  The spin wave spectra of multiferroic BiFeO3 films is calculated using a
phenomenological Landau theory that includes magnetostatic effects. The lowest
frequency magnon dispersion is shown to be quite sensitive to the angle between
spin wave propagation vector and the Neel moment. Since electrical switching of
the Neel moment has recently been demonstrated in this material, the
sensitivity of the magnon dispersion permits direct electrical switching of
spin wave propagation. This effect can be used to construct spin wave logical
gates without current pulses, potentially allowing reduced power dissipation
per logical operation.
