  In this work we show the presence of a magnetoelectric coupling in
silicon-nitride gated Pt/Co/Pt heterostructures using X-ray photoemission
electron microscopy (XPEEM). We observe a change in magnetic anisotropy in the
form of domain wall nucleation and a change in the rate of domain wall
fluctuation as a function of the applied electric field to the sample. We also
observe the coexistence of in-plane and out of plane magnetization in Pt/Co/Pt
heterostructures in a region around the spin reorientation transition whose
formation is attributed to substrate surface roughness comparable to the film
thickness; with such domain configuration, we find that the in-plane
magnetization is more sensitive to the applied electric field than out of plane
magnetization. Although we find an effective magnetoelectric coupling in our
system, the presence of charge defects in the silicon nitride membranes hampers
a systematic electrostatic control of the magnetization.
