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首页> 美国政府科技报告 >Effects of dynamic Jahn-Teller distortions by Raman spectroscopy in the layered CMR manganite La(sub 2(minus)2x)Sr(sub 1+2x)Mn(sub 2)O(sub 7), x = 0.36
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Effects of dynamic Jahn-Teller distortions by Raman spectroscopy in the layered CMR manganite La(sub 2(minus)2x)Sr(sub 1+2x)Mn(sub 2)O(sub 7), x = 0.36

机译：动态Jahn-Teller畸变的拉曼光谱对层状CmR锰氧化物La（sub 2（负）2x）sr（sub 1 + 2x）mn（sub 2）O（sub 7），x = 0.36的影响

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The close interplay among charge, spin, and lattice degrees of freedom in the colossal magnetoresistive (CMR) manganite oxides is believed to play an important role in the transport mechanism in these itinerant ferromagnets. While the work on CMR materials has concentrated on the 3D perovskite manganites, the discovery of the layered compounds La(sub 2(minus)2x)Sr(sub 1+2x)Mn(sub 2)O(sub 7) as another class of CMR oxides provides a rich opportunity to explore the relationship between structure and transport properties on varying length and time scales in reduced dimensions. The crystal structure of the layered CMR compounds La(sub 2(minus)2x)Sr(sub 1+2x)Mn(sub 2) O(sub 7) is comprised of perovskite bilayers of corner-linked MnO(sub 6) octahedra forming infinite sheets. Doping of divalent cations such as Sr(sup 2+) gives rise to a mixed valent system were Jahn-Teller (JT) active Mn(sup 3+) and JT-inactive Mn(sup 4+) co-exist on the lattice. Among the current theoretical models of transport in the three-dimensional perovskite materials is the role of JT. This transport mechanism plays a fundamental role above the Curie temperature (T(sub c)). Indeed, localized lattice distortions have been observed experimentally above T(sub c) in the (La,Ca)MnO(sub 3) perovskite system. In this communication, the authors report resonant Raman spectroscopic measurements on a micro-crystalline sample of La(sub 1.28)Sr(sub 1.72)Mn(sub 2) O(sub 7) (x = 0.36). The measurements suggest discrete phonon modes for the Mn(sup 3+) and Mn(sup 4+) lattice sites, which may arise from either dynamic or static localization and the presence of Mn(sup 2+) defects in the lattice.

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