First-principles study of the effect of Mn and point vacancies with different valence states on the magnetic properties of ZnO

Abstract

It is challenging to experimentally modulate the ferromagnetic properties of ZnO:Mn by point vacancies. Moreover, the magnetic source and magnetic mechanism of ZnO containing doped Mn and point vacancies, both with different valence states, have not been fully understood; using first principles can theoretically analyse this problem systematically. Therefore, in this study, the effects of different valence states of Mn and point vacancies on the magnetic properties of ZnO are calculated by first principles, revealing that ZnO:Mn has a lower formation energy and a more stable structure under oxygen-rich conditions than under zinc-rich conditions. Under oxygen-rich conditions, less Zn34Mn22+O35:VO0/1+/2+ and more Zn34Mn22+O36, Zn34Mn23+/4+O35:VO°, Zn33Mn22+O35:VZn0/1−/2−, and Zn33Mn23+/4+O36:VZn° are formed, facilitating the formation of a stable structure for the latter system compared to the others. The Zn33Mn22+O35:VZn° system not only possesses the lowest formation energy, but also the largest magnetic moment (10μB), indicating that a Zn vacancy allows the doping system to possess a high magnetic moment and also enhances the stability of the system. Therefore, Zn33Mn22+O35:VZn° is the most valuable of the systems studied. Analysis of the magnetic source and magnetic mechanism for this system revealed that the system possesses the magnetism and room temperature ferromagnetism, presents the characteristics of half-metallization, and that its magnetism is mainly derived from the itinerant electron and double exchange between O2p and Mn3d using holes as the medium. This is of great value for the design and preparation of new dilute magnetic semiconductors with high magnetic moments and high-Curie-temperature hole polarisation from 100 % injection sources.