Preparation And Physical Properties Of Sr₂FeMoO₆ Composite System

Double perovskite-type oxide Sr₂FeMoO₆ has become one of the extremely active role of front research areas in both material physics and condensed matter physics for its room temperature-low magnetic field magnetoresistance effect. Strongly correlated electronic system showed that, the grain boundary have important impact on the electron transportation behavior in multi-crystalline material, the interfacial state and grain size largely determine the physical performance. The microstructure in thin film with greater scalability rather than bulk material can be easyly adjusted. In this paper, double perovskite-type oxide Sr₂FeMoO₆ thin film was prepared respectively by sol-gel and electronphoresis deposition method. And then, Sr₂FeMoO₆ thin film composite syetem and Sr₂FeMoO₆ grain composite system series of samples were prepared though sol-gel method, while different nature and quantity second phase were introducted with Sr₂FeMoO₆ as the matrix phase. After that, the samples were characterized by XRD, SEM, AGFM, PPMS respectively in meaning of the lattice structure, microstructure, magnetic and electrical transport properties, thus providing some basics theoretical research and experimental conditions.This study includes the following aspects:1 Double perovskite-type oxide Sr₂FeMoO₆ related konwledge was introduced systematically and elaboratly. The microstructure, electricial transport, magnetic properties of Sr₂FeMoO₆, and the main research progress in both particle type and thin film type of double perovskite-type oxide Sr₂FeMoO₆ composite system. Based on the topic of Sr₂FeMoO₆ composite system, this thesis is on detailed work.2 Sr₂FeMoO₆ thin film was perpared respectively on monocrystalline silicon Si(100) and strontium titanate SrTiO₃(100) substrate by sol-gel method and on monocrystalline silicon Si(100) and single crystal copper Cu(100) substrate through electrophoresis deposition. X-ray diffraction analysis shows that, all the samples were single-phase with better crystallization. SEM images indicate that all the sampels surface were smooth, particles growed uniform distributed with sharp lightness and connectivity.3 A series of Sr₂FeMoO₆ particle composite syetem and Sr₂FeMoO₆ thin films composite system were prepareed by sol-gel method. X-ray diffraction and scanning electron microscopy showed that the second phase materials with nanometer were introduced into the grian boundary of Sr₂FeMoO₆ matrix phase, in this simultaneity, the lattice structure of the matrix and second phase did not changed, the Sr₂FeMoO₆ phase and second phase with different nature and content materials were well complex in composite system, so as to achieve the chang of grain boundaries state in the composite system in the purpose of the study of electro-magnetic properties.4 The M-H curves of the samples were determined by AGFM. The magnetic moment increased with the more amount of the second phase, at the same time exieting a extrema for the same complex type, when the quantity x=0.09, thin film compound system were the strongest magnetic as the particals composite system. For the different second phase, the magnetic moment of sample did not entirely according to the granule size changed disciplinnarian. The M-T curves in 500Oe of the thin film composite system sample were confirmed through PPMS, the magnetic moment presented manifold changes. Based on the model of double exchang theory, this thesis qualitative explaned the mechanism of magnetic of Sr₂FeMoO₆ partical and thin film composite system.5 The electrical resistance of the samples were measured in conformity four probe principle. All the samples have semiconductor conduction behavior performance, the second phase made the materials have more larger eletrical resisitance. In the partical composite system, when the composite quantity x=0.09, the resistivity have the extremum in all different kind of complex combination. In the thin film composite system, the resistivity was related to the grain size and electron structure. Sr₂FeMoO₆ composite materials, due to the existence of different grain boundary state, the transport properties were decided by the spin polarization electrons tunneling or scattering.