Date of Completion

2-10-2016

Embargo Period

2-10-2016

Keywords

Fe3O4, Epitaxial growth, Verwey transition, Thin film

Major Advisor

Boris Sinkovic

Associate Advisor

William A. Hines

Associate Advisor

Joseph I. Budnick

Field of Study

Physics

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

This work describes the synthesis of high quality of epitaxial Fe3O4 ultrathin films and characterization of the structure, transport, and magnetic properties of both single layer and multilayer epitaxial Fe3O4 ultrathin films.

The surface structures of magnetite (Fe3O4) thin films have been extensively investigated by the surface science community while the bulk properties have been studied by material science and condensed matter community. In this thesis, we tried to bridge the gap between the two studies to explore the effect of the surface and interface structure on the transport and magnetic properties of ultrathin magnetite films that has not been done before. Understanding these effects is becoming critical for improving the performance and properties of spintronics devices.

In this work, a comprehensive study has been done to explore the effect of the thickness and oxygen stoichiometry on the structure, magnetic, and transport properties of the epitaxial Fe3O4 ultrathin films grown on MgO (0 01) substrates. The optimized conditions have been established for the growth of high-quality Fe3O4 epitaxial ultrathin films, which are formed within a narrow range of oxygen pressure deposition window.

The epitaxial Fe3O4 ultrathin films have been grown by molecular beam epitaxy (MBE) under ultra-high vacuum (UHV) on MgO (001) single-crystalline substrates. The crystallographic and electronic structures of the films were characterized using low energy electron diffraction (LEED) and x-ray photoemission spectroscopy (XPS), respectively. The quality (stoichiometry) of the epitaxial Fe3O4 ultrathin films was judged by magnetic measurements of the Verwey transition, along with complimentary XPS spectra. It was observed that under the same growth conditions, the stoichiometry of ultrathin films under 10 nm transform from the Fe3O4 phase to the FeO phase. In this work, a phase diagram of thickness and oxygen pressure has been constructed to explain the structural phase transformation. It was found that high-quality magnetite films with thicknesses ≤ 20 nm formed within a narrow range of oxygen pressure and that it varies with the thickness, which has not been reported previously. An optimal and controlled growth process is a crucial requirement for the accurate study of the magnetic and electronic properties of ultrathin Fe3O4 films and their application.

Download

Share

COinS