Woo Seok Choi, Ji-Hwan Kwon, Hyoungjeen Jeen, Jorge E. Hamann-Borrero, Abdullah Radi, Sebastian Macke, Ronny Sutarto, Feizhou He, George A. Sawatzky, Vladimir Hinkov, Miyoung Kim, Ho Nyung Lee
Epitaxial strain imposed in complex oxide thin films by heteroepitaxy is recognized as a powerful tool for identifying new properties and exploring the vast potential of materials performance. A particular example is LaCoO3, a zero spin, nonmagnetic material in the bulk, whose strong ferromagnetism in a thin film remains enigmatic despite a decade of intense research. Here, we use scanning transmission electron microscopy complemented by X-ray and optical spectroscopy to study LaCoO3 epitaxial thin films under different strain states. We observed an unconventional strain relaxation behavior resulting in stripe-like, lattice modulated patterns, which did not involve uncontrolled misfit dislocations or other defects. The modulation entails the formation of ferromagnetically ordered sheets comprising intermediate or high spin Co3+, thus offering an unambiguous description for the exotic magnetism found in epitaxially strained LaCoO3 films. This observation provides a novel route to tailoring the electronic and magnetic properties of functional oxide heterostructures.
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http://arxiv.org/abs/1208.3479
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