Magnetism of (Zn,Co)O thin films probed by x-ray absorption spectroscopies

We report on the electronic and magnetic properties of Co-doped ZnO thin films investigated by x-ray absorption spectroscopies and element selective magnetometry. For a low Co concentration (around 5%), we evidence a paramagnetic phase clearly correlated to Co2+ ions substituted to Zn in the ZnO matrix. For higher Co concentrations (around 25%), we demonstrate the coexistence of both paramagnetic and ferromagnetic phases. The use of advanced element and orbital selective techniques allows us through the distinct spectral signature of Co in ionic or metallic states to assign the ferromagnetic phase to the presence of Co in a metallic state as a consequence of Co metal clustering in our films.