Modelling of twinning in epitaxial (001)-oriented La0.67Sr0.33MnO3 thin films
N. Farag, M. Bobeth, W. Pompe, A. E. Romanov, J. S. Speck
Journal Applied Physics 97, 113516 (2005)
Twinning, i.e. the formation of structural domains, in La1-xSrxMnO3 thin films, which grow coherently on (001)-oriented cubic substrates, is explained as a result of shear strain relaxation within the distorted rhombohedral La1-xSrxMnO3 crystal lattice. A one-dimensional periodic model structure of twins is proposed and the non-uniform elastic strains within twinned La1-xSrxMnO3 films are calculated by applying the coherency defect technique. The strain field depends on the ratio of domain width and film thickness and exhibits maxima at the triple junctions of the domain boundaries and the film/substrate interface. The equilibrium domain width is derived as a function of the film thickness by minimizing the total energy of the system including contributions from elastic strain and domain wall energy. From comparison of the theoretical results with recent electron microscope observations of twins the domain wall energy can be predicted. From the observed average domain width in La0.67Sr0.33MnO3 films, the domain wall energy of 1.35 mJ/m2 is suggested. The possibility of a preferred nucleation of the ferromagnetic phase at triple junctions due to spatial strain variations is discussed.