Ferroic switching, avalanches, and the Larkin length: Needle domains in LaAlO3

Propagation of wedge-shaped needle domains in LaAlO3 is driven mechanically and the change of wall shapes is observed. Twin walls remain smooth, whereas the one-dimensional front line of the needle tip shows wiggles when propagating through defect fields. The front line becomes highly distorted during approach to, or retraction from, the sample surface. Singularities of the characteristic (similar to Larkin) length occur when the front line breaks. Elastic forces produce planar twin walls with very large Larkin lengths, whereas the front line is not restrained by the compatibility energy and displays considerably shorter Larkin lengths. (C) 2011 American Institute of Physics. [doi:10.1063/1.3650475]