First-principles study of the effect of vacancies on magnetic properties ofZn1 − xCoxO thin films

Abstract

Due to the high solubility of Co in ZnO, the magnetic properties of Co-doped ZnO thinfilms have been extensively studied experimentally. Unfortunately, these results have led todiverse conclusions. To better understand the origin of the controversial experimentalfindings, we have carried out detailed theoretical studies, focusing on the roleof concentration and distribution of Zn and O vacancies on the magnetism ofZn1 − xCoxO thin films. We find that when Co atoms are substitutionally doped in ZnO thin filmswithout any defects, the magnetic coupling between Co atoms is intrinsicallyantiferromagnetic. The coupling, however, changes to ferromagnetic whensufficient oxygen vacancies are introduced. On the other hand, Zn vacanciesstabilize the antiferromagnetic coupling, in sharp contrast to that found inZn1 − xMnxO thin films. Our theoretical studies explain the origin of the different magnetic behaviorobserved experimentally.