Scattering of spin waves by a Bloch domain wall: effect of the dipolar interaction

TL;DR

This paper investigates how the full dipolar interaction affects spin wave scattering by a Bloch domain wall, revealing non-zero reflection and lateral shifts that could be harnessed in magnonic device control.

Contribution

It introduces a perturbative approach to include the full dipolar interaction in spin wave scattering analysis, extending previous approximations that neglected these effects.

Findings

Reflection coefficient generally non-zero due to dipolar effects

Lateral shift of transmitted spin waves at normal incidence

Enhanced effects with multiple domain walls

Abstract

It is known that a Bloch domain wall in an anisotropic ferromagnet is transparent to spin waves. This result is derived by approximating the dipolar interaction between magnetic moments by an effective anisotropy interaction. In this paper we study the the scattering of spin waves by a domain wall taking into account the full complexity of the dipolar interaction, treating it perturbatively in the distorted wave Born approximation. Due to the peculiarities of the dipolar interaction, the implementation of this approximation is not straightforward. The difficulties are circumvented here by realizing that the contribution of the dipolar interaction to the spin wave operator can be split into two terms: i) an operator that commutes with the spin wave operator in absence of dipolar interaction, and ii) a local operator suitable to be treated as a perturbation in the distorted wave Born approximaton. We analyze the scattering parameters obtained within this approach. It turns out that the reflection coefficient does not vanish in general, and that the transmitted waves suffer a lateral shift even at normal incidence. This lateral shift can be greatlty enhanced by making the spin wave go through an array of well separated domain walls. The outgoing spin wave will no be attenuated by the scattering at the domain walls since the reflection coefficient vanishes at normal incidence. This effect may be very useful to control the spin waves in magnonic devices.