Spin-wave beam propagation in ferromagnetic thin films with graded refractive index: Mirage effect and prospective applications

Abstract

Using analysis of iso-frequency contours of the spin-wave dispersion relation, supported by micromagnetic simulations, we study the propagation of spin-wave (SW) beams in thin ferromagnetic films through the areas of the inhomogeneous refractive index. We compare the transmission and reflection of SWs in areas with gradual and step variation of the SW refractive index. In particular, we show the mirage effect for SWs with narrowing SW beam width, and an application of the gradual modulation of the SWs refractive index as a diverging lens. Furthermore, we study the propagation of SWs in ferromagnetic stripe with modulated refractive index. We demonstrate that the system can be considered as the graded-index waveguide, which preserves the width of the SW beam for a long distance -the property essential for prospective applications of magnonics. arXiv:1707.09768v4 [cond-mat.mes-hall]

Graded index lenses for spin wave steering

“…To change the wave number and thus the index for the given wave frequency, we need to change the dispersion relation by varying one of the bulk material parameters, or film thickness [11][12][13][14][15] . We then need to choose an isotropic dispersion relation that enables a large change in k, and thus n. This requirement is satisfied in the dipolar-dominated regime, in the forward-volume geometry, where the magnetization is directed normal to the film plane.…”

“…However, these waveguides may suffer from losses/scattering in bends, and usually have a large spatial footprint. An alternative solution is to steer spin waves via a graded refractive index [11][12][13][14] , which smoothly alters the wave trajectory with minimal reflections 15 . To achieve a graded index for spin waves, one must gradually change a magnonic parameter on a length scale much smaller than the wavelength.…”

Direct observation of spin-wave focusing by a Fresnel lens

“…A main aspect of this confinement at relatively low frequencies is the formation of a caustic beam [10][11][12]. Additionally, it has been shown that refractive spin-wave optics can be realized [13][14][15][16][17][18][19].…”

The influence of exchange interaction and dynamic demagnetizing field on dispersion properties of Damon-Eshbach surface wave. Part 2. Dispersion relation.

“…Сегодняшняя тенденция к уменьшению размеров устройств обработки информации, использующих волновые процессы в ферритах, требует обращения к нанометровому диапазону длин магнитостатических волн [1][2][3][4]. В этом плане на смену довольно длинных (десятки и сотни микрон) дипольных волн [5][6][7][8] ожидается пришествие коротких (десятки и единицы нанометров) волн обменного характера [9,10], в том числе терагерцового диапазона, возбуждаемых импульсами фемтосекундной длительности [11][12][13] ( (3)…”