Isotropic strains tuned hole-mediated ferromagnetism in nitrogen-doped ZnO

• Formation energies and energy levels of NO in ZnO can be tuned by isotropic strains.
• The magnetic moments and the interactions between NO can be tuned by strains.
• Tensile strains favored FM coupling between NO, while compressions stabilize AFM.

The effects of isotropic strains on the doping and magnetic properties of nitrogen doped ZnO system are investigated by density functional theory calculations. The formation energy and the ionization energy of NO in ZnO are calculated each as a function of strains. We show that compressive strains favor the solubility of nitrogen in ZnO, while the tensile ones render the acceptor level shallower. The shallower energy level means that the acceptor wave function becomes delocalized, which is favorable for mediating long-range coupling between defects. The effects of strains on the coupling strength between two NOs are also studied. Our calculations indicate that the ferromagnetic coupling in ZnO:N can be enhanced by applying tensile strains, but weakened by compressive strains. These manipulation trends of the magnetic couplings under stains are interpreted by the band coupling models.