  First-principals calculations show that up-spin and down-spin carriers are
accumulating adjacent to opposite surfaces of BiFeO3(BFO) film with applying
external bias. The spin carriers are equal in magnitude and opposite in
direction, and down-spin carriers move to the direction opposing the external
electric field while up-spin ones along the field direction. This novel spin
transfer properties make BFO film an intriguing candidate for application in
spin capacitor and BFO-based multiferroic field-effect device.
