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

Abstract

Magnetoelectric (Sr0.5Ba0.5Nb2O6)1􀀀x􀀀(CoFe2O4)x (x = 0.2–0.6) composites were prepared by a one-pot softchemistry synthesis using PEG400. Calcining at 700 ◦C resulted in nanocrystalline composite powders (dcryst. = 24–30 nm) which were sintered between 1050 and 1200 ◦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 μm for sintering up to 1150 ◦C, while sintering at 1200 ◦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 (αME) depends both on the CoFe2O4 fraction (x) and sintering temperature. The composite with x = 0.3 exhibits the largest αME value of 37 μV Oe􀀀1 cm􀀀1 (@ 900 Hz). With rising frequency of the AC driving field αME increases up to 300–400 Hz and is nearly constant until 1 kHz.