Engineering room-temperature multiferroicity in Bi and Fe codoped $BaTiO3$

Fe doping into BaTiO₃ stabilizes the paraelectric hexagonal phase in place of the ferroelectric tetragonal one. We show that simultaneous doping of Bi along with Fe into BaTiO₃ effectively enhances the magnetoelectric (ME) multiferroic response (both ferromagnetism and ferroelectricity) at room temperature, through careful tuning of Fe valency along with the controlled recovery of the ferroelectric-tetragonal phase. We also report a systematic increase in large dielectric constant values as well as reduction in loss tangent values with relatively moderate temperature variation of the dielectric constant around room temperature with increasing Bi doping content in $Ba1−xBixTi0.90Fe0.10O3$ (0 $≤$ x $≤$ 0.10), which makes the higher Bi–Fe codoped sample (x = 0.08) promising for use as a room-temperature high-κ dielectric material. Interestingly, the x = 0.08 (Bi–Fe codoped) sample is not only found to be ferroelectrically (∼20 times) and ferromagnetically (∼6 times) stronger than x = 0 (only Fe-doped) at room temperature, but also observed to be better insulating (larger bandgap) with indirect signatures of larger ME coupling as indicated from anomalous reduction of the magnetic coercive field with decreasing temperature. Thus, room-temperature ME multiferroicity has been engineered in Bi and Fe codoped BTO (BaTiO₃) compounds.