Magnetoelectric Coupling in BaTiO3–CoFe2O4 Nanocomposites Studied by Impedance Spectroscopy Under Magnetic Field

BaTiO₃-CoFe₂O₄ nanocomposites with a 1/1 molar ratio were prepared by a combination of polyol synthesis (chimie douce) and a subsequent consolidation by spark plasma sintering. The nanocomposite samples, with a grain size about 50 nm showed a good mixing and a high density. Their impedance response was measured in the 5 Hz-1 MHz frequency range, under magnetic fields up to 1200 kA/m. Measurements were carried out in the 40-210 °C temperature range. We used the Jonscher´s universal relaxation law to analyze the electric conductivity results. Significant changes in the activation energies for long range conductivity and hopping conductivity were observed both at the coercive magnetic field of the ferrite and the Curie transition of the titanate. We show that the use of impedance spectroscopy, based on a wide frequency range, provides a far larger view of electric phenomena allowing a separation of the several contributions to the conductivity phenomena, as a function of the magnetic field.