Fine-grained magnetoelectric Sr0.5Ba0.5Nb2O6-CoFe2O4 composites synthesized by a straightforward one-pot method

Magnetoelectric (Sr0.5Ba0.5Nb2O6)(1-x)-(CoFe2O4)(x) (x = 0.2-0.6) composites were prepared by a one-pot soft-chemistry synthesis using PEG400. Calcining at 700 degrees C resulted in nanocrystalline composite powders (d(cryst.) = 24-30 nm) which were sintered between 1050 and 1200 degrees C to ceramic bodies with relative densities up to 98%. SEM investigations confirm the formation of composite ceramics with a 0-3 connectivity and variable grain sizes from 0.2 to 3.6 mu m for sintering up to 1150 degrees C, while sintering at 1200 degrees C leads both to a change in the microstructure and a considerable grain growth. Magnetic measurements at 300 K reveal ferrimagnetic behaviour with saturation magnetization values smaller than bulk CoFe2O4 and coercivities between 790 and 160 Oe. Temperature-dependent impedance spectroscopy showed that the relative permittivities decrease both with rising frequency and CoFe2O4 fraction. The frequency dependence of the impedance can be well described using a single RC circuit. Magnetoelectric measurements show the presence of pronounced field hystereses. The maximum magnetoelectric coefficient (alpha(ME)) depends both on the CoFe2O4 fraction (x) and sintering temperature. The composite with x = 0.3 exhibits the largest alpha(ME) value of 37 mu V Oe(-1) cm(-1) (@ 900 Hz). With rising frequency of the AC driving field alpha(ME) increases up to 300-400 Hz and is nearly constant until 1 kHz.

Automated summary

Magnetoelectric composites were synthesized using PEG400 and characterized for their microstructure and magnetic properties. The composites exhibited ferrimagnetic behavior with variable saturation magnetization and coercivities. Impedance spectroscopy revealed a decrease in relative permittivities with increasing frequency and CoFe2O4 fraction. The magnetoelectric coefficient showed a dependence on both the CoFe2O4 fraction and sintering temperature, with a maximum value observed at x = 0.3. The frequency dependence of the coefficient was also investigated.