Absorbing boundary layers for spin wave micromagnetics

Abstract

Micromagnetic simulations are used to investigate the effects of different absorbing boundary layers (ABLs) on spin waves (SWs) reflected from the edges of a magnetic nano-structure. We define the conditions that a suitable ABL must fulfill and compare the performance of abrupt, linear, polynomial and tan hyperbolic damping profiles in the ABL. We first consider normal incidence in a permalloy stripe and propose a transmission line model to quantify reflections and calculate the loss introduced into the stripe due to the ABL. We find that a parabolic damping profile absorbs the SW energy efficiently and has a low reflection coefficient, thus performing much better than the commonly used abrupt damping profile. We then investigated SWs that are obliquely incident at 26.6, 45 and 63.4 degrees on the edge of a yttrium-iron-garnet film. The parabolic damping profile again performs efficiently by showing a high SW energy transfer to the ABL and a low reflected SW amplitude.Comment: Journal of Magnetism and Magnetic Materials, 201

Goos-Hänchen effect of spin waves at heterochiral interfaces

“…Magnetic parameters of permalloy are used in simulations: M s = 8 × 10 5 A/m and A = 13 pJ/m. In the dynamic simulations, a Gilbert damping constant of α = 0.001 is used to ensure a long-distance propagation of the spin-wave beams, and absorbing boundary conditions are adopted to avoid the spin-wave reflection by film edges [32]. An external field µ 0 H 0 = 1 T along +ŷ is applied to saturate the in-plane magnetization.…”

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

“…Finally, after a sufficiently long time τ , a 2D Fourier transform in space and time variables is performed in order to obtain the spin-wave spectrum. To avoid noise in the spectrum caused by the reflection of the spin waves at the sample edges, it has been shown that using a strong damping towards the sample edges minimizes this effect [146]. Alternatively, it is also possible to use periodic boundary conditions.…”

Control of Dynamics in Weak PMA Magnets

“…The damping parameter is reduced from α = 1 (used for static simulations) to a smaller value of 0.08 for NdCo x and 0.01 for Permalloy [36]. For Figure 8: (i) the surface of the working space was changed from squared (see above) to rectangular: 5.62 × 0.96 µm 2 ; (ii) the periodic boundary conditions were suppressed; (iii) an enveloping area with increased damping at the edges of the working area was used to simulate infinite extent samples (absorbing boundary conditions) [56]. The magnetic field was applied on a single row spin, transversal to the wavevector, → k in order to take advantage of the absorbing boundary conditions (the cell 512th in Figure 8).…”