Structural, Optical, and Magnetic Properties of Nanocrystalline Co Doped SnO2 Based Diluted Magnetic Semiconductors

With the aim of understanding the structural, electronic, and magnetic properties of nanocrystalline Co doped SnO2 diluted magnetic semiconductors, prepared by the tartaric acid get route, a systematic investigation as a function of annealing temperature has been carried out. The precursor was characterized by TG-DTA to determine thermal decomposition and crystallization temperature. The XRD, TEM, FT-IR, and laser Raman studies revealed that all the samples have a tetragonal rutile structure with single phase. The average particle sizes obtained from TEM are in the range of 18-50 nm. The changes in Raman spectra were analyzed with varying crystallite size. The optical absorbance measurements revealed that the nanometric size of the materials influences the energy band gap values. From the XPS studies, the oxidation state of cobalt is found to be +2, and particle size induced implications in the core level XPS peaks of Co 2p and O 1s have been analyzed. The presence of room temperature ferromagnetism has been confirmed by the magnetization studies. Finally, it has been concluded that the ferromagnetic properties depend not only on the surface diffusion of Co ions and the distribution of defects such as oxygen vacancies or vacancy clusters but also on nanometric size of the materials and their surface conditions.