Structure refinement of (La1-XNdX)0.7Sr0.3MnO3 system by Rietveld method and the relationship to magnetic properties

• Main Authors: Bing-Yuan Chen, 陳炳元
• Other Authors: Tsong-Jen Lee
• Format: Others
• Language: zh-TW
• Published: 1999
• Online Access: http://ndltd.ncl.edu.tw/handle/04523184790509152669

碩士 === 國立清華大學 === 物理學系 === 87 === A series of samples with nominal compositions of (La1-XNdX)0.7Sr0.3MnO3 (X = 0, 0.25, 0.5, 0.75, 1) system were prepared by solid state reaction process. The observation of "colossal" magnetoresistance (CMR) in these perovskite structural compounds has generated considerable interest in the physical properties of this class of compounds, particularly the interplay of structure, magnetism and electronic transport. It is believed that the CMR effect is due to a double exchange of electrons between ferromagnetically coupled Mn+3 and Mn+4 ions. Based on this reason, we have examined a series of samples, (La1-XNdX)0.7Sr0.3MnO3, Mn+3/Mn+4 ratio is fixed at 7/3. Powder X-ray diffraction method and Rietveld refinements were used to accomplish the structural analyses of these samples. With increasing X content, the structural symmetry changes from trigonal phase of (hexagonal axes, no.167) for X = 0, 0.25 to orthorhombic phase of Pnma (No.62) for X = 0.5, 0.75, 1. The lattice parameters a, b, c and angle of Mn-O-Mn are decreasing as X is increasing form 0 to 1. Magnetization and resistivity measurments indicate that the ferromagnetic-paramagnetic temperature Tc for these samples are almost the same as the metal-insulator temperature Tp and the largest magnetoresistance for each sample appeared around the temperature Tp. In addition, we observe that temperature Tc and Tp are decreasing as the Nd's content X is increasing.