| Summary: | 碩士 === 國立東華大學 === 應用物理研究所 === 92 ===
We report the investigations of x-ray diffraction, resistivity, and magnetization on the colossal magnetoresistance (CMR) perovskite samples of La0.7Sr0.3(Mn1-xRux)O3 with x = 0 to 1.0. It is found that the undergoes pronounced peaks due to the ferromagnetic-paramagnetic phase transition in these compounds. However, the metal to insulator transition temperatures TP determined from the resistivity is consistently lower than that of the Curie temperature TC determined from the magnetization measurements. By replacing Mn with Ru, both TC and TP concurrently decrease and the studied materials are driven toward to the insulating phase with larger x. These observed results imply that the dopant of Ru has the effect of breaking the domain Mn3+-O-Mn4+ double exchange and weakening the ferromagnetism and metallicity to the La0.7Sr0.3MnO3 perovskite. The decrease in TC at a doping level of x = 0.10 is only ~10K which is considerably smaller than the one observed for doping with other elements such as Fe (ΔTC = ~100K). The observations indicate that an exchange coupling interaction like a new double exchange between Ru4+ and Mn3+ has existed. This interaction is positive in nature because, by virtue of Ru being a 4d metal, it has itinerant 4d electrons and extend 4d orbital. This facilitates a strong hybridization between Ru: 4d-O:2p orbital and enhances the exchange coupling with the Mn.
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