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Use of the photoacoustic spectroscopy for surface characterization of nanometer-sized cobalt-ferrite particles

Photoacoustic spectroscopy was used in the investigation of cobalt ferrite nanosized particles (about 5 nm in diameter) surface-uncoated or surface-coated with different species. The surface-coated nanoparticles display well defined photoacoustic features in the wavelength region typical of d-d transitions of the transition element ions. Removal of the surface-coating layer by thermal treatment strongly quenches the photoacoustic feature, probably due to the randomization of the surface metal-ion site symmetry.