Multiferroic behaviour and the magneto-dielectric effect in Bi5FeTi3O15 thin films

Thin films of Fe-containing the Aurivillius phase Bi5FeTi3O15 (BFTO) were successfully prepared by chemical solution deposition. The microstructure, ferroelectric behaviours, magnetic properties and the magneto-dielectric effect were investigated systematically at room temperature (RT). A definite hysteresis loop of the BFTO film was obtained with the remanent polarization (2Pr) ∼ 43.3 µC cm-2 under an electric field of 300 kV cm-1. To exclude the contribution of the leakage current to polarization, we studied the frequency dependence of hysteresis loops in the BFTO thin film and made positive-up-negative-down measurements. These results indicated the intrinsic ferroelectricity in the present BFTO film and it was supported by the ε-V curve. Furthermore, a weak ferromagnetism with an in-plane saturated magnetization (Ms) of ∼ 1.7 emu cm-3 was also observed in the BFTO film, which may have originated from the Fe2+-O-Fe3+ nanocluster and the F-centre exchange (FCE) mechanism. Therefore, the ferromagnetism could be considered as in nanoregions. More importantly, the magneto-dielectric effect was found with a magneto-dielectric coefficient of ∼-2.8% at a frequency of 100 kHz at RT. The probable origins of magnetic anisotropy and the magneto-dielectric effect were discussed. All these results demonstrated the RT multiferroic behaviour of the BFTO film.