Dielectric Behavior and Electro-Magnetic Coupling at Room Temperature in BiFeO3/PVDF and CoFe2O4/PVDF Composites

The dielectric properties of composites formed by dispersions of two types of ceramic particles, BiFeO3 (multiferroic) and CoFe2O4 (magnetic), in poly(vinylidene fluoride), PVDF, (which can present a ferroelectric phase) were studied at room temperature as a function of particle concentration. The characterization studies include determination of dielectric polarization curves in the presence of external magnetic fields, H (that is, P–E plots in the presence of H, where P is the dielectric polarization and E the external applied electric field). Impedance spectroscopy analysis shows the presence of several distributions of dipolar relaxation processes, some of which are assigned to charge rearrangements at the different interfaces of the system, for example at the ceramic-polymer interfaces. Negative magneto-electric coupling was observed at low ceramic proportion (where leakage currents are lower than 20 nA/cm2), that is, decrease of P when applying H, (∂P∂H)E<0. The negative coupling is opposite to prev...