Annealed SnO2 thin films: Structural, electrical and their magnetic properties

Abstract

SnO2 thin films of ~150nm thicknesses were deposited on quartz substrate by pulse laser deposition technique and annealed at 600–900°C for 1h with a variation of 100°C per sample. The X-ray diffraction patterns show that as deposited SnO2 thin film was completely amorphous while annealed SnO2 thin films were randomly oriented, polycrystalline in nature and correspond to the rutile phase. The average crystallite size estimated using Scherrer and Williamson–Hall equations was found to increase with annealing temperature. In addition to the three fundamental Raman peaks at 473cm−1, 627cm−1 and 766cm−1 corresponding to the tetragonal rutile phase of SnO2, two IR active Raman bands and one Raman forbidden mode were also observed at 500cm−1, 690cm−1 and 544cm−1 respectively. The dc resistivity measurements in the temperature range of 297–400K show semiconducting behavior of all the annealed thin films. Room temperature dielectric properties of all the samples show dispersion which is explained in the light of Koop's theory based on Maxwell–Wagner two layer models. The dielectric parameters: real part of dielectric constant, dielectric loss and ac conductivity show their maximum value for SnO2 film sample annealed at 600°C. The dielectric loss shows anomalous behavior and exhibits relaxation peaks (Debye peaks) at lower and middle frequencies. Complex impedance plots (Nyquist plots) for annealed SnO2 thin films show two well-resolved semicircles corresponding to two different electrical transport mechanisms which stand for grain and grain boundary. It is observed that the contribution of grains in the conduction process starts dominating over the grain boundary with the increase in annealing temperature. From a magnetic hysteresis loop, it is clear that all the single phase SnO2 thin films annealed at different temperatures are ferromagnetic at room temperature and the value of saturation magnetization shows its maximum for the film annealed at 600°C.