A study on defect formation and magnetic properties of Ni doped ZnO nanowires

In the paper, formation and ionization energies of defects and ferromagnetism in Ni doped ZnO nanowires (NW) are investigated by the first principles. Ni impurity has lower formation energies in surface sites, which indicates that Ni impurity occupies preferably surface sites of NW. The transition energy levels of Ni defect are located at 0.33 and 1.71 eV. It is found that IZn(oct) and VO(B) are deep donor, VZn(B) and IO(oct) are deep acceptor. Ferromagnetic (FM) and antiferromagnetic (AFM) coupling are investigated by 9 different configurations, which indicates that FM coupling between Ni atoms is more stable than AFM coupling. The FM stability can be explained by Ni 3d energy level coupling. In addition, impact of the vacancies [VO (B) and VZn (B)] and interstitials [IO (oct) and IZn (oct)] on FM coupling is also investigated. It is found that magnetic moment of Ni can be tuned by these defects.