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

摘要：材料表面具有不同于本体的特性。这些差异可以被控制、消除或增强，以改善所需的性能，并创造出更好、更有用的设备。这项工作的重点是一类磁性薄膜，它有望在计算、电子甚至发电方面提供广泛的未来应用。理论和实验的强有力合作将有助于提高计划工作的质量，因为它提供了一种从理论上描述观测结果的方法，并建立了观测到的材料特性随深度变化的模型。该项目将支持博士研究生在先进的真空沉积和理论和表征技术的教育；一种行之有效的方法，提供优秀的培训机会，从而在学术和技术环境中产生富有成效的科学事业。这些研究增加了对薄膜中磁性和界面性质的物理理解，这将与结合磁性薄膜的技术应用特别相关，例如磁记录、自旋产生、自旋操纵和/或自旋检测。对表面和界面特性的更好理解将使更小的设备使用更少的材料，更高的能源效率和更快的通信。技术摘要：表面和界面的磁性和其他性质通常与体不同，这可能对依赖于这些性质的技术产生重大影响。为了开发增强的界面和潜在的新界面现象，激烈的竞争是有利的。强相关氧化物在电荷、自旋和轨道自由度之间的竞争提供了许多有希望的系统，这些系统可能允许这些可调参数。该项目将研究强相关磁性LaxSr1-xMnO3 （LSMO）薄膜，该薄膜已被广泛提出用于隧道结和固体氧化物燃料电池等应用。利用扫描透射电子显微镜和新开发的深度依赖x射线吸收分析来模拟磁化和其他特性随深度的变化，这些参数与薄膜顶部和底部界面层的体积值的偏差将被量化。界面性质的改善或退化将与其他变化的测量参数联系起来，以便与动态平均场理论合作确定每个因素的贡献。该项目的重点是比较表面和界面附近的理论和实验深度相关的性质，预计将为磁性薄膜的性质提供有价值的见解，并有助于回答有关LSMO复合氧化物表面和界面上磁性表现的主要影响因素，可调应变对LSMO薄膜性质的影响的问题。强关联体系中界面性质的一般行为。这些结果可以预期为各种磁性应用（如计算机存储器，磁感应和能量清除）的材料选择和参数优化。该项目将支持博士研究生在先进的真空沉积，理论和表征技术方面的教育，这些技术已被证明是在学术和技术环境中富有成效的科学事业的优秀培训。

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.