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Anisotropic Strain, Domain Structure and Charge Ordering in Epitaxial Pr1-xSrxMnO3 Films

Author: YinZhiZhen
Tutor: WuWenBin
School: University of Science and Technology of China
Course: Condensed Matter Physics
Keywords: Perovskite manganite Epitaxial thin films Oxygen vacancy Anisotropic stress Antiferromagnetic
CLC: O484.4
Type: PhD thesis
Year: 2009
Downloads: 140
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Since discovered giant magnetoresistance (CMR) in perovskite structure manganese oxide to arouse people's interest, not only because it has potential applications in addition, because of the type of oxide material is spin, charge, orbital and crystal lattice degrees of freedom interaction is a strongly correlated system, various interactions and the competition between them has resulted in complex electromagnetic and structural phase diagram, as well as a wealth of physical phenomena, such as charge-orbital ordering and phase separation, it to become one of the most active areas of today's condensed matter physics and materials science. The GMR film related electronic prototype devices, especially in the development of all-oxide devices significance. This paper, through the study of the manganese oxide system, the system studied regulation La 0.7 Ca 0.3 of MnO 3-δ films oxygen content and in air at room temperature in the diffusion of oxygen atoms in the film memory problems. Anisotropic stress is the decisive factor of the antiferromagnetic state appears in the film, and to explore the the antiferromagnetic film thickness effect, and the domain structure of the films with the thickness evolution, as well as analysis and discussion changing the doping concentration on the physical properties of the antiferromagnetic film systems. The main content of this paper is organized as follows: The first chapter introduces the research progress of the physical properties of giant magnetoresistance manganese perovskite oxide and epitaxial films. First, a review of manganese oxide history: some of the physical properties of the crystal structure and lattice distortion, the basic physical mechanisms (such as the double exchange interaction, Jahn-Teller effect) ordered phase, phase separation, charge ordering phase transition abnormalities, affecting charge ordered state stability factors. Then describes the thickness of the film stress effects, including lattice strain caused by lattice mismatch between the crystal structure, transport behavior, magnetic properties, thickness effect on the lattice parameters, the influence of the physical nature. The second chapter introduces the method of preparation and testing of samples of single-crystal thin films used in this experiment. The pulsed laser deposition prepared films principles and advantages of the technology. At the same time, X-ray diffraction techniques as well as magnetic and transport properties of measuring instruments. Chapter III, La 0.7 Ca 0.3 of MnO 3-δ / the LSAT (001) film, the oxygen content of the regulation system and The stability problem of the diffusion of oxygen atoms and oxygen content in the air at room temperature. The experiments show that after the oxygen content of the samples of the high-temperature vacuum annealing in the air at room temperature, the very unstable, oxygen atoms can diffuse into the compensation of oxygen vacancies in the film cause the Mn 4 / Mn 3 increase. With the sample is placed in the extension of the air time period, and the Curie temperature, the plane of the thin film, the lattice constant decreases the in-plane lattice constant, however, remain unchanged. But in the oxygen content of the hypoxic reduction prepared in the LCMO situ film in the air is very stable. Therefore, by adjusting the deposition oxygen pressure to control the oxygen content of the manganese oxide thin film is a stable and effective method. Chapter IV System LSAT (110) single crystal substrate is epitaxially grown on Pr 0.5 Sr 0.5 of MnO 3 film thickness effect and domain structure evolution with thickness. With decreasing temperature, PSMO / LSAT (110) film paramagnetic - ferromagnetic phase transition and ferromagnetic - antiferromagnetic order phase transition and is accompanied by a significant thermal hysteresis phenomenon. When the thickness increases, the Curie temperature of the film increases, the while antiferromagnetic intersect temperature reduced; antiferromagnetic ordered state stability decreases melting field decreases. Analyze the crystal structure of the film, and found that anisotropic stress causes the thin film structure by the tetragonal distortion of the rhombohedral system. At room temperature when the thickness is less than 12nm, the lower film Aeromonas monodomain monoclinic structure. With the increase in the thickness the PSMO films periodic domain structure, and gradually to the evolution of multi-domain, resulting in the increase in the degree of disorder of the film structure. Closely linked, it is the electrical transport properties and crystal structure of the thin film magnetic film domain structure changes in the thickness of the effect of the presence of the increase in the degree of structural disorder prompted weaken the antiferromagnetic state of the sample, the melting field decreases. Chapter V, System LSAT on the substrate of the different orientations of the epitaxially grown The Pr 1-x Sr x MnO 3 (0.47 ≤ x ≤ 0.60) the electromagnetic transport behavior of thin-film system, compare the doping concentration and anisotropic stress on the transport properties of the entire system. Due to the clamping effect of the substrate on the film, with the lower the temperature from room temperature, PSMO / LSAT (001) film only in T C at appeared paramagnetic insulating states - the phase change of the ferromagnetic metal state, However PSMO / LSAT (110) thin film samples in the cooling process has appeared in the paramagnetic insulating state - ferromagnetic metallic state and the ferromagnetic metallic state - antiferromagnetic insulating state is a phase transition. With Sr 2 increasing the doping concentration, the thin film of antiferromagnetic insulating state is more stable, the phase change temperature increased melting field increases. The cause above results may be due to the highly doped samples associated with the ferromagnetic weakened Jahn-Teller lattice distortions caused by the electron - phonon interaction enhanced electron localization tendency is more obvious.

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CLC: > Mathematical sciences and chemical > Physics > Solid State Physics > Thin Film Physics > The nature of the films
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