Brillouin light scattering measurements of spin wave dispersions in a saturated hexagonal array of interacting disks

Magnonic crystals (MCs), artificial materials with periodic modulation of the magnetic properties, have recently received large attention because of possibility of tuning the magnonic band structure and spin wave (SW) group velocity by an applied magnetic field. In this work, a hexagonal array of Permalloy interacting disks, having thickness of 20 nm, diameter of 370 nm and edge-to-edge separation of 20 nm, was fabricated by etched nano-sphere lithography. SW propagation has been investigated by Brillouin light scattering technique in the Voigt configuration, where the in-plane transferred wave-vector (k) is perpendicular to the external magnetic field. The SW dispersion has been measured first, when the samples are saturated along the direction of adjacent dots (k varies in ΓM’); then, when the sample is saturated perpendicular to the direction of adjacent dots (k varies in ΓM). The frequency and profiles of SW in these two different configurations were calculated through the dynamical matrix method [1], as a function of the wavevector. An example of band diagram (ΓM) is shown in Fig. 1, where experimental data (symbols) and calculations (lines) are shown. We have found an appreciable difference in the oscillation amplitude of the Fundamental mode in the two explored dispersions. This work was supported by the European Community’s Seventh Framework Programme (FP7/2007- 2013) under Grant Agreement n°228673 (MAGNONICS) and n°233552 (DYNAMAG).