Preparation And Performance Of Magnetic - Electric Nano Composite Ceramics Research

Multifunctional nanopowders are required to prepare electric-magnetic element due to the device miniaturization. We prepared BaTiO3 and NiFe2O4 nanopowders and BaTiO3-NiFe2O4 nanocomposite powders with a hydrothermal menthod. And then, we researched the electric and magnetic properties of the ceramics sintered with these powders.Pure NiFe2O4 nanocrystal lines were synthesized with hydrothermal method under 0-7 mol/L alkali concentrations and different surfactants (PVP, SDS and DTAB). The crystal size of NiFe2O4 power increases firstly and then decreases with the alkali concentration. Relatively, the circular NiFe2O4 crystallites become square crystallites. The samples have high saturation magnetization relative to the crystal size and low coercivity. Then the NiFe2O4 nanopowders were sintered at different temperatures to obtain NiFe2O4 ceramics with different grain sizes. The NiFe2O4 ceramic properties were strongly dependent on the grain size. With the increase in the grain size, saturation magnetization (Ms) increased, magnetic permeability (μ) increased, Curie temperature (Tc) decreased, dielectric constant decreased and dielectric loss increased.We prepared BaTiO3 nanopowders with hydrothermal method, which were then pressed and sintered to BaTiO3 ceramics. The BaTiO3 dielectric constant increases slightly with the increase in alkali concentration, and then decreases from 1500 to 500 when the alkali concentration is 7 M. The double ferroelectric hysteresis loops were observed because the Na+ ions enter to the BaTiO3 lattices while hydrothermal reaction.Magnetoeletric nanocomposite powders of xNiFe2O4-(1-x)BaTiO3 (x=10,20,30, 40,50 mol%) were prepared with two steps by hydrothermal method based on the NiFe2O4 and BaTiO3 experiments. Nano core-shell structure with BaTiO3 shell and NiFe2O4 core were confirmed by XRD, Raman and HRTEM measurements. The perfect interfaces between magnetic and ferroelectric phases at lattice level were obtained. Saturation magnetization increases from 5 to 25 emu/g with the NiFe2O4 content increases from 10% to 50%. The composite ceramics were sintered from the nanocomposite powders. The grain size of the composite ceramics was still in naonsize without growth. With the increase in NiFe2O4 from 10% to 50%, saturation magnetization increases from 4.8 to 33 emu/g, magnetic permeability from 1.2 to 2.4 and dielectric constant decreases from 1156 to 174. The curves of magnetic permeability dependence on temperature appeared a weak peak, resulting from the dielectric peak of BaTiO3 at 460℃. These indicate a coupling between magnetic and dielectric phase due to the perfect lattice contact.Magnetoelectric composite with core-shell nanostructure provide a possible application in micro-electronic devices.