Note: On the study of metal/oxide hybrid ferromagnets with magneto-optical techniques.

We analyze here the magneto-optical measurements of hybrid materials containing metallic and oxide ferromagnetic phases. We show that the magnetization curves obtained with this technique can be fairly different to those obtained with standard magnetometry techniques and cannot be representative of the contribution of each phase to the magnetization of the material, due to the very different optical properties of metals and oxides. However, a proper numerical analysis of the magneto-optical measurements allows estimating the fraction of each phase present in the material.