Study on the formation of magnetic nanoclusters and change in spin ordering in Co-doped ZnO using magnetic susceptibility

Manipulation of spin ordering in oxides without extrinsic contribution is an important issue in current spintronics. This study introduced a mechanism to ascertain the formation of magnetic clusters and the magnetism of a Co-doped ZnO system by temperature-dependent magnetic susceptibility measurements. The measurements demonstrate the possibility of detecting tiny portions of Co clusters that could be created from Co oxides that were undetectable in X-ray diffraction or transmission electron microscopy. By fitting the magnetic susceptibility results, we were also able to ascertain that pure Co-doped ZnO showed a negative Curie–Weiss temperature, implying the existence of antiferromagnetic ordering; however, the Curie–Weiss temperature was gradually increased by intentional hydrogen introduction, with results suggesting that the antiferromagnetic ordering declined proportionally to the hydrogen contents by hydrogen mediation in Co–Co spin ordering and induced ferromagnetism. These results provide a useful methodological approach as well as experimental clues for identifying the origin of magnetism.