Enhanced defect-mediated ferromagnetism in Cu2O by Co doping

In this work an extensive characterization of Co doped Cu2O thin films grown by electrochemical deposition is presented. The doped films showed ferromagnetic behavior, with impressive Curie temperature up to 700 K. Undoped samples also presented magnetic moments at room temperature, but much reduced when compared to doped ones. The observed magnetism in undoped and doped samples was taken as an indicative of a defect-mediated ferromagnetism. Moreover, the sample magnetization was reduced as a consequence of a decreasing in defect density due to thermal annealing. Polarization-dependent X-ray absorption measurements demonstrated that oxygen derived states are the source of the observed magnetic moment and its magnetic dichroism depends on the amount of point defects. Structural, optical and electrical characterization provides information that confirms the incorporation of Co atoms in the Cu2O lattice, without the formation of secondary segregated Co phases. In addition, Electron Paramagnetic Resonance and Glow Discharge Optical Emission Spectroscopy measurements reject the existence of contaminants in the films, dismissing them as the source for the observed magnetism. Computational calculations have shown that Co doping shall locally increases the amount of defects, such as interstitial O, leading to highly oxidized regions from where the unpaired spin arises. This situation generates a picture similar to the magnetic polaron theory, but with the dopant ion pinning the defects.