Transition metal doping engineered octagonal ZnO monolayer magnetic properties

The two-dimensional (2D) topology assisted direct exchange interaction induced magnetic properties are in principle can be engineered for applications. To this endeavor, density functional theory (DFT) based first principle calculations are performed to study doping of 3d transition metal (TM) in graphene-like hexagonal (h)- and recently proposed octagonal (o)-ZnO monolayers. The o-ZnO monolayer shows high thermal stability (up to 1300 K) along with high energetically doping preference for 3d TM. By virtue of Hund's rule, the TM doped localized magnetic moment of system can be tuned up to 5 mu(B) based on the choice of TM and type of doping. The general trend of increase in charge transfer and doping stability with decrease in atomic number is found, the exceptions are of Cr and Mn. Doping of Mn, Cr and Fe shows high magnetic moment, among them doping of Fe is energetically most stable. Incorporation of U parameter changes electronic structure landscape significantly but relative variation in magnetic properties remained similar. High doping concentration of Fe prefers antiferromagnetic exchange coupling in order to minimize the system energy while mixing of interstitial along with substitutional doping leads to high magnetic moment as a result of topologically assisted direct exchange interaction. The substitutional doping of TM (except Ti and V) is predicted to be useful for spintronic applications, wherein with the exception of Co, o-ZnO monolayer is found to be a superior candidate than h-ZnO monolayer.