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

 

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 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 the 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 1 at nearly normal incidence. This effect may be very useful to control the spin waves in magnonic devices.