We report the experimental observation of band gaps in a synthetic nanostructured magnonic crystal composed of two different magnetic materials. The sample, in the form of a one-dimensional periodic array comprising alternating Permalloy and cobalt nanostripes, has been fabricated using advanced lithographic techniques. Dispersion relations of spin waves in the magnonic crystal have been mapped by Brillouin spectroscopy. The center frequency and width of the band gaps observed are tunable by an applied magnetic field. Dispersion relations calculated based on the finite element method accord with the measured data.

We investigate theoretically the lowest-frequency spin waves in one-dimensional periodic arrays of alternating cobalt and permalloy nanostripes to analyze their recently measured first band gap parameters. Based on insights from numerical calculations, we formulate simple equations relating center frequencies and widths of the first band gaps of these magnonic crystals to their geometric and magnetic parameters. Analytical calculations based on these equations accord well with both the measured and the numerically generated size-dependences of the band gap parameters. Our approach permits the easy and convenient evaluation of the band gap parameters of bicomponent magnonic crystals comprising one-dimensional arrays of nanostripes of alternating magnetic materials.