Influence of ex-situ thermal treatment on the chemical states, microstructure and ferroelectrics properties of polycrystalline BiMnO3-δ thin films

Abstract

Nanoelectronic devices based on oxide films require materials that may exhibit combined properties such as ferroelectricity, ferromagnetism, and/or ferroelasticity at the same phase. In this sense, multiferroic perovskite BiMnO3-δ thin films exhibit a relevant combination of ferroelectricity and ferromagnetism suitable for device applications. The purpose of this work is to investigate the growth conditions of BiMnO3 thin films using radio-frequency magnetron sputtering and the role of ex-situ thermal treatments under different conditions, which resulted in a P21/c to C2 phase transformation and BiMnO2.93 composition. The crystal structure of the BiMnO3-δ thin films was investigated using X-ray diffraction, high-resolution transmission electron microscopy, ultraviolet-visible spectrophotometer, X-ray photoelectron spectroscopy, and resistivity measurement, to correlate structural and transport properties. The ex-situ thermal treatment was performed in a bismuth and oxygen atmosphere in order to compensate for Bi and O deficiencies. Thus, the result was not an ideal stoichiometric, BiMnO3-δ proved to enhance the ferroelectric properties and other physical properties. The optimized thin films exhibit ferromagnetism up to 37 K, while ferroelectricity remains up to room temperature.