Browsing by Author "Aydogdu Kuru, Gülgün Hamide"

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    Tuning transport, magnetic and structural properties of La0.5Ca0.5MnO3 films by epitaxial strain
    (2009) Aydogdu Kuru, Gülgün Hamide; Maier, Joachim (Prof. Dr.).
    The perovskite-type doped rare earth manganites have a rich phase diagram due to a delicate balance between several ordering mechanisms such as charge-, orbital- as well as spin order superimposed to lattice effects caused by distortions of the oxygen octahedra surrounding the Jahn-Teller ion Mn3+. Chemically homogeneous materials can appear as electrically inhomogeneous in locally separated electronic phases. This phase separation in manganites is very sensitive to external perturbations such as high magnetic fields and epitaxial strain. In this study, La0.5Ca0.5MnO3 -LCMO- (at the boundary between ferromagnetic (FM) metallic and charge-ordered antiferromagnetic (AFM) insulator) thin films are chosen as an example to investigate the competition between these different phases. LCMO films of various thicknesses are deposited on (001), (111) SrTiO3, (001) SrLaGaO4 and SrLaAlO4 substrates by the pulsed laser deposition method. Characterization of the structural, electrical and magnetic properties of the films is performed by X-ray diffraction, atomic force microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, resistivity and magnetization measurements. The present study shows that it is possible to stabilize a wide range of the electronic phases from an insulator to metallic and vary the magnetization values more than an order of magnitude using the substrate material as a knob to modify the film properties. Furthermore, it is found out that the oxygen stoichiometry, changed by heat treatments in vacuum or under O2 flow at a constant background pressure, has a strong effect on the structural, magnetic and electronic properties of LCMO thin films. In the as deposited state, the films have a certain density of oxygen vacancies determining the physical properties in addition to cation composition and epitaxial strain.