Ferromagnetic behavior of native point defects and vacancy-clusters in ZnO studied by first principle calculation

Abstract

The origin of room temperature ferromagnetism in undoped ZnO is still a question of debate. Experimental and theoretical findings are inconclusive as to the predominant contributor for the magnetic behavior of undoped ZnO. First principle calculation pseudopotential method was used to systematically determine the relaxed atomic geometry, the formation energies and the magnetic properties of the native point defects (vacancies, interstitials and antisites), and vacancy clusters (VZnVO, V-Zn - 2V(O)and 2V(Zn) - V-O) in ZnO. The results show that ZnO cells consisting of the V(Zn)and the O(i)have non-zero magnetic moments, energetically favoring ferromagnetic states and close-to-room-temperature Curie temperatures (294 K). V(Zn)and O(i)are also characterized by their low formation energies, in particular in the case of n-type (i.e. Fermi level close to the conduction band minimum) and O-rich conditions. The energy differences between the ferromagnetic state and anti-ferromagnetic state for V(Zn)and O(i)are larger than kT at room temperature but still relatively small (similar to 34 meV). Although V(Zn)and O(i)would contribute for the room temperature ferromagnetism, the ferromagnetism states would not be robustly stable for thermal excitation to the anti-ferromagnetic states.