Heuristic Description of Magnetoelectricity of Cu₂OSeO₃

CuO₂SeO₃ is an insulating material that hosts topologically nontrivial spin whirls, so-called skyrmions, and exhibits magnetoelectric coupling allowing to manipulate these skyrmions by means of electric fields. We report magnetic force microscopy imaging of the real-space spin structure on the surface of a bulk single crystal of CuO₂SeO₃. Based on measurements of the electric polarization using Kelvin-probe force microscopy, we develop a heuristic description of the magnetoelectric properties in CuO₂SeO₃. The model successfully describes the dependency of the electric polarization on the magnetization in all magnetically modulated phases