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

SnO₂ thin films of ~ 150 nm thicknesses were deposited on quartz substrate by pulse laser deposition technique and annealed at 600–900 °C for 1 h 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 473 cm⁻¹, 627 cm⁻¹ and 766 cm⁻¹ corresponding to the tetragonal rutile phase of SnO₂, two IR active Raman bands and one Raman forbidden mode were also observed at 500 cm⁻¹, 690 cm⁻¹ and 544 cm⁻¹ respectively. The dc resistivity measurements in the temperature range of 297–400 K 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. - Highlights: • Preparation of SnO₂ thin films using pulse laser deposition technique • Structural analysis of as prepared and annealed thin films • Dielectric properties for all the annealed samples with frequency at room temperature • Role of grains and grain boundaries in the conduction process • Room temperature M–H curves for post annealed SnO₂ thin films