Tuning Low-Spin to High-Spin Mn Pairs in 2-D ZnO by Injecting Holes

We have performed an ab initio theoretical investigation of substitutional Mn atoms in planar structures of ZnO, viz., monolayer [(ZnO)₁] and bilayer [(ZnO)₂] systems. Due to the 2-D quantum confinement effects, in those Mn-doped (ZnO)₁ and (ZnO)₂ structures, the antiferromagnetic (AFM) coupling between (nearest neighbor) Mn_Zn impurities have been strengthened when compared with the one in ZnO bulk systems. On the other hand, we find that the magnetic state of these systems can be tuned from AFM to FM by adding holes, which can be supplied by a p-type doping or even photoionization processes. Whereas, upon addition of electrons (n-type doping), the system keeps its AFM configuration.