Super-exchange interaction model in DMOs: Co doped TiO2 thin films

Abstract

This work presents a study of the structural, morphological, and magnetic properties of TiO2/Co thin films deposited by DC magnetron co-sputtering of Co and TiO2 targets, varying the concentration of the Co and TiO2 at room temperature. The formation of Co oxides binary phases was not observed. From XRD, μXRD, and Raman measurements were identified rutile and anatase phases, which evidence the formation of diluted magnetic oxide semiconductor (DMOs). Additionally, the TiO2 polymorphous and random location of Co ions are induced when the substrate is at room temperature, and in situ annealing process is applied. SEM, AFM, and MFM micrographs evidenced the formation of smaller grains (< 10 nm) in the surface without relationship with magnetic domains; values of the magnetic roughness were obtained between 199 and 442 pm. Magnetic measurements showed a ferromagnetic-like behavior with the appearance of a magnetic hysteresis loop. The hysteresis curves were associated with a combination of dipolar and super-exchange interactions between Co ions and mediated for oxygen ions based on Anderson’s model; this behavior was described from numerical simulations of isolated magnetic moments (Co atoms) diluted into a non-magnetic matrix (TiO2 structure). In this model, a random distribution of Co ions, contributing to dipolar magnetic interactions and super-exchange interaction, is considered, due to the hybridization sp3d2 of the Co–O bond and located randomly of Co ions. The experimental and theoretical results of this study present an explanation of ferromagnetic-like behavior for Co doped TiO2 thin films, as diluted magnetic semiconductor (DMS) for spintronic applications.