Multiferroic behavior and impedance spectroscopy of bilayered BiFeO3/CoFe2O4 thin films

Lead-free bilayered multiferroic thin films consisting of BiFeO3(BFO) and CoFe2O4(CFO) layers with different thicknesses were grown on SrRuO3-coated Pt/TiO2/SiO2/Si substrates by radio frequency sputtering. The effects of constituent layer thicknesses on the ferroelectric and magnetic behavior have been studied. The physical behaviors are shown to strongly depend on the thicknesses of the constituent layers. BFO (220 nm)/CFO (30 nm) bilayered thin film demonstrated much improved ferroelectric and ferromagnetic behavior (2P(r)=144.2 mu C/cm(2), 2E(c)=778.0 kV/cm, M-s = 61.2 emu/cm(3), and H-c=200.8 Oe) as compared to those of the single layer BFO thin film. The dielectric behavior and conductivity of BFO (220 nm)/CFO (30 nm) bilayered thin film were investigated as a function of both temperature (in the range of 294-534 K) and frequency (in the range of 10(-1)-10(6) Hz), where an activation energy of similar to 1.11 eV for dielectric relaxation was demonstrated. From the conductivity behavior, an activation energies of similar to 0.98 eV was derived for dc conductivity are, implying that oxygen vacancies are involved in the conduction of the BFO (220 nm)/CFO(30 nm) bilayered film. (c) 2009 American Institute of Physics. [DOI: 10.1063/1.3153955]