Influence of the grain's morphology and their distribution on surface, electronic and magnetic properties of Sn_(1-x)Co_xO_2 nanocrystalline Diluted Magnetic Semiconductors

摘要

With a view to understand not only the nanosize dependent properties of microstructure and electronic properties, but also to study the correlations between the surface effects associated with the magnetic nano-particles, especially consequent changes in the electronic structure and associated phonon confinement effect on nanocrystalline Sn_(1-x)Co_xO_2 DMS system, a systematic investigations have been undertaken. Samples were prepared by modified tartaric acid assisted sol-gel route and annealed in air between 300 to 600 ℃ in order to vary the crystallite sizes.. From Reitveld refinement of XRD data, FTIR, SAD patterns, Raman and XPS studies, it has been confirmed that the synthesized samples are having single phase tetragonal rutile structure. The tetragonality 'c/a' value seems to change systematically with decreasing crystallite size. TEM studies revealed that the surface nanoparticles are aggregating with increasing particle size without forming any secondary phases within the limit of surface diffusion of dopant. The reduction of intensities of Raman peaks, shift in their positions, their shape and size distribution are found to be influenced predominantly by the nano size of the materials. The optical band gap of the materials clearly indicates a blue shift with decreasing particle sizes. From XPS data, it has been observed that the core level Co 2p binding energy values and FWHM values have been changed systematically with decreasing the nano size of the materials. However, the non-linear variation of FWHM of Ols core level XPS spectra has been observed. These results are attributed not only due to the random distribution of crystallites and local structural disorder but also due to the effect of nano size on electronic structural modifications. Moreover, surface defects are playing main role in controlling the surface bonds and associated surface properties with varying crystallite size. The Magnetization studies clearly indicated the presence of room temperature ferromagnetism in all the prepared samples. Further, the mechanism was analyzed in influencing the nano size effects on the behaviour of ferromagnetism of nano crystalline Sn_(0.95)Co_(0.05)O_2 powders, which may exploit for spintronic, magneto-optical, magnetic storage and ferrofluidic applications.