  We have investigated the nanoscale switching properties of strain-engineered
BiFeO3 thin films deposited on LaAlO3 substrates using a combination of
scanning probe techniques. Polarized Raman spectral analysis indicate that the
nearly-tetragonal films have monoclinic (Cc) rather than P4mm tetragonal
symmetry. Through local switching-spectroscopy measurements and piezoresponse
force microscopy we provide clear evidence of ferroelectric switching of the
tetragonal phase but the polarization direction, and therefore its switching,
deviates strongly from the expected (001) tetragonal axis. We also demonstrate
a large and reversible, electrically-driven structural phase transition from
the tetragonal to the rhombohedral polymorph in this material which is
promising for a plethora of applications.
