Study of structural, electronic and magneto-transport properties of functional magnetic oxides thin films and hetero-structures

In recent years, functional magnetic oxides have attracted huge attention among the materials scientists due to its prospects as magnetic semiconductors and utility in spintronics based devices. The work includes the study of structural, electronic and magneto-transport properties of Fe doped and undoped TiO2 based epitaxial thin film structures. It turns out that the evolution of the three phases; anatase, rutile and brookite of TiO2 as well as the magneli phase (TinO2n-1) strongly depends on the OPP and Fe doping concentration. We have investigated the electronic structure of the anatase phase films using resonant photoemission studies with the help of synchrotron source at Indus-1. Our study reveals that Fe ions hybridize with the oxygen vacancy induced Ti3+ defect states over a wide binding energy range. These films also reveal a finite density of states at the Fermi level indicating their metallic (degenerate semiconducting) behavior. Accordingly these anatase phase films reveal metallic behavior at high temperature; however, they show an upturn in resistivity at low temperature. Ab-initio calculations indicate that finite moment appears at Ti and Fe sites. We also observe that these films show magnetic ordering at room temperature and a Kondo like minimum in resistivity behavior. The transport behavior and band offset properties of the epitaxial TiO2/La0.7Sr0.3MnO3 hetero-structure (hybrid structure of ferromagnetic and semiconductor layer) are also investigated. The value for conduction band offset is estimated to be much lower than valence band offset, suggesting that transport is mainly dominated by electrons.