Periodicity dependence of the ferroelectric properties in BiFeO₃/SrTiO₃ multiferroic superlattices

Artificial superlattices of (BiFeO₃)_m(SrTiO₃)_m (m=1–10 unit cells) consisting of multiferroic BiFeO₃ and insulating SrTiO₃ layers were fabricated on (100)-oriented SrTiO₃ substrates by pulsed laser ablation. The remnant polarization and leakage current behavior of these films were studied by varying the periodicity (8–80 Å) of the superlattice. Compared to single layer BiFeO₃ thin films, the leakage current was reduced by a few orders of magnitude on increasing the periodicity. Reduced leakage and intrinsic polarization hysteresis were observed and confirmed by pulsed polarization analysis for all periodicities (∼20–60 Å). The leakage current was dominated by space charge limited conduction.