Growth of Thin Films by Pulsed Laser Deposition for Applications in Spin Transport Electronics
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
This thesis presents the results of the growth and characterisation of three separate compounds, all of which have been deposited on sapphire, silicon and SrTiO₃ substrates using the pulsed laser deposition technique. The first material studied was cobalt doped titanium dioxide, with initial growths being performed using un-doped TiO₂ targets. These films were used to optimise the growth parameters before introducing Co:TiO₂ targets in later growths, where targets with cobalt concentrations of 3, 6 and 12 % were used to grow Co:TiO₂ thin films. The Co:TiO₂ films were found to be highly oriented, with single phase rutile appearing on the sapphire substrates and single phase anatase being deposited on the SrTiO₃ substrates. The films were optically transparent across the visible region, with optical gaps greater than 3 eV. The films showed ferromagnetic behaviour at 10 K and 300 K, with only small reductions in the saturation moments being observed at the higher temperature, indicating the films had a Curie temperature around 600 K. The second material studied was the half-metallic double perovskite, Sr₂FeMoO₆. In particular the affect of deposition pressure and substrate choice on the structural and magnetic properties of the films was studied. We found the saturation moments of the films to increase dramatically when deposited at 850 ℃, compared to films deposited at 650 ℃. The choice of substrate was also observed to have a large affect on the magnitude of the saturation moments, with films deposited on silicon having the largest observed moments. Finally a small study was performed on the oxygen deficient SrFeO₃-δ, where we managed to grow thin films with varying oxygen concentrations through a combination of altering the oxygen pressure during growth and performing post growth annealing. We found that post growth annealing in oxygen was more effective at introducing oxygen into the films while still maintaining a high crystalline quality.