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

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 approximation. 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 which is of order one (not infinitesimal) even at nearly normal incidence. This lateral shift can be greatly enhanced by making the spin wave go through an array of well separated domain walls. The outgoing spin wave will not be appreciably attenuated by the scattering at the domain walls since the transmission coefficient is very close to one at nearly normal incidence. This effect may be very useful to control the spin waves in magnonic devices.

Reconfigurable Magnonic Crystals Based on Imprinted Magnetization Textures in Hard and Soft Dipolar-Coupled Bilayers

“…Analytical calculations and micromagnetic simulations have indicated that in periodic magnetization textures, the nonlocal dipole field arising from the finite film thickness leads to the formation of a band structure. 30 More recently, the role of the dipolar field has been also confirmed by Laliena et al 31 In this work, the authors have shown theoretically that Bloch domain walls, which are transparent to the SWs propagation when the dipolar interaction is neglected, are able to reflect SWs if the dipolar interaction is taken into account properly.…”