Investigation of Depth-Dependence in Strongly Correlated Magnetic Oxides by Integrated Experiments and Theory

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Nontechnical Abstract:Surfaces of materials have different properties than bulk. Such differences can be manipulated, eliminated or enhanced to improve desired properties and create better, more useful devices. This work focuses on a class of magnetic thin films which are hoped to provide wide array of future applications in computing, electronics and even power generation. A strong collaboration of theory and experiment will benefit the quality of planned effort by providing a way to describe the observations theoretically and build models of observed variations of material properties as a function of depth. This project will support the education of PhD students in advanced vacuum deposition and theoretical and characterization techniques; a proven approach providing excellent training opportunities resulting in productive scientific careers in academic and technology settings. The expected increased physical understanding of magnetism and interfacial properties in thin films from these studies will be particularly relevant to technological applications which incorporate thin magnetic films, such as magnetic recording, spin generation, spin manipulation and/or spin detection. An improved understanding of surface and interface properties will allow smaller devices using less materials, higher energy efficiency and faster communication.Technical Abstract:Magnetic and other properties at surfaces and interfaces are often different from the bulk, which can have significant impact on technologies relying on these properties. To develop enhanced interfaces and potentially new interfacial phenomena, strong competition is favorable. Strongly correlated oxides, with their competition between charge, spin and orbital degrees of freedom offer many promising systems that may allow these tunable parameters. This project will study strongly correlated magnetic LaxSr1-xMnO3 (LSMO) thin films, which have been widely proposed for applications such as tunnel junctions and solid oxide fuel cells. Using scanning transmission electron microscopy and newly developed depth-dependent x-ray absorption analysis to model the magnetization and other properties with depth, the deviation of these parameters from bulk values at both the top and bottom interfacial layers of the thin film will be quantified. Improvements or degradation in the interfacial properties will be linked with the other measured parameters that vary in order to determine in collaboration with dynamical mean field theory the contribution from each factor. The project's focus on comparing the theoretical and experimental depth-dependent properties near surfaces and interfaces is expected to provide valuable insight into the properties of magnetic thin films and help answer questions about the primary contributing factors to the manifestations of magnetic properties at LSMO complex oxide surfaces and interfaces, the effect of adjustable strain on LSMO thin film properties, and general behaviors of interfacial properties in strongly correlated systems. These outcomes can be expected to allow optimization of both material choice and parameters for various magnetic applications such as computer memory, magnetic sensing and energy scavenging. The project will support the education of PhD students in advanced vacuum deposition, theoretical and characterization techniques, which have been proven to be excellent training for productive scientific careers in academic and technology settings.