Observation of excess polar magneto-optical Kerr effect signals in asymmetric Co/Tb-multilayers

We study the magneto-optical properties of asymmetric Co/Tb-multilayers that are designed to exhibit considerable Dzyaloshinskii-Moriya interaction (DMI) and low levels of effective perpendicular magnetic anisotropy. Accordingly, non-uniform magnetization states can occur in these films at intermediate magnetic field strengths, which cause a corresponding net magnetization reduction. Simultaneously, we observe an excess polar magneto-optical Kerr effect (MOKE) signal that increases beyond its value at saturation and is fully anticorrelated with the magnetization in its field dependency. We also find a very strong wavelength dependence of this excess polar MOKE signal that is very different from the MOKE behavior at saturation. All experimental data can be quantitatively explained by an additional polar MOKE mechanism that is associated with magnetic non-uniformities, such as, for instance, skyrmions, which have already been demonstrated to generate topological MOKE in certain compounds.