College Park, Maryland      June 6 - 10 , 2004

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TP62: Transport and magnetic properties of the perovskites Bi_1-xCa_xMn_0.95Cr_0.05O3 with x = 0.4, 0.5

C. C. Yang, F. C. Tsao, P. J. Hwang, W.-.H. Li (Department of Physics, National Central University, Chung-Li, 32054 Taiwan), J. W. Lynn (NIST Center for Neutron Research), J. R. Sun (State Key Laboratory of Magnetism, Institute of Physics and Center for Condensed Matter Physics, Chinese Academy of Sciences,Beijing 100080, China)

Polycrystalline samples of Bi_1-xCa_xMn_0.95Cr_0.05O₃ with x=0.4 and 0.5 were prepared by conventional ceramic route. Crystalline structures of the compounds were investigated by using the high-resolution neutron diffraction patterns and the Rietveld method. At room temperature, they crystallized into an orthorhombic Pbnm phase. Jahn-Teller distortion was found at around 280 K for the x =0.4 sample. Ac susceptibility reveals a charge ordered state in both samples, which occur at 280 and 285 K for the x = 0.4 and 0.5 samples, respectively. An applied magnetic field of strength 9 T can melt the charge ordered state. The transport behavior of both samples may be described by using the variable-range hoping mechanism. The magnetic structures for both compounds were studied by neutron magnetic diffraction measurements. The spins of both compounds become ordered below 90 K. Spin clusters were realized in both compounds, and phase separation was clearly revealed in the x=0.4 compound. Detailed magnetic structures will be discussed.

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