The interplay between dopants and oxygen vacancies in the magnetism of V-doped TiO2

TL;DR

This study uses density functional theory to explore how vanadium doping and oxygen vacancies influence the magnetic properties of TiO2, revealing that doping promotes ferromagnetism by increasing vacancy concentration and aligning spins.

Contribution

It demonstrates that V doping reduces oxygen vacancy formation energies and promotes ferromagnetic ordering in TiO2, a novel insight into defect-mediated magnetism.

Findings

V doping introduces magnetic V4+ species.

Oxygen vacancies are stabilized by V doping.

Ferromagnetic alignment occurs with both V dopants and oxygen vacancies.

Abstract

Density functional theory calculations indicate that the incorporation of V into Ti lattice positions of rutile TiO2 leads to magnetic V4+ species, but the extension and sign of the coupling between dopant moments confirm that ferromagnetic order cannot be reached via low-concentration doping in the non-defective oxide. Oxygen vacancies can introduce additional magnetic centres, and we show here that one of the effects of vanadium doping is to reduce the formation energies of these defects. In the presence of both V dopants and O vacancies all the spins tend to align with the same orientation. We conclude that V doping favours the ferromagnetic behaviour of TiO2 not only by introducing spins associated with the dopant centres but also by increasing the concentration of oxygen vacancies with respect to the pure oxide.