Abstract
Based on first-principles calculations, the coexistence of Ti vacancies (VTi) and O vacancies (VO) is first considered to study the origin of the ferromagnetic ordering in undoped rutile TiO2. The calculations show that VO can induce local magnetic moments in TiO2, however, the ferromagnetic (FM) exchange interaction of two VO is not strong enough to induce room-temperature (RT) ferromagnetism on their own in undoped TiO2. The FM coupling between two VTi is about four times stronger than that between two VO. More importantly, the FM coupling between two VTi is further enhanced after VO is introduced. Our results indicate that the electrons induced by VO mediate the long-range FM exchange interaction between two distant VTi. This maybe the ferromagnetism mechanism in undoped TiO2: VTi produce local moments while the electrons induced by VO mediated the long-range FM exchange interaction. The results are in excellent agreement with the experimental evidences that VO alone cannot induce RT ferromagnetism while VO can promote the ferromagnetic ordering in undoped TiO2.
Highlights
Following the report of ferromagnetism in undoped HfO2 thin films of Venkatesan et al.,[1] many research groups pay attention to investigate the origin of so called “d0” ferromagnetism
The calculations show that VO can induce local magnetic moments in TiO2, the ferromagnetic (FM) exchange interaction of two VO is not strong enough to induce room-temperature (RT) ferromagnetism on their own in undoped TiO2
Our results indicate that the electrons induced by VO mediate the long-range FM exchange interaction between two distant VTi. This maybe the ferromagnetism mechanism in undoped TiO2: VTi produce local moments while the electrons induced by VO mediated the long-range FM exchange interaction
Summary
Following the report of ferromagnetism in undoped HfO2 thin films of Venkatesan et al.,[1] many research groups pay attention to investigate the origin of so called “d0” ferromagnetism. “d0” ferromagnetism has been observed in undoped TiO2,2–6 In2O3,2,7 ZnO,[7,8] and SnO27,9 films, nanoparticle and nanoribbons. Most experimental evidences indicate that the RT ferromagnetism in these undoped oxides is induced by VO.[2–7,9] On the other hand, first-principles calculations indicate that local magnetic moments are due to cation vacancies in CaO,[10] HfO2,11 ZnO,[12] SnO2,13 and TiO214 while VO cannot induce local moments. Both experimental evidences[2–9] and theoretical studies[10–14] revealed that the ferromagnetism is induced by intrinsic defects in undoped oxides. Whether cation vacancy or anion vacancy defect contributes to the RT ferromagnetism is still controversial
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