Origin of magnetism in undopedMoO2studied by first-principles calculations

Abstract

The electronic and magnetic properties of undoped ${\text{MoO}}_{2}$ have been studied using first-principles calculations within both the generalized gradient approximation (GGA) and $\text{GGA}+U$ method. The calculated results show that no magnetic moment forms in perfect ${\text{MoO}}_{2}$. For ${\text{MoO}}_{2}$ with Mo vacancies, the GGA results show some magnetic moments whereas the $\text{GGA}+U$ ($U=\ensuremath{-}1\text{ }\text{eV}$ for Mo) results indicate no magnetic moment forms. In the presence of type II O vacancies, both the GGA and $\text{GGA}+U$ results show no magnetic moment can form irrespective of the vacancies concentration. Nevertheless, the type I O vacancies always lead to formation of magnetic moments which couple ferromagnetically and should be the main origin of the magnetism in undoped ${\text{MoO}}_{2}$. The different structural properties and the corresponding charge-density redistribution behaviors of the two inequivalent types of oxygen vacancies are the origin of the different magnetic behaviors. For the magnetic interaction, the Ruderman-Kittel-Kasuya-Yoshida interaction and the superexchange mechanism cooperatively underlie the magnetism.