  The switching dynamics of a single-domain BiFeO3/CoFe heterojunction is
modeled and key parameters such as interface exchange coupling coefficient are
extracted from experimental results. The lower limit of the magnetic order
response time of CoFe in the BiFeO3/CoFe heterojunction is theoretically
quantified to be on to the order of 100 ps. Our results indicate that the
switching behavior of CoFe in the BiFeO3/CoFe heterojunction is dominated by
the rotation of the Neel vector in BiFeO3 rather than the unidirectional
exchange bias at the interface. We also quantify the magnitude of the interface
exchange coupling coefficient J_int to be 0.32 pJ/m by comparing our simulation
results with the giant magnetoresistance (GMR) curves and the magnetic
hysteresis loop in the experiments. To the best of our knowledge, this is the
first time that J_int is extracted quantitatively from experiments.
Furthermore, we demonstrate that the switching success rate and the thermal
stability of the BiFeO3/CoFe heterojunction can be improved by reducing the
thickness of CoFe and increasing the length to width aspect ratio of the
BiFeO3/CoFe heterojunction. Our theoretical model provides a comprehensive
framework to study the magnetoelectric properties and the manipulation of the
magnetic order of CoFe in the BiFeO3/CoFe heterojunction.
