Large negative magnetoelectric coupling in Fe substituted ferroelectric Bi_0.5Na_0.5TiO₃: An experimental study supported by Landau-Devonshire free-energy model based calculations

This work presents an experimental and analytical study of a negative magnetoelectric (ME) effect observed in Fe substituted Bi_0.5Na_0.5TiO₃ (BNT). Experiments are performed on solid solutions of Bi_0.5Na_0.5(Fe_xTi_{(1 − 3x/4)})O₃ (BNFT), for x = 0 to 0.2, synthesized using the conventional solid state reaction route. X-ray diffraction studies confirm that Fe ions are completely soluble in a BNT matrix, up to the highest solubility of x = 0.2, thus forming a single-phase perovskite structure. As expected, partial substitution of Fe ions at Ti⁴⁺ sites diminishes the ferroelectric behavior of BNFT. For the optimal composition of x = 0.05, electrical poling of the sample results in an ∼19% decrease in magnetization, i.e., a large negative ME coupling is observed. Experimental results are supported by the Landau–Devonshire thermodynamic model based calculations for single-phase multiferroics. The model is utilized to obtain a theoretical estimate of the ME coupling coefficient of approximately −430 kV/cm Oe.