Spatially resolved mapping of ferroelectric switching behavior in self-assembled multiferroic nanostructures: Strain, size, and interface effects

Local ferroelectric polarization switching in multiferroic BiFeO ₃-CoFe₂O₄ nanostructures is studied using switching spectroscopy piezoresponse force microscopy (SS-PFM). Dynamic parameters such as the work of switching are found to vary gradually with distance from the heterostructure interfaces, while nucleation and coercive biases are uniform within the ferroelectric phase. We demonstrate that the electrostatic and elastic fields at interfaces do not affect switching and nucleation behavior. Rather, the observed evolution of switching properties is a geometric effect of the heterointerface on the signal generation volume in PFM. This implies that the heterostructures can be successfully used in devices, since interfaces do not act as preferential sites for switching. At the same time, small systematic variations of switching properties within the ferroelectric component can be ascribed to the long-range elastic and electrostatic fields in the heterostructure, which can be visualized in 2D.