Optical and Magneto-Optical Properties of Doped Oxides

This study aimed to understand the optical and magneto-optical properties of pure, transition metals doped, and tin and transition metals co-doped In2O3 thin films grown in various growth conditions, and aimed to investigate the role of the oxygen defect states in every situation. Indium oxide doped with magnetic transition metals is a promising material for spintronics. This study presents results on the magnetic, transport, optical and magneto-optical properties of thin films of pure and transition metal (Fe,Co) doped In2O3 investigated at different transition metal concentrations and at different growth conditions. The optical and magneto-optical measurements at low temperature confirmed the formation of the defect states associated with oxygen vacancies within the forbidden range of the optical band gap energy of In2O3 and located below the conduction band. The density of the donor states is tuned using the oxygen partial pressureto give oxygen vacancies or by doping with tin; this gives control over the carrier concentration in the system as well as affecting the magnetic properties. This study developed optical and magneto-optical systems and undertook the world’s first optical and magneto-optical measurements of In2O3. A new lab-based alternative technique to the Extended X-ray Absorption Fine Structurewas developed to identify the existence of magnetic nanoparticles in addition to provide the fraction and the contribution of these nanoparticles to the magnetisation and magneto-optical properties. The Maxwell-Garnett analysis of magnetic circular dichroism was used to obtain quantitative measures of the amount of defect phases present for Co metal. Similar to Maxwell-Garnett analysis, a new equation for Fe3O4 nanoparticles was developed in this study. This magneto-optical method was found to be more precise than EXAFS in determining the fraction and the contribution of nanoparticles to the total response of the system. However, these nanoparticles disappeared when thin films were co-doped with tin, indicating that doping with Sn not only introduced more carriers but also inhibited the growth of defect phases in semi magnetic semiconductor thin films. Finally, this study identified the origin of the magnetism in the class of magnetic oxides whereferromagnetism originated from the polarized electrons in localized donor states associated with the oxygen vacancy defect.