First-principles Theory of Thermal Effects in Spin Transport

该奖项支持旨在理解自旋相关输运中热效应的计算和理论研究和教育。众所周知，自旋无序会影响磁性材料中的电子结构并产生电子散射，但其对输运性质影响的具体机制却知之甚少。热声子对自旋相关输运的影响及其与自旋涨落的相互作用也很少受到关注。PI将使用第一性原理电子结构理论研究热自旋涨落和声子对磁性材料和异质结构的电子结构和输运性质的影响。本论文的主要研究方向如下：（1）研究热自旋涨落对半金属铁磁体及其与半导体界面电子结构的影响，以及对界面自旋注入的影响。自旋-轨道耦合对半金属自旋注入的影响也将被研究。(2)本文将研究MgO基磁性隧道结中隧穿磁电阻的温度依赖性机制，包括热自旋涨落和声子的影响。(3)本文将沿着研究电子掺杂铁磁半导体EuO的交换相互作用机制及其有限温度下的自旋输运性质。(4)铁磁金属的自旋无序电阻率将集中研究重稀土金属从Gd到Tm的序列的定量趋势，以及自旋无序和声子散射之间的相互作用导致的对Matthiessen规则的偏离。该项目将通过促进新的和更有效的磁电子器件的设计而产生更广泛的影响。并通过开发新的计算工具来研究有限温度下的磁性。研究将涉及研究生，他们将接受现代电子结构的教育，磁性和运输理论，并获得在使用和开发复杂的电子结构代码的经验。该奖项支持计算和理论研究和教育，旨在了解影响大块磁性材料中电流流动的物理机制和数百万原子的微小磁性结构。比人类头发的尺寸小一倍。在这些材料中，电子自旋起着重要的作用。电子可以看作是一个微小的磁铁。它的磁性与一种被称为自旋的内在量子力学性质有关。本研究的重点是计算通过这些磁性材料的温度依赖性电流。更好地理解电流如何流过磁性材料有助于信息系统的电子器件技术和新兴的未来电子器件技术，这些技术不仅利用现有器件的电子电荷，而且还利用电子自旋。这项研究将扩大我们预测材料性质的能力，仅从组成原子的身份开始。这有助于通过基于量子力学基本原理的计算机模拟来设计具有所需特性的材料的更广阔的视野。该研究涉及开发新的计算工具，用于研究温度相关的磁性，这可能与更广泛的计算材料研究社区共享。这个项目将为研究生提供先进材料理论和建模技术的教育经验，使用复杂的计算工具。

TECHNICAL SUMMARYThis award supports computational and theoretical research and education aimed at understanding thermal effects in spin-dependent transport. It is well known that spin disorder affects the electronic structure and generates scattering of electrons in magnetic materials, but the specific mechanisms of its influence on the transport properties are poorly understood. The influence of thermal phonons on spin-dependent transport and its interplay with spin fluctuations have also received little attention.The PI will investigate the effects of thermal spin fluctuations and phonons on the electronic structure and transport properties of magnetic materials and heterostructures using first-principles electronic structure theory. This research will pursue several directions: (1) The effect of thermal spin fluctuations on the electronic structure of half-metallic ferromagnets and their interfaces with semiconductors, as well as on the spin injection across these interfaces, will be investigated. The effect of spin-orbit coupling on spin injection from half-metals will also be studied. (2) The mechanisms of temperature dependence of tunneling magnetoresistance in MgO-based magnetic tunnel junctions will be studied, including the effects of thermal spin fluctuations and phonons. (3) The mechanisms of exchange interaction in electron-doped ferromagnetic semiconductor EuO will be studied, along with its spin transport properties at finite temperatures. (4) Spin-disorder resistivity of ferromagnetic metals will be investigated focusing on the quantitative trends in the sequence of heavy rare-earth metals from Gd to Tm, and on the deviations from Matthiessen's rule resulting from the interplay between the spin-disorder and phonon scatterings.The project will have broader impacts by facilitating the design of new and more efficient magnetoelectronic devices, and through the development of new computational tools for the studies of finite-temperature magnetic properties. Research will involve graduate students, who will be educated in modern electronic structure, magnetism and transport theory and gain experience in the use and development of sophisticated electronic-structure codes.NON-TECHNICAL SUMMARYThis award supports computational and theoretical research and education aimed at understanding the physical mechanisms that affect the flow of electric current in bulk magnetic materials and tiny magnetic structures of atoms some million times smaller than the size of a human hair. These are materials, in which the electron spin plays an important role. An electron can be thought of as a tiny magnet. Its magnetic properties are related to an intrinsically quantum mechanical property known as spin. The focus of this research is on calculating the temperature dependent current flow through these magnetic materials. A better understanding of how current flows through magnetic materials contributes to electronic device technology for information systems and emerging future electronic device technologies that exploit not only the electron charge as existing devices do now, but also the electron spin. This research will expand our ability to predict the properties of materials starting only from the identities of the constituent atoms. This contributes to the broader vision of being able to design materials with desired properties through computer simulations based on fundamental principles of quantum mechanics.The research involves developing new computational tools for the studies of temperature dependent magnetic properties, which may be shared with the broader computational materials research community. This project will provide educational experiences for graduate students in advanced materials theory and modeling techniques using sophisticated computational tools.