Dielectric properties of magnetic-ferroelectric CoO–NaNO$_{2}$–porous glass nanocomposite

Dielectric properties of the nanostructured multiferroic composite on the basis of silicate porous glass simultaneously filled with ferromagnetic (cobalt oxide CoO) and ferroelectric (sodium nitrite) materials have been investigated in wide temperature (270–570 K) and frequency (10$^{-1}$–10$^{7}$ Hz) ranges. The mean diameter of pores in the matrix is 7 $\pm$ 1 nm. The magnetic material particles are synthesized directly in the pores of the glass matrix and occupy about 10% of the pore volume. The porous glass is well wetted with NaNO$_{2}$. The latter easily infiltrates into the glass and occupies 90% of the remaining unfilled pore volume. The dielectric response of matrices filled with both the components together and with each component separately is studied. An analysis of the obtained data makes it possible to reveal the contributions of individual components into the dielectric response of the composite and the influence of the confined geometry on their dielectric properties. It is found that the incorporation of CoO nanoparticles leads to an order of magnitude increase in the dielectric permittivity and electrical conductivity of the two-component composite in comparison with these values for the composite filled solely with sodium nitrite and to a decrease in the activation energy over the entire studied temperature range. These studies are of interest not only as a preliminary investigation prior to the study of the effect of a magnetic field on the dielectric properties of the synthesized composite, but are of independent physical interest as well, since they allow one to determine the influence of the confined geometry on the dielectric properties of magnetic metal oxides and on the of their phase transition parameters.