Structure and Magnetic Properties of Co-doped (ZnO)₁₂ Clusters

Structure and magnetic properties of (ZnO)₁₂ clusters doped with one (monodoped) and two (bidoped) Co atoms are studied with first-principles method. Substitutional, exohedral, and endohedral doping are considered. Exohedral isomers are found the most favorable in both monodoped and bidoped clusters. Magnetic coupling between Co atoms is short-range. Magnetic coupling between Co atoms at the nearest neighbor is mainly governed by competition between direct Co-Co antiferromagnetic interaction and ferromagnetic interaction between two Co atoms via O atom due to strong p-d hybridization. We demonstrate that exohedral bidoped cluster favors ferromagnetic state, which has potential applications in nanoscale quantum devices.