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Direct Imaging of Nanoscale Phase Separation in La0.55Ca0.45MnO3: Relationship to Colossal Magnetoresistance

J. Tao,1,2* D. Niebieskikwiat,3,4 M. Varela,1 W. Luo,1,5 M. Schofield,2 Y. Zhu,2 M. B. Salamon,3,6 J. M. Zuo7,8 S. T. Pantelides,5,1 S. J. Pennycook1,5

Phys. Rev. Lett. 103, 097202 (2009)

A nanoscale phase is known to coincide with colossal magnetoresistance (CMR) in manganites, but its volume fraction is believed to be too small to account for CMR. Scanning-electron-nanodiffraction images show nanoclusters as they form and evolve with temperature in La1-xCaxMnO3, with x = 0.45. They are not doping inhomogeneities and their structure is that of the bulk compound at x = 0.60, which at low temperatures is insulating. Their volume fraction peaks at the CMR critical temperature and is estimated to be 22% at finite magnetic fields. In view of the known dependence of the nanoscale phase on magnetic fields, such a volume fraction can account for the CMR peak.

Intensity maps of the superlattice reflections in La0.55Ca0.45MnO3 as the temperature is raised through the ferromagnetic - paramagnetic phase transition. A color scale of relative intensity is shown on the right. The flat blue area has the intensity of superlattice reflections below the noise level. Each map is from an area of 12 × 12 nm2 with the scanning step of 1 nm.

1Materials Science & Technology Division, Oak Ridge National Laboratory
2Condensed Matter Physics & Materials Science Department, Brookhaven National Laboratory
3Department of Physics, University of Illinois at Urbana-Champaign
4Colegio de Ciencias e Ingeniería, Universidad San Francisco de Quito, Ecuador


 Oak Ridge National Laboratory