Magnetodielectric effect in Co3O4 nanoparticles grown within a silica glass

Co₃O₄ nanocrystals of sizes in the range 17.5-33.1 nm were grown within a sol-gel-derived silica glass matrix. Rietveld analysis of the X-ray diffraction data showed that the crystals had tetragonal symmetry. This was explained as arising due to a tensile strain induced at the glass-crystal interface as a result of thermal expansion mismatch between the phases. The crystals showed ferromagnetic behaviour with superparamagnetism setting-in at temperatures above 15 K. They also exhibited ferroelectric characteristics with large remanent polarization. Change in dielectric constant as a function of magnetic field was observed in these nanocomposites. This was discussed on the basis of magnetostriction effect.