Misfit dislocations of anisotropic magnetoresistant Nd_(0.45)Sr_(0.55)MnO_3 thin films grown on SrTiO_3 (110) substrates

摘要

Nd_(0.45)Sr_(0.55)MnO_3 is an A-type antiferromagnetic manganite showing obvious angular-dependent magnetoresistance, which can be tuned by misfit strain. The misfit strain relaxation of Nd_(0.45)Sr_(0.55)MnO_3 thin films is of both fundamental and technical importance. In this paper, microstructures of epitaxial Nd_(0.45)Sr_(0.55)MnO_3 thin films grown on SrTiO_3 (110) substrates by pulsed laser deposition were investigated by means of (scanning) transmission electron microscopy. The Nd_(0.45)Sr_(0.55)MnO_3 thin films exhibit a two-layered structure: a continuous perovskite layer epitaxial grown on the substrate followed by epitaxially grown columnar nanostructures. An approximately periodic array of misfit dislocations is found along the interface with line directions of both (111) and [001]. High-resolution (scanning) transmission electron microscopy reveals that all the misfit dislocations possess a-type Burgers vectors. A formation mechanism based on gliding or climbing of the dislocations is proposed to elucidate this novel misfit dislocation configuration. These misfit dislocations have complex effects on the strain relaxation and microstructure of the films, and thus their influence needs further consideration for heteroepitaxial perovskite thin film systems, especially for films grown on substrates with low-symmetry surfaces such as SrTiO_3 (110) and (111), which are attracting attention for their potentially new functions.