Magnetodielectric study in SiO₂-coated Fe₃O ₄ nanoparticle compacts

The dielectric properties of Fe₃ O₄ magnetic nanoparticles with an insulating coating layer of SiO₂ were investigated. At high temperatures, the changes in the dielectric constant and loss induced by the magnetic field are opposite in sign and strongly frequency-dependent, which originates from extrinsic magnetodielectric coupling-the Maxwell-Wagner effect combined with magnetoresistance. And the interface defects leads to the obvious hysteresis phenomena observed in the measurements. On the other hand, the strong coupling of dielectric and magnetic properties at low temperatures contradicts the Maxwell-Wagner model, suggesting the intrinsic magnetodielectric coupling. Our observations are consistent with the recent polarization switching measurements, which confirm the low-temperature multiferroic state existing in highly lossy Fe₃ O₄. And the core/shell nanostructure may provide a new route to achieve applicable magnetoelectric materials with low loss.