Preparation of a BiFeO3/LaNiO3 multiferroic oxide superlattice structure by RF magnetron sputtering

Artificial superlattices consisting of multiferroic BiFeO₃ (BFO) and conductive LaNiO₃ (LNO) were grown epitaxially on a Nb-doped SrTiO₃ (STO) (001) single-crystal substrate at temperatures in a range 560–810 °C with a RF magnetron sputtering system. The superlattice contained 30 periods of symmetric BFO/LNO bilayers with a thickness of 2 nm of each individual layer. Ferroelectric and conductive superlattice materials of this type can serve for an investigation of the strain dependence of ferroelectric properties of BFO layers in superlattice structures.Measurements of X-ray reflectivity and X-ray diffraction at high resolution were employed to characterize the microstructure of these films. The formation of a superlattice structure was confirmed by the appearance of Bragg peaks separated by Kiessig fringes in the X-ray reflectivity curve and a diffraction pattern. The clearly discernible main feature and satellite features on both sides of the substrate feature about the (002) STO Bragg peak indicate the high quality of the BFO/LNO artificial superlattice structure formed on a STO substrate at all deposition temperatures.X-ray measurements show that these superlattice films become subject to greater compressive strain in the in-plane direction, and possess increased crystalline quality when increasing the deposition temperature to 660 °C. The measurement of hysteresis loops shows that the largest remanent polarization (P_r) occurs at 660 °C.