Charge Transfer, Orbital Reconstruction, and Induced Magnetic Coupling in Manganite/BiFeO3 Heterostructures

La0.7Sr0.3MnO3/BiFeO3 (LSMO/BFO) and LaMnO3/BiFeO3 (LMO/BFO) heterostructures were prepared on (001)-oriented SrTiO3 (STO) substrates by pulsed-laser deposition, and the magnetic exchange coupling and the charge transfer procedure at the heterointerfaces were investigated. The LSMO/BFO and LMO/BFO heterostructures exhibited an exchange bias with a magnetic field H-EB = 46 Oe and HEB = 30 Oe, respectively. The charge transfer procedure is determined from Fe ions to Mn ions at the LSMO/BFO interface, conversely from Mn ions to Fe ions at the LMO/BFO interface. The charge transfer from Fe ions to Mn ions can lead to stronger interfacial magnetic coupling. According to the charge transfer mode, we describe possible microscopic scenarios of orbital reconstruction at the LSMO/BFO and LMO/BFO interfaces. Our work sheds light on the origin of the exchange bias effect in the manganite/BFO heterostructures.