Improved multiferroic properties of Nb doped BiFeO3

Abstract

Pure BiFeO3 (TN = 370 °C and TC = 826–845 °C) exhibits poor ferroelectric (high electrical conductivity) and weak ferromagnetism. In this study, up to 1% Nb5+ was introduced to replace Fe3+ (B-site doping) since it could disturb the nearly antiparallel spin ordering of the adjacent Fe3+ ions responsible for cycloidal (spiral) spin structure. On the other hand, the pentivalent Nb cations will compensate the negatively charged defects and consequently reduce the electrical conductivity. Unlike pure BiFeO3, the sample with 1% Nb exhibits hard magnetic behaviour due to its high coercive magnetic field of ~7460 Oe (at H = 50 000 Oe). The ferroelectric response for the sample with 0.2 % Nb was unstable above 40 kV/cm, while at 70 kV/cm only the sample with 1 % Nb showed a regular ferroelectric response with remnant electrical polarization of 0.5 μC/cm2 and coercive electrical field of 22.2 kV/cm. Thus, by doping with Nb, both magnetic and ferroelectric properties of BiFeO3 were improved.