Tunable Snell's law for spin waves in heterochiral magnetic films

Abstract

Thin ferromagnetic films with an interfacially-induced Dzyaloshinskii-Moriya interaction (DMI) exhibit non-trivial asymmetric dispersion relations that lead to unique and useful magnonic properties. Here we derive an analytical expression for the magnon propagation angle within the micromagnetic framework and show how the dispersion relation can be approximated with a comprehensible geometrical interpretation in the k-space of the propagation of spin waves. We further explore the refraction of spin waves at DMI interfaces in heterochiral magnetic films, after deriving a generalized Snell's law tunable by an in-plane magnetic field, that yields analytical expressions for critical incident angles. The found asymmetric Brewster angles at interfaces of regions with different DMI strengths, adjustable by magnetic field, support the conclusion that heterochiral ferromagnetic structures are an ideal platform for versatile spin-wave guides.

Probing the Dzyaloshinskii-Moriya Interaction via the Propagation of Spin Waves in Ferromagnetic Thin Films

“…2(a). Similar results have been presented for spin waves propagation in different magnetic systems [45,46]. For instance, the generalized Snell's law describes the spin wave refracted at the domain wall in a chiral magnetic film in Ref.…”

Spin Waves in Thin Films and Magnonic Crystals with Dzyaloshinskii–Moriya Interactions

“…In particular, this numerical technique can be used to calculate the spectrum of spin waves, and when a DMI is present, it reveals different properties characteristic of these systems, such as the spin-wave asymmetry. In this context, simulations have successfully supported theoretical formulations [80,96,97,99,[132][133][134][135][136][137] and experimental measurements [72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87]138] on thin-film systems with a homogeneous DMI. A micromagnetic simulation is based on numerically discretizing the continuum description of the magnetic system into a mesh of magnetic moments whose arrangement depends on the discretization method.…”

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].…”