We investigate the effect of variable uniaxial tensile strain on the evolution of 71° ferroelastic domains in (001)-oriented epitaxial BiFeO3 (BFO) thin films using piezoresponse force microscopy (PFM). For this purpose, a newly designed bending stage has been employed, which allows tensile bending as wells as in situ PFM characterization. In situ PFM imaging reveals polarization-strain correlations at the nanoscale. Specifically, ferroelastic domains with in-plane polarization along the direction of applied tensile strain expand, whereas the adjoining domains with orthogonal in-plane polarization contract. The switching is mediated by significant domain wall roughening and opposite displacement of the successive walls. Further, the domains with long-range order are more susceptible to an applied external mechanical stimulus compared to the domains, which exhibit short-range periodicity. In addition, the imprint state of film reverses direction under applied tensile strain. Finally, the strain-induced changes in the domain structure and wall motion are fully reversible and revert to their as-grown state upon release of the applied stress. The strain-induced non-180° polarization rotation constitutes a route to control connected functionalities, such as magnetism, via coupled in-plane rotation of the magnetic plane in multiferroic BFO thin films.
Keywords: domain wall motion; ferroelastic switching; multiferroics; piezoresponse; polarization−strain correlation; uniaxial mechanical strain.