Thickness-dependent 109° domain evolution in multiferroic BiFeO3 thin films

Ferroelectric and ferroelastic 109 degrees domain structure has great potentialities in ferroelectric and magnetoelectric devices. Understanding their structure is crucial to control the domain configurations for potential applications. In this work, a series of BiFeO3 (BFO) thin films with various thicknesses are investigated by piezoelectric force microscopy and transmission electron microscopy. Contrast analysis and electron diffractions reveal that the BFO films are mainly composed of 109 degrees domains with small populations of charge domain walls and vortex structures. The domains are observed to be distributed periodically, and the sizes fall outside the validity range of the square root law, while gamma = 0.9 scaling exponent is revealed. These differences are discussed on the basis of ways of reducing the depolarization field energy by the coexistence of charge domain walls and vortex structures as well as bound charges near the surface. (C) 2019 The Japan Society of Applied Physics