Control of the nanostructure in percolative multiferroic composites on the dielectric loss and magnetism threshold

Revealing clearly the control of the microstructure on the dielectric and magnetic properties of multiferroic composites is of great importance in designing a composite with high performance. In this paper, BTO/NZFO composite thin films with solid solution constituent phases around 20 nm were prepared by RF magnetron sputtering. The lattice constant, grain size, intrinsic and extrinsic oxygen vacancies and non-stoichiometric defects in the nanocomposite thin film are measured by XRD, TEM and XPS. The conductivity, dielectric properties and magnetic performances of the nanocomposite are measured by an impedance analyzer and MPMS respectively. In this multisusceptible nanocomposite thin film, the permittivity is compatible with the Kirkpatrick model, and the dielectric loss is controlled importantly by the high fraction of grain boundaries which restrains the charge migration and thus makes the loss significantly low. The saturation magnetization of the nanocomposite thin film is influenced mainly by the lattice deformation of the nanosized constituent phases. The magnetic threshold of the nanocomposite shifts downwards from the real topological one, which is profitable for the composite to contribute simultaneously a low dielectric loss and high permeability. The coercivity, which is controlled by the grain size of NZFO and magnetic communication among NZFO nanoparticles, displays a novel percolation behavior.