Anomalous Magnetoelectric Coupling Effect of CoFe2O4–BaTiO3 Binary Mixed Fluids

We report an anomalous magnetoelectric coupling effect of CoFe2O4–BaTiO3 binary mixed fluids, which were prepared by distributing surfactant treated (oleic acid) magnetic CoFe2O4 and ferroelectric BaTiO3 nanoparticles into highly insulating base fluid (silicone oil). A strong coupling effect in this mixed fluid has been observed, in which both the remnant polarization/magnetization and coercive electric/magnetic field are found to be enhanced visibly in the presence of an external magnetic/electric field. Colossal converse and direct magnetoelectric coupling coefficients are estimated to be α H = 1.22 × 10–4Oe·cm/V and α E = 2.52 × 104 V/(cm·Oe), respectively. Moreover, this coefficient clearly depends on the volume fraction of the two kinds of particles and the applied external magnetic/electric field. Even more amazing, CoFe2O4 also shows a strong magnetoelectric coupling effect with a coefficient as high as 4.2 × 10–5 Oe·cm/V. Further analysis indicates that the aggregated, chain-like structure of the particles under the action of external fields is believed to be responsible for the clamping effect, which in turn induces the observable anomalous coefficient. The field generated chain-like structure shows intense relaxation behavior with a relaxation time of several minutes. These results provide valuable information for enhancing the coupling effect of mixed fluids and may be important for practical applications in magnetoelectric devices.