Effects of the Bi3+ substitution on the structural, vibrational, and magnetic properties of bismuth layer-structured ferroelectrics

Bismuth layer-structured ferroelectric Bi3R2Ti3FeO15 (R=Bi, Nd, and Gd) ceramics were synthesized by conventional solid-state reaction. All the samples showed an orthorhombic structure with A2(1)am space group. Bi3Nd2Ti3FeO15 and Bi3Gd2Ti3FeO15 presented a reduction in the orthorhombicity when compared to Bi5Ti3FeO15. The magnetic susceptibility of all samples followed the Curie-Weiss law, with negative values of the Curie-Weiss temperature, demonstrating that the magnetic interactions are antiferromagnetic in nature. The magnetization curves suggested a weak canted antiferromagnetic behavior for temperatures below 25 K, followed by a linear behavior in the curves at high temperatures. Mossbauer spectroscopy measurements revealed an increase of the quadrupole splitting values as the temperature decreases, indicating that the samples present local distortions, favoring the existence of weak ferromagnetic phase via the antisymmetric Dzyaloshinskii-Moriya interaction.