Ferroelectric and mutiferroic materials have been studied from the viewpoint of pure
and applied physics. For the applications, a study from the viewpoint of materials science
will be important in the future. Examples of materials science study are substitution of
elements, selection of substrate in thin films and in-situ observation. Nano-scale domain
configurations of multiferroic BiFeO3 thin films and their dynamic response to the
externally applied fields have been investigated by piezoresponse force microscopy.
High-resolution piezoresponse images reveal that nano-scale domain walls are
approximately with ~2 nm in width. In this article, we focus on BiFeO3 as mutiferroic
materials and as ferroelectric materials. We will present our results about electric and
magnetic properties, and scanning probe microscopy observations. Local polarization
reversal and retention behavior will also be presented and discussed.