Magnetoelectric features in the magnetic hysteresis of modified multiferroic BiFeO3: Release of latent magnetization induced by cationic modification

Abstract

BiFeO3 is a well-known room temperature multiferroic material. However, the presence of antiferromagnetic magnetic order and high leakage current limit its utilization in magnetoelectric devices. This study deals with conclusive identification of the presence of magnetoelectric coupling by carefully selecting higher bond strength cationic substitution and using contactless measurement. Complementary to the magnetic studies, detailed structural analyses are carried out to determine the B-site bond length, B-site bond angle, ionic size mismatch and electronic structure of the substituent. The structural modification due to cationic substitution leads to release of latent magnetization that is locked within the cycloid. Non-monotonic temperature dependence of magnetic coercivity is observed and the results are confirmed for various compositions. These results are explained using Ginzburg-Landau Mean field model. Crossover from anomalous to usual trend of magnetic coercivity as a function of temperature is presented covering the temperature regime beyond Neel temperature of BiFeO3. Results are explained in terms of effective anisotropy which includes contribution associated with the electric polarization. This proves the existence of magnetoelectric effect. Magnetic switching is shown to be affected by the presence of ferroelectric order. The inclusion of normal ferromagnetic response in the high temperature regime makes this a unique study. The importance of this study lies in the fact that such magnetoelectric characteristic cannot be explored through the conventional electrical response measurements as the presence of high leakage current in BFO makes such measurements extremely difficult.