Modulating magnetism of ZnO:C with vacancy and substitution

We investigate magnetic properties of C-doped ZnO (ZnO:C) systems in the presence of defects such as O and Zn vacancies and substitution of Li and Al for Zn. Specifically, we use density functional theory to calculate electronic structures, local magnetic moment, polarization energy, etc., for these material systems. We find that the magnetic moment at a C atom in ZnO:C can be suppressed by the presence of an oxygen vacancy and enhanced by the presence of a Zn vacancy, and depends sensitively on the distance between the C atom and such a vacancy. Our results provide an explanation of the experimental observation that the C-induced magnetic moment in ZnO:C varies widely, from 1.3 _B to 3.0 _B. We also show that Lithium and Aluminum implantations in ZnO:C can effectively tailor the magnetic moment and ferromagnetism, regardless of the distance between the implanted atoms and the C atoms. In particular, our results indicate that Curie temperature in a ZnO:C system can potentially be increased by Al implantation.