Influence of oxygen partial pressure on structural, transport and magnetic properties of Co doped TiO2 films

TL;DR

This study investigates how varying oxygen partial pressure during deposition affects the structural, electrical, and magnetic properties of Co-doped TiO2 thin films, revealing phase transformations, oxygen vacancies, and property enhancements.

Contribution

It demonstrates the strong dependence of phase composition, conductivity, and magnetization of Co-TiO2 films on oxygen partial pressure during growth, highlighting the role of oxygen vacancies.

Findings

Presence of mixed anatase and rutile phases influenced by oxygen pressure

Oxygen vacancies correlate with increased conductivity and magnetization

Resistivity follows polaronic behavior with activation energies of 100-150 meV

Abstract

Thin films of Co-TiO2 are deposited on silicon and quartz substrates using Pulse Laser Deposition (PLD) process at various oxygen partial pressures ranging from 6.6 x 10-3 Pascals (Pa) to 53 Pa. Crystal structure, transport and magnetic properties of reduced CoxTi(1-x)O2 (0 <x< 0.03) thin films are investigated and are found to have a strong dependence on the oxygen partial pressure. X-ray diffraction (XRD) data reveals the presence of mixed phase material containing both anatase and rutile. However, these phases intertransform with the change in the oxygen partial pressure in the chamber during the growth of the films. X-ray Photoelectron Spectroscopy (XPS) shows no Co or CoO related peaks for samples with Co concentration up to x=0.03. However, the oxygen 1s peaks are asymmetric suggesting the presence of oxygen vacancies. The transport and magnetic measurements show a clear dependence on the concentration of oxygen vacancies. There is an enhancement in the electrical conductivity and the magnetization as more vacancies are created in the material. The resistivity as a function of temperature rho(T) follows the polaronic behavior and the activation energies obtained, ~100 to 150meV, are within the range that is typical for semiconducting materials.