Off-axis electron holography of manganite-based heterojunctions: Interface potential and charge distribution

The interfacial electrical potentials and charge distributions of two manganite-based heterojunctions, i.e., La_0.67Ca_0.33MnO₃/SrTiO₃:0.05 wt% Nb (LCMO/STON) and La_0.67Ca_0.33MnO₃/LaMnO₃/SrTiO₃:0.05 wt% Nb (simplified as LCMO/LMO/STON), are studied by means of off-axis electron holography in a transmission electron microscope. The influences of buffer layer on the microstructure and magnetic properties of the LCMO films are explored. The results show that when a buffer layer of LaMnO₃ is introduced, the tensile strain between the STON substrate and LCMO film reduces, misfit dislocation density decreases near the interfaces of the heterojunctions, and a positive magnetoresistance is observed. For the LCMO/STON junction, positive and negative charges accumulate near the interface between the substrate and the film. For the LCMO/LMO/STON junction, a complex charge distribution takes place across the interface, where notable negative charges accumulate. The difference between the charge distributions near the interface may shed light on the observed generation of positive magnetoresistance in the junction with a buffer layer.