Magnetic properties of isolated Re ion and Re-Re complex in ZnO studied by GGA +U approach

Magnetic properties of Re substituting for the divalent Zn ions and impurity pairs in wurtzite and zinc blende ZnO are analyzed by employing the Generalized Gradient Approximation with the +U corrections. The +U term applied to d(Zn), p(O), and d(Re) orbitals stabilizes spin polarization of Re. Re impurity introduces a defect level located in the band gap, and Re2+ generates the local spin 5/2 in both wurtzite and zinc blende structures. Magnetic coupling of Re-Re pairs as a function of distance between the defects, their relative orientation, and the charge state was calculated. All magnetic coupling between impurities is antiferromagnetic and due to an intermediate O atom via strong d(Re)-p(O) hybridization between Re and O states. The defect states and magnetic moments come from d(Re) with a contribution of p(O) orbitals of the O nearest neighbors of Re. The results show that the Re-doped wurtzite ZnO may be a new type of magneto-optical materials with a great promise.