We report a combined experimental and theoretical study of the quasistatic hysteresis and dynamic excitations in large-area arrays of NiFe nanodisks forming a hexagonal lattice with the lattice constant of 390 nm. Arrays were fabricated by patterning a 20-nm-thick NiFe film using the etched nanosphere lithography. We have studied a close-packed (edge-to-edge separation between disks dcp = 65 nm) and an ultraclosed packed (ducp = 20 nm) array. Hysteresis loops for both arrays were qualitatively similar and nearly isotropic, i.e., independent on the in-plane external field orientation. The shape of these loops revealed that magnetization reversal is governed by the formation and expulsion of vortices inside the nanodisks. When we assumed that the nanodisks’ magnetization significantly decreases near their edges, micromagnetic simulations with material parameters
deter-mined independently from continuous film measu-rements could satisfactorily reproduce the hysteresis. Despite the isotropic hysteresis, significant in-plane anisotropy of the dynamic response of the ultraclose-packed array was found experimentally by the all-electrical spin-wave spectroscopy and Brillouin light scattering.
Dynamical simulations could successfully reproduce the difference between excitation spectra for fields directed along the two main symmetry axes of the hexagonal lattice. Simulations revealed that this difference is caused by the magnetodipolar interaction between nanodisks, which leads to a strong variation of the spatial distribution of the oscillation power both for bulk and edge modes as a function of the bias field orientation. Comparison of simulated and measured frequencies enabled the unambiguous identification of experimentally observed modes. Results of this systematic research are relevant both for fundamental studies of spin-wave modes in patterned magnetic structures and for the design of magnonic crystals for potential applications as, e.g., spin-wave guides and filters
In this paper, we present a detailed numerical micromagnetic study of the spin wave propagation in a thin magnetic film where several columns of circular antidots (holes) are cut out. We determine the transmission coefficient of such a system as the function of the spin wave frequency (transmission spectrum), and study the absorption and transmission frequency regions in dependence on the interdot distances and on the number of antidot columns. It turns out that already several antidot columns are sufficient to obtain nearly perfect gaps in the transmission spectrum of spin waves, so that already a system of a few such columns can be used as a very effective magnonic filter. Next, we establish a close relation between the transmission spectrum of our system and the spectrum of eigenmodes of the corresponding infinite antidot lattice. Finally, we demonstrate that transmission and absorption bands can be easily tuned (for the given antidot arrangement) by changing the external magnetic field. Importantly, the transmission spectrum exhibits a universal scaling when the external field is changed, when this spectrum is plotted as the function of the magnon wave vector.
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