  Fe doping into BaTiO3, stabilizes the paraelectric hexagonal phase in place
of the ferroelectric tetragonal one [P. Pal et al. Phys. Rev. B, 101, 064409
(2020)]. 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
ferroelectric-tetragonal phase. We also report systematic increase in large
dielectric constant values as well as reduction in loss tangent values with
relatively moderate temperature variation of dielectric constant around
room-temperature with increasing Bi doping content in Ba1-xBixTi0.9Fe0.1O3
(0<x<0.1), which makes the higher Bi-Fe codoped sample (x=0.08) promising for
the use as room-temperature high-k dielectric material. Interestingly, 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 magnetic coercive field with decreasing temperature. Thus, room-temperature
ME multiferroicity has been engineered in Bi and Fe codoped BTO (BaTiO3)
compounds.
