Origin of ferromagnetism in Ni-doped SnO2: First-principles calculation

Abstract

The effects of Ni dopants and O vacancies on the electronic structure and magnetic properties of Ni-doped SnO2 are studied using the first-principles density functional calculation. Both of generalized gradient approximation (GGA) and GGA+U calculations show that substitutional Ni atoms at Sn sites cannot induce magnetic moment in Ni-doped SnO2 without O vacancy. O vacancies prefer to locate near Ni atoms and induce the magnetic moments at Ni atom and its nearest O atoms. Moreover, O vacancies in a chain connecting two Ni atoms of large distance can lead to a long-range ferromagnetic (FM) coupling between the two Ni atoms. The strength of coupling calculated by GGA+U is about triple that calculated by GGA. The spin density distribution shows that the long-range FM coupling between two Ni atoms can be explained in terms of the bound magnetic polaron model.