Local temperature dependence study of bismuth ferrite upon 111In implantation: an atomic point of view for the In-site occupation

Multiferroic materials have gained a lot of attention in the past half century for their potential application in the technology industry, as they can be used in data storage, spintronics, and microelectronic devices.[1] This group of materials often show a low Néel and Curie temperature, usually below room temperature, leading to the loss of their multiferroic properties. That is why bismuth ferrite (BiFeO3 or BFO) has gained a lot of attention within multiferroic materials, as both of these temperatures are well above room temperature, and thus showing multiferroic properties that can be exploited for the development of technologies. This work presents the study of the temperature dependence of the nuclear quadrupole interactions in bismuth ferrite with time-differential γ − γ perturbed angular correlation (TDPAC) spectroscopy using 111In(111Cd) as a probe nuclei. The site assignment for the probe is discussed and it is most probable that the lattice location for the presented measurement conditions is the Fe-site. The x-ray powder diffraction (XRD) technique was employed to investigate the macroscopic crystal structure before and after the TDPAC experiments and thus investigate how the thermal treatment during the TDPAC measurements affected the sample. XRD provided with the amount of secondary phase present in the samples, and this varies according to the thermal treatment carried out. This work further presents the data taken below the Néel temperature. However, the fitting of combined hyperfine interactions is very complex and this analysis is foreseen as a future step. Moreover, a comparison was made using data obtained with the nuclear probe 111mCd(111Cd) to study the differences in the location of the probe within the BFO structure, as well as a comparison with other studies in which BFO is doped with indium. The results with BFO(111In) showed that a single electric field gradient was observed in all temperatures during the TDPAC experiments. The observable frequency associated with the α phase follows a parabolic trend with offset, throughout the values 128-98 [Mrad/s], with very small values of asymmetry parameter (η ≈ 0) and damping (δ ≈ 0). The change to the β phase was observed with the drop in the frequency values to ∼ 20 [Mrad/s], as well as with the increase of the asymmetry parameter towards 1 and the damping, reaching values of 10-12%. This indicates a first order transition. By comparing the obtained results with ab initio calculations of the electric field gradient and asymmetry parameter from the previous BFO(111Cd) research, which is possible because both probe atoms share intermediate state, it was possible to assign the 111In probe to the substitutional Fe-site.