Study Of The Competition Of Ordering Phase And Quantum Transition In Strongly Correlated Manganites

The study of the manganites, widely known belonging to strongly correlated electron systems, that exist many novel and interesting physical phenomena and complex physical mechanism is among the active and attractive areas of research within the area of physics and information material physics. Significantly, the strong coupling and competition among the spin, charge, orbital, and lattice degrees of freedom in these systems can induce a wide variety of newly novel phenomena such as insulator-metal transition, orderings and phase separation etc. All these challenge the traditional understanding of physics and information science and will provide newly subject for the physicist, material scientist and information scientist. A lot of related new physical phenomena and concepts have been brought forward, which will arouse a revolution of some basic subjects (such as strongly correlated systems, spinelectronics physics) and the information technology in the future. This probably makes strongly correlated manganites the one of the hotspots in the field of condensed matter physics in the 21st century. In this dissertation, based on the preparation of high quality single crystal and polycrystalline samples, the typical phase-separated La5/8-xPrxCa 3/8 MnO3 and half doped (La,Pr)0.5Ca0.5MnO3 systems were investigated in magnetic fields. The correlation between low temperature phase separation and novel step-like transport, and the correlation among ordering parameters such as charge ordering and orbital ordering etc. were studied Meanwhile, the charge/spin/orbital ordering structure, the mechanism of magnetic induced spin reorientation/carrier delocalization, and the possible quantum spin/orbital transition were studied in these systems. The content of the dissertation are divided into six chapters and main results are summarized as follows.The first chapter describes the content status and progress of the studies concerning the strongly correlated manganites and correlative spin electronic physics, stressing on the phase separation in the mananites, the mechanism of the colossal...