We present a combined experimental and theoretical study of the dynamic excitation spectra in arrays of 20 nm thick NiFe disks arranged into a hexagonal lattice. The disks, fabricated using the etched nano-sphere lithography, have diameter of 370 nm and an edge-to-edge separation of 20 nm. Longitudinal hysteresis loops measured by magneto-optic Kerr effect reveal that the magnetization reversal for both arrays is governed by the formation and expulsion of vortices inside the nanodisks and is nearly independent on the in-plane external field direction. Spin wave spectra were measured complementary by the all-electrical spin-wave spectroscopy and Brillouin light scattering, for two different in-plane direction of the applied magnetic field, i.e. H parallel and perpendicular to the disks rows. Dynamical simulations have been performed by means of Micromagus and the dynamical matrix methods (DMM), obtaining a good agreement with the experimental results. We found both bulk modes, concentrated in central regions of the nanodisks, and edge modes located near the borders of the nanodisks. Starting from the positive saturation we notice that for both the field orientation the frequency of all the modes decreases in an almost linear way, except for the edge mode. Simulations reveal that both bulk and edge modes are strongly affected by the external field orientation, due to the anisotropy of the magnetodipolar interaction between the disks. In particular, the edge mode is absent when H is directed along the nanodisks rows, due to the nearly complete cancellation of the self-demagnetizing field of a nanodisk by the stray field of its nearest neighbors. Results of this systematic research is relevant for the fundamental studies of spin wave modes in patterned magnetic structures in general, and for the design of magnonic crystals for numerous potential applications such as spin-wave guides and filters. 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).
Magnetic field dependence of spin waves in ultra-close packed NiFe disks arranged into a hexagonal lattice
MONTONCELLO, Federico;GIOVANNINI, Loris
2013
Abstract
We present a combined experimental and theoretical study of the dynamic excitation spectra in arrays of 20 nm thick NiFe disks arranged into a hexagonal lattice. The disks, fabricated using the etched nano-sphere lithography, have diameter of 370 nm and an edge-to-edge separation of 20 nm. Longitudinal hysteresis loops measured by magneto-optic Kerr effect reveal that the magnetization reversal for both arrays is governed by the formation and expulsion of vortices inside the nanodisks and is nearly independent on the in-plane external field direction. Spin wave spectra were measured complementary by the all-electrical spin-wave spectroscopy and Brillouin light scattering, for two different in-plane direction of the applied magnetic field, i.e. H parallel and perpendicular to the disks rows. Dynamical simulations have been performed by means of Micromagus and the dynamical matrix methods (DMM), obtaining a good agreement with the experimental results. We found both bulk modes, concentrated in central regions of the nanodisks, and edge modes located near the borders of the nanodisks. Starting from the positive saturation we notice that for both the field orientation the frequency of all the modes decreases in an almost linear way, except for the edge mode. Simulations reveal that both bulk and edge modes are strongly affected by the external field orientation, due to the anisotropy of the magnetodipolar interaction between the disks. In particular, the edge mode is absent when H is directed along the nanodisks rows, due to the nearly complete cancellation of the self-demagnetizing field of a nanodisk by the stray field of its nearest neighbors. Results of this systematic research is relevant for the fundamental studies of spin wave modes in patterned magnetic structures in general, and for the design of magnonic crystals for numerous potential applications such as spin-wave guides and filters. 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). I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
