  In this paper we extend the micromagnetic theory of magnetostatic surface
waves in insulating ferromagnetic thin films to include the applied electric
field effects. We start by identifying the two main effects on the dispersion
relation: the first one is of relativistic nature and emerges as a consequence
of the Ahronov-Casher effect, while the second one is a consequence of the
electric field induced symmetry breaking operating at the level of magnetic
exchange interactions. We support our theory by comparing its predictions with
experimental data on ittrium iron garnet thin films taken from the literature.
The main result is to evidence the limitations of using the same value of the
applied electric field to address both effects and to emphasize that crystal
symmetry breaking due to the applied electric field brings about the
contributions of the crystal field and determines different amplitudes for the
two effects.
