Magnetic properties of transition-metal-dopedZn1−xTxO(T=Cr, Mn, Fe, Co, and Ni) thin films with and without intrinsic defects: A density functional study

Abstract

Theoretical calculations based on density-functional theory and generalized gradient approximation have been carried out in studying the electronic structure and magnetic properties of transition-metal-doped ${\text{Zn}}_{1\ensuremath{-}x}{T}_{x}\text{O}$ ($T=\text{Cr}$, Mn, Fe, Co, and Ni) $(11\overline{2}0)$ thin films systematically with and without intrinsic point defects (e.g., vacancies and interstitials), and as function of concentration and distribution of dopants and vacancies. Using large supercells and geometry optimization without symmetry constraint, we are able to determine the sites that metal atoms prefer to occupy, their tendency to cluster, the preferred magnetic coupling between magnetic moments at transition-metal sites, and the effect of intrinsic point defects on the nature of their coupling. Except for Mn atom, which distributes uniformly in ZnO thin films in dilute condition, transition-metal atoms occupying Zn sites prefer to reside on the surface and couple antiferromagnetically. The presence of native point defects has a large effect on the ground-state magnetic structure. In particular, $p$-type defects such as Zn vacancies play a crucial role in tuning and stabilizing ferromagnetism in ${\text{Zn}}_{1\ensuremath{-}x}{T}_{x}\text{O}$ thin films ($T=\text{Cr}$, Mn, Fe, and Ni), while $n$-type defects such as O vacancies or Zn interstitials greatly enhance the ferromagnetic coupling in ${\text{Zn}}_{1\ensuremath{-}x}{\text{Co}}_{x}\text{O}$ thin films. The present study provides a clear insight into the numerous conflicting experimental results on the magnetic properties of $T$-doped ZnO systems.