Spatially Inhomogeneous Metal-Insulator Transition in Doped Manganites

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Science  03 Sep 1999:
Vol. 285, Issue 5433, pp. 1540-1542
DOI: 10.1126/science.285.5433.1540

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Scanning tunneling spectroscopy was used to investigate single crystals and thin films of La1– xCaxMnO3(with x of about 0.3), which exhibit colossal magnetoresistance. The different spectroscopic signatures of the insulating (paramagnetic) and metallic (ferromagnetic) phases enable their spatial extent to be imaged down to a lateral scale of the order of 10 nanometers. Above the bulk transition temperatureT c, the images show mostly insulating behavior. Below T c, a phase separation is observed where inhomogeneous structures of metallic and more insulating areas coexist and are strongly field dependent in their size and structure. Insulating areas are found to persist far belowT c. These results suggest that the transition and the associated magnetoresistance behavior should be viewed as a percolation of metallic ferromagnetic domains.

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