Local dielectric measurements of BaTiO₃–CoFe₂O₄ nanocomposites through microwave microscopy

We report on linear and nonlinear dielectric property measurements of BaTiO₃–CoFe₂O₄ (BTO–CFO) ferroelectromagnetic nanocomposites and pure BaTiO₃ and CoFe₂O₄ samples with scanning near-field microwave microscopy. The permitivity scanning image with spatial resolution on the micrometer scale shows that the nanocomposites have a very uniform quality with an effective dielectric constant ɛ_r = 140 ± 6.4 at 3.8 GHz and room temperature. The temperature dependence of dielectric permittivity shows that the Curie temperature of pure BTO was shifted by the clamping effect of the MgO substrate, whereas the Curie temperature shift of the BTO ferroelectric phase in BTO–CFO composites is less pronounced, and if it exists at all, would be mainly caused by the CFO. Nonlinear dielectric measurements of BTO–CFO show good ferroelectric properties from the BTO.