In this study, the samples were prepared with mixed two colossal magnetoresistance materials and sintered at high temperature. Then analysis the affect of doping concentration in MR effect, and applied it on the magnetic thin film. X-ray diffraction images and SEM images were used to show the lattice structure and grain boundary. The RT curves show the position of Tp temperature ,and pH curves shows the characteristic of MR.

The sample are prepared by co-sintering the pure 3D ferromagnetic colossal magnetoresistance La0.7Sr0.3MnO3 (113) and the 2D spin-glass magnetic insulator La0.7Sr0.3MnO3¡ESrO (214) with an ordered 2D magnetic-insulator superstructure. Increase the magnetic scattering and collision probabilities of the carries on the interface of the two kinds of CMR materials. The LFMR is enhanced by the electron scattering between these two phases. (La0.7Sr1.3MnO4)x / ( La0.7Sr0.3MnO3)1-x composites with x=0.1¡B0.15¡B0.2¡B0.3¡B0.5 have been fabricated by sintering the mixture of the pure La0.7Sr0.3MnO3 (n=¡Û) and the La0.7Sr1.3MnO4(n=1) at 1400 for 24 hours. Part of the 113 phase reacted with 214 phase during the 1400¢J annealing process and formed the antiferromagnetic phase , La1-2ySr2+2yMn2O7 (327), with the unknown content, y. The £l-H curve shows the magnetic interaction between the interface grain numbers of the 113 and 327 affects the effect of the low field magnetoresistance effect.

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The low-field magnetoresistance of colossal magnetic thin film can be enhanced by proton implantation. Compare with the as grown sample, the implantation samples has lower transition temperature and higher resistivity. By the hall measurement, we can get the carrier type and carrier concentration. The hall magnetoresistance (MRH) is much greater than the longitude magnetoresistance (MR). Chapter 1. Introduce experiment purpose and expected results. Chapter 2. Introduce the basic theorem of colossal magnetic materials. Chapter 3. The steps of experiment. Chapter 4. Results and discussion. Chapter 5. The conclusion.

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Abstract It is know that the crystal structure and the magnetic ordering in La1-xAxMnO3(A=Ca,Sr,Ba) may disrupted by introducing various defect. This disorder weakens the Hund coupling and, thus, the double-exchange interaction between Mn3+ and Mn4+. Combining with John-Teller distortion enhanced by the defects, the magnetoresistance (MR) effect is enhanced. Up to date, the generated defects were mostly columnar defects or chemical substitution defects. In this study we generated different type of defect, point defects, and inrestigate its effect on MR effect. La0.7Sr0.3MnO3 and La0.7A0.3MnO3 films were deposit on LaAiO3 (001) and SrTiO3 (001) substrates by pulse laser deposition technique. Films were patterned with a standard photolithography. Point defects were introduced by irradiated high (1.7 and 3MeV) and low (10KeV) energy protons. We found that, the low dose sample exhibits both conductivity and the low field MR enhancement. Which were believed due to introduce acceptor level and the magnetic structure defects. When the dose was high, the structure defects leaded strong scattering effect that lowed the conductivity. The MR in high dose sample was also enhanced near by transition temperature.

Abstract Recent progress in oxide perovskite thin-film technology has led to the discovery of a large negative magnetoresistance in doped manganate perovskite thin films. These films may have potentials for magnetic random access memory (MRAM) and magnetic sensors. Therefore, the research of magnetoresistance has been attracted a lot of attentions. The magnetoresistance is directly related to the microstructure. In an application point of view, the ulta-thin film may be more appropriate compares with those utilizing with thicker films. In this paper, we report the detail results of electrical property of La0.67Ca0.33MnO3 (LCMO) films related with their microstructure. The La0.67Ca0.33MnO3 (LCMO) films were deposited on (001) STO substrate with RF sputtering technique. The working pressure was maintained at 100m torr and the growth temperature was kept at 750¢J. After growth the films was annealed at 850¢J for 1 hour in a 500 torr O2 annealing environment. The growth time was 3mins.¡B6mins. and 12mins. respectively. The crystal structure of LCMO films were characterized with X-ray diffraction (XRD). The surface morphology of LCMO films were observed by scanning electron microscope (SEM) and the interface of microstructure between LCMO films and STO substrate were investigated by transmission electron microscope (TEM). Finally the M-I transition temperature were evaluated with 4-point probe at the temperature range from 300K down to 77K. The results show that the LCMO films were amorphous when the growth time was in 3 mins. The microstructure of the film gradually became poly-crystal and had a (001) prefer orientation after the growth time increasing to 6 mins. The grain size of the 12 mins growth film was at 40-50 nm scale. The Curie temperature and magnetoresistance change of these films were increased as the degree of crystallization of these films became better.

In the 4d transition metal oxides, the extension of the 4d orbitals leads to comparable and thus competitive kinetic and coulomb energies. As a result, small perturbations can induce significant changes in their physical properties, giving rise to a class of exotic phenomena that are rarely found in other materials. The ruthenates materials with readily tunable parameters open an avenue to study the strong electronic correlation in the rarely explored territory: the 4d transition metal oxides. The bilayered system, Ca3Ru2O7, belongs to the Ruddlesden-Popper series in which the physical properties are intimately linked to the lattice degrees of freedom. Ca3Ru2O7, with its quasi-2D and severe structure distortion, is believed to be placed in a unique position at which the role of orbital degrees of freedom is highlighted. The system displays strikingly different behaviors when the field is applied along different crystalline axes. A ferromagnetic (FM) state with full spin polarization is achieved for B||a-axis, but colossal magnetoresistance is realized only for B||b-axis by avoiding the ferromagnetic state. In addition, for B rotating within the ac-plane, slow and strong SdH oscillations periodic in 1/B are observed for T.1.5 K in the presence of metamagnetism. For B|| [110], oscillations are also observed but periodic in B (rather than 1/B) and persist up to 15 K. These properties together with highly unusual spin-charge-lattice coupling near the Mott transition (48 K) are driven by the orbital degrees of freedom. Complex thermodynamic properties are also observed in the other ruthenates system such as Sr4Ru3O10 and Pr3RuO7. The Sr4Ru3O10 is a triple-layered system that shows a dedicate balance between fluctuations and order. Besides the anomaly at TC=102K, anomalous behavior at low temperatures are also observed in the thermal study, indicative of an unusual magnetic order in this material. The Pr3RuO7 shows one-dimensional structure with zig-zag chain of corner sharing RuO6 octahedra running in parallel with the rows of edge-shared PrO8 pseudo-cubes. Magnetic and thermal properties studies on its single crystals indicate that the exchange interaction is strongly anisotropic. A Schottky-type anomaly at low temperature suggests that the gorderedh chain Pr ions are still sensitive to a crystal field.

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