lattice of the silver array. Hence, in an otherwise uniform magnetic film the silver array acts as a \textit{diffraction grating} which excites spin waves with k $\ne $ 0 from the dynamic k $\approx $ 0 microwave magnetic field. The observed spin wave angular dispersion is in excellent agreement with a magnon dispersion relation for spin waves in a uniform film given by Kriesel et al.\footnote{A. Kreisel, F. Sauli, L. Bartosch, and P. Kopietz, Eur. Phys. J. B \textbf{71}, 59 (2009).}