Artificial superlattice structures consisting of alternating epitaxial layers of materials with dissimilar physical properties offer exciting new possibilities both in the investigation of fundamental physical phenomena and in the exploitation of novel properties for diverse applications. In this work, symmetric epitaxial superlattice structures of multiferroic BiFeO₃ (BFO) and conductive LaNiO₃ (LNO) sublayers were grown on a Nb-doped SrTiO₃ substrate with rf magnetron sputtering at temperature 660 ^oC. The superlattices contained 6 – 30 periods of BFO/LNO bilayers with a sublayer thickness in a range 1.7 – 8.5 nm; the total thickness of the films was fixed at ~ 100 nm. We characterized the structure of the interface and the surface morphology of these films by measuring X-ray reflectivity (XRR) and diffraction. The formation of a superlattice structure was confirmed from the appearance of satellite features on both sides of the main feature in the X-ray diffraction (XRD) pattern. The periods and thickness of the superlattice confirmed by XRD and XRR are consistent with the results of secondary-ion mass spectrometer (SIMS). X-ray measurements show that these superlattice films become subject to greater tensile stress along the c-axis and increased compressive stress parallel to the surface plane with decreasing thickness of the sublayer. The BFO sulayer in the artificial superlattice is under biaxial compressive stress whereas the LNO sublayer is under biaxial tensile stress. The smaller is the thickness of the sublayer, the greater is the crystalline quality and the strain state. The hysteresis loops show a large leakage current at frequencies 0.5 and 1 kHz; the polarization decreases with increasing frequency. An intrinsic remanent polarization of the superlattices was observed at the thickness of a sublayer in the range 1.7 – 8.5 nm at 5 kHz. The rounded shape of the hysteresis loop at frequency ≤ 2 kHz resulted from large dc leakage and extrinsic interface effects.

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1. Structural characteristics of BiFeO₃/LaNiO₃ artificial superlattices prepared by rf magnetron sputtering