  In this letter, the authors present a study of the energetics and magnetic
interactions in Fe doped ZnO clusters by ab-initio density functional
calculations. The results indicate that defects under suitable conditions can
induce ferromagnetic interactions between the dopant Fe atoms whereas
antiferromagnetic coupling dominates in a neutral defect-free cluster. The
calculations also reveal an unusual ionic state of the dopant Fe atom residing
at the surface of the cluster, a feature that is important to render the
cluster ferromagnetic.
