The Investigation of Oxygen Vacancies in Magnetic-Ferroelectric Heterostructures

M. Holcomb, West Virginia University (Principal Investigator)

A. Romero, West Virginia University (Co-Investigator)

In strongly correlated materials, vacancies are one of the most poorly understood factors, yet they can have dramatic effects on material performance. While oxygen vacancies often deplete material properties including magnetism and interfacial magnetoelectricity, those properties can be enhanced by these vacancies in others systems. In order to efficiently make use of this effect, the oxygen vacancies and their impact on other properties in a material must be accurately quantified. We propose to experimentally and theoretically investigate oxygen vacancies across magnetic La_xSr_1-xMnO₃ thin films adjacent to ferroelectric BaTiO₃ films and measure the effect on magnetoelectric coupling and layer-by-layer magnetization. Individually, these materials exhibit strong magnetic and ferroelectric properties, respectively, and both have been proposed for a wide array of applications. Analysis of x-ray absorption spectroscopy in total electron yield and fluorescence modes will allow study of atomic valences, magnetization and oxygen vacancies as the ferroelectric polarization direction is voltage controlled in epitaxial thin films. Theoretical calculations will provide insight into the effects of oxygen vacancies on the electronic, magnetic and ferroelectric properties of the pristine oxides as well as the heterostructures. Total energy calculations within density functional theory with Hubbard corrections to account for the lack of strong correlations in normal exchange correlation functions will be performed, allowing for the identification of the most probable configurations for the oxygen vacancies. Those optimal configurations will be used for further characterization of the electron band structure, possible magnetic induction, ferroelectricity, optical spectra and transport properties within the Landauer approximation. The information exchange between theory and experiment will provide a successful approach to understand the effect of oxygen vacancies within these materials and the joint effort will likely lead to novel methods to manipulate the oxygen presence in perovskite compounds.