Orientation-adjusted anomalous insulator-metal transition in NdNiO3/LaMnO3 bilayers

NdNiO3/LaMnO3 (NNO/LMO) bilayers were epitaxially grown on SrTiO3 (STO) substrates with different orientations by the polymer-assisted deposition technique. A well crystallization quality of the bilayers is confirmed by X-ray diffraction. Two consecutive transitions, an anomalous insulator-metal transition at ∼100 K followed by the typical metal-insulator transition at ∼171 K, are observed in the (001)-oriented NNO/LMO/STO bilayer. The anomalous insulator-metal transition temperature increases to 142 K for the (111)-oriented NNO/LMO/STO bilayer. Meanwhile, the magnetic properties of the NNO/LMO bilayers show an obvious difference with [100] and [111] orientations. Considering the different strain directions and the related oxygen octahedral distortion/rotation, it is suggested that the magnetic changes and the low-temperature anomalous insulator-metal transition in the NNO/LMO bilayers are attributed to the strong interlayer exchange coupling and charge transfer adjusted by the substrate orientation, whic...