Spin wave band structure in two-dimensional magnonic crystals

We present a combined experimental and theoretical study of the spin wave band structure in two-dimensional magnonic crystals consisting of square arrays of either circular permalloy dots (disks) or antidots (holes). The spin wave dispersion has been measured by means of Brillouin light scattering spectroscopy, spanning the wave vector over several Brillouin zones in the reciprocal space of the artificial crystals. The experimental data are satisfactorily interpreted thanks to band structure calculations carried out using the dynamical matrix method. In the case of the array of disks, the frequency dispersion of the different eigenmodes in any direction in the reciprocal space can be explained introducing the concept of a bidimensional effective wave vector. In the case of the antidot array, two families of propagating modes, having extended and localized character, exhibit bandgaps at Brillouin zone boundaries. The bandgap formation is discussed in terms of Bragg reflection as well as of the inhomogeneity of the internal magnetic field experienced by precessing spins. © Springer-Verlag Berlin Heidelberg 2013.