Observation of higher-order gyrotropic modes and energy transfer in cylindrical ferromagnetic nanodots-based square lattices

Abstract

We investigated and reported on a wide variety of gyrotropic modes in both isolated thick cylindrical magnetic vortices and lattices of such magnetic vortices arranged in square-lattice structures. In significantly thicker magnetic vortices, we see a higher-order flexure modes in addition to the uniform gyrotropic modes. We thoroughly examined the variation of the frequency and intensity of these modes with the thickness of the magnetic nanodots forming a vortex. We specifically looked at how the thickness, diameter, and aspect ratio of a single magnetic vortex and magnetic vortex lattice in various configurations affect the mode frequencies. When the magnetic vortex at the center is excited by an a.c. spin-polarized current with an excitation frequency equal to the collective gyrotropic frequencies of the lattice, we discuss the dynamics of the transfer of magnetic energy at three high symmetry points of the three-dimensional lattice of Permalloy nanodots with a vortex structure. The energy transmission in these lattice systems is estimated using the power and phase distributions for such configurations. Lattice configurations with substantially thicker nanodots consisting of uniform modes and higher-order flexure modes in the Eigen spectrum have transmission with uniform modes in specific directions and suppression in others, acting as a magnonic filter, and no transmission at all with higher-order modes. Such magnonic vortex lattice structures seek to improve the future prospects of technology and provide emerging applications in information processing devices, magnonic filters, three-dimensional waveguides, and magnonic crystals.