Origin of ferromagnetism in Cu-doped SnO2: A first-principles study

We investigate the magnetic properties of Cu-doped SnO2, which was reported recently in experiments to possess ferromagnetism at room temperature, by first-principles calculations. Our results show that the doped system prefers the antiferromagnetic state for only Cu substitution. The oxygen vacancies are more inclined to form on the sites nearest to Cu defects. However, only those oxygen vacancies away from Cu defects contribute to the ferromagnetism significantly. Our results reveal that Sn vacancies are much easier to form than oxygen vacancies for their much lower formation energy. Moreover, the Cu-doped system always prefers the ferromagnetic state in the presence of Sn vacancies. Therefore, the origin of ferromagnetism in Cu-doped SnO2 can be attributed to the magnetic mediation of Sn vacancies.