College Park, Maryland      June 6 - 10 , 2004

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TP11: Neutron Diffraction Study of Magnetic, Structural, and Charge Ordering in La_0.48Ca_0.52MnO₃ and La_0.52Ca_0.48MnO₃

E. Rodriguez, T. Proffen, A. Llobet, J.J. Rhyne (Los Alamos Neutron Science Center, Los Alamos National Laboratory)

Mixed valence manganites show an enormously rich range of magnetic, structural, and transport properties with varying stoichiometric composition and temperature. Neutron powder diffraction studies were done on the perovskite manganite La_1-xCa_xMnO₃ series for compositions x = 0.48 and x = 0.52. The interplay between the magnetic, charge, and structural ordering forms a complex system due to an ad mixture of Mn⁴⁺ and Mn³⁺ ions in these compositions. These two compositions alone exhibit interesting physical properties such as coexisting ferromagnetic and anti-ferromagnetic phases at the same temperature. Studies have shown the x = 0.5 composition to be the metal-insulator transition (MIT) interface for this manganite series. Therefore, phase separation at lower temperatures and the magnetic transition temperatures are important characteristics examined in this analysis. The neutron powder measurements were done on two spallation-source diffractometers located at the Manuel Lujan Jr. Neutron Scattering Center at Los Alamos National Laboratory. In addition to crystallographic and magnetic structure analysis, a pair-distribution function (PDF) study was done as well. A PDF analysis provides short-range order information of manganites such as the distortion of its perovskite structure due to the Jahn-Teller effect. This study hopes to understand the magnetic, structural, and transport properties of these manganites for compositions close to and on opposite sides of the MIT boundary.

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