Temperature dependence of the local electromagnetic field at the Fe site in multiferroic bismuth ferrite

In this paper, we present a study of the temperature-dependent characteristics of electromagnetic fields at the atomic scale in multiferroic bismuth ferrite (BiFeO$_3$ or BFO). The study was performed using time differential perturbed angular correlation (TDPAC) spectroscopy on implanted 111In (111Cd) probes over a wide temperature range. The TDPAC spectra show that substitutional $^{111}$In on the Fe$^{3+}$ site experiences local electric polarization, which is otherwise expected to essentially stem from the Bi$^{3+}$ lone pair electrons. Moreover, the TDPAC spectra show combined electric and magnetic interactions below the Néel temperature $T_N$. This is consistent with simulated spectra. X-ray diffraction (XRD) was employed to investigate how high-temperature TDPAC measurements influence the macroscopic structure and secondary phases. With the support of ab initio DFT simulations, we can discuss the probe nucleus site assignment and can conclude that the $^{111}$In ($^{111}$Cd) probe substitutes the Fe atom at the B site of the perovskite structure.