Studies On The Preparation And Physical Properties Of Low Dimensional Manganites

As a typical example of the strongly correlated electron systems, perovskite manganites with colossal magnetoresistance effect (CMR), have been an perennial hot topic of the condensed matter physics. It is due to not only their potential technological applications in magnetoelectronics, but also their abundant physical characteristics originating from the strong correlation of the multiple quantum parameters, such as the sensitivity to external fields, metal-insulator transition, phase separation and so on. Various properties make the studies of magnanites under size confinement quite fascinating, and the rapid development of the synthetic methods have inspired new avenues in these researches. The present thesis, focused on the low dimensional manganites system, has carried out a series of researches on the synthesis of manganites with different dimensions and the corresponding properties studies. The details are as follows:In Chapter1, we introduced the basic properties of manganites with colossal magnetoresistance effect, including the crystal structure, electrical structure, multiple ordering phases, phase separation, etc. and the related progresses in the low dimensional manganites system.In Chapter2, high quality La0.33Pr0.344Ca0.33MnO3films with periodic structure of several micrometers were obtained via the micro-nanomachining method The magnetotransport studies demonstrate that the distinct resistance hopping, with the value variation can even up to several orders, was observed in the resistance curves, and could be adjusted to some extent by temperature, magnetic field and current. Such phenomenon has never been seen in the narrow stripe samples of the same size. The modulation of the periodic structure gives a new approach for the understanding of the phase separation in the manganites and the promotion of the technological applications prospects.In Chapter3, we have successfully synthesized the one dimensional manganites with complicated compositions of Pr0.6Ca0.4MnO3and La0.33Pr0.34Ca0.33MnO3via the combination of the chemical vapor deposition and pulsed laser deposition method. The structural and morphological investigation showed that the as-synthesized La0.33Pr0.34Ca0.33MnO3exhibits good single crystal properties and uniformly size distribution, while the Pro.6Cao.4Mn03are of the polycrystalline nanowire structures. Significantly, compared with the bulk materials, the charge ordered phase is suppressed totally and the non long-range ferromagnetic order emerge.In Chapter4, we have successfully synthesized the La0.67Sr0.33MnO3/MgO nanorod arrays using MgO nanorod arrays as template. Based on such novel structure, we obtained obviously magnetoresistance effect over a wide temperature range from10K to300K. By comparing of various samples prepared under different conditions, we further conformed the weak links between the neighboring nanorods are critical to gain such high low field magnetoresistance effect.In Chapter5, we give a brief summary of results obtained in the literature.