Magnetic interactions in the Zn-Co-O system: tuning local structure, valence and carrier type from extremely Co doped ZnO to ZnCo(2)O(4)

We have investigated the relation between local structure, valence and carrier type with magnetism in the Zn-Co-O system. Thin films ranging from wurtzite Zn(1−x)Co(x)O (Co:ZnO) to ZnCo(2)O(4) spinel were grown on c-sapphire substrates. On the one hand, the unprecedented doping of x = 0.6 Co in ZnO enables to study the structural and magnetic properties well-above the coalescence limit. On the other hand, the ZnCo(2)O(4) spinel provides a p-type environment. We find a strong correlation between local structure, valence and carrier type throughout the Zn-Co-O system. In contrast to earlier publications neither 60% Co:ZnO nor ZnCo(2)O(4) exhibit any sign of ferromagnetic order despite of the high concentration of magnetic ions and a p-type carrier background. Instead, antiferromagnetic exchange is found to be the predominant magnetic interaction in the Zn-Co-O system.