Optimal growth windows of multiferroic BiFeO3 films and characteristics of ferroelectric domain structures

Multiferroic BiFeO3 films of smooth surface and fully-saturated ferroelectric hysteresis loops have been grown by RF magnetron sputtering. The (001)-oriented epitaxial films showed a large remanent polarisation of 61 mu C/cm(2). A strategy to grow BiFeO3 films of good ferroelectric property was demonstrated, that was using fast growth rate to achieve accurate stoichiometry for the BiFeO3 phase and at the same time to avoid the formation of impurity phases associated with the fast growth by accurate control of thermodynamic parameters such as oxygen partial pressure and temperature, as well as proper selection of substrates. Piezoresponse force microscopy revealed fine spontaneous domains for highly resistive epitaxial films, which were switchable under DC biases. For the polycrystalline films of increased density of free carriers, single-domain grains of about 200 nm in diameter were observed due to effective compensation of depolarisation field by free carriers and therefore allowing larger domains. (C) 2009 Elsevier B.V. All rights reserved.