Experimental investigation of optical and magneto optical effects of chemically synthesized cobalt nanocolloids

Surfactant coated (oleic acid) cobalt nanocolloids are synthesized using the chemical reduction technique. The colloidal cobalt particles are characterized by x-ray diffraction, transmission electron microscopy and a superconducting quantum interference device. Structural characterization of the samples confirms the formation of cobalt in fcc form. The magnetic field induced optical anisotropy is probed through Faraday rotation for both concentrated and diluted colloids. The magneto optical signals for different concentrations are analysed and it is observed that the behaviour can be fitted for a Langevin curve for diluted suspensions, while the deviation is higher for concentrated suspensions. Optical absorption spectra show quantum confinement of nanoparticles leading to a blue shift in the electronic energy band gap. The band gap varied from 2 eV to 4 eV showing semiconductor like behaviour. (paper)