Static and dynamic spin properties in antiferromagnetic thin films and heterostructures

自旋电子学是一个活跃的研究领域，它着眼于利用电子的自旋用于信息处理和存储技术。反铁磁材料是加速自旋电子学发展的重要材料，因为它们具有比铁磁材料更快的自旋进动动力学和不存在自发磁矩的独特优势。然而，对反铁磁薄膜的研究却很少。在该项目中，由世界领先专家组成的研究团队阐明了使用高质量材料合成薄膜反铁磁材料中重要且具有挑战性的基本问题，使用太赫兹源检测反铁磁自旋电流，反铁磁畴成像和太赫兹时域光谱。实验工作与理论计算相辅相成。研究生和本科生，包括来自代表性不足的少数民族的学生，都接受了信息技术行业未来就业所需的知识和技能培训。由于自旋动力学快的数量级和自发磁矩的缺乏，薄膜反铁磁体在获得基本的静态和动态自旋性质方面面临巨大的挑战，例如反铁磁有序温度，磁各向异性，磁振子色散和阻尼参数。在这项研究中，使用内部开发的一套强大功能或通过与世界领先专家的合作解决了许多具有挑战性的问题。这些包括外延薄膜和异质结构生长的脉冲激光沉积和分子束外延，检测反铁磁自旋电流通过自旋塞贝克效应和太赫兹自旋泵使用固态太赫兹源和自由电子激光，反铁磁畴成像与扫描金刚石氮空位中心显微镜，和太赫兹时域光谱。结合密度泛函理论分析了反铁磁材料的性质。具体而言，该项目遵循以下计划：（1）生长高质量的外延反铁磁薄膜和异质结构，以准确确定和有效地操纵反铁磁序参数：（2）在反铁磁薄膜中产生、传输和电学检测自旋电流，包括热和共振，以获得各向异性、交换强度和阻尼参数;以及（3）通过生长和外部刺激控制反铁磁静态和动态特性。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical DescriptionSpintronics is an active field of research which looks at utilizing the spin of electrons for use in information processing and storage technology. Antiferromagnetic materials are important for speeding up development of spintronics because they have unique advantages over ferromagnetic materials due to their much faster spin precession dynamics and absence of spontaneous magnetic moment. However, research on antiferromagnetic thin films has been scarce. In this project, the research team comprising world leading experts elucidates important and challenging fundamental issues in thin film antiferromagnetic materials using high-quality materials synthesis, detection of antiferromagnetic spin currents using terahertz sources, antiferromagnetic domain imaging, and terahertz time-domain spectroscopy. The experimental work is complemented with theory calculations. Graduate and undergraduate students including those from including underrepresented minorities are trained with the knowledge and skills needed for future employment in the information technology industry. Technical DescriptionDue to the orders of magnitude faster spin dynamics and absence of spontaneous magnetic moment, thin film antiferromagnets present tremendous challenges in obtaining basic static and dynamic spin properties such as the antiferromagnetic ordering temperature, magnetic anisotropy, magnon dispersion, and damping parameter. In this research, a number of challenging issues are tackled using a suite of powerful capabilities developed in-house or available through collaborations with the world leading experts. These include epitaxial thin film and heterostructure growth by pulsed laser deposition and molecular beam epitaxy, detection of antiferromagnetic spin currents via spin Seebeck effect and terahertz spin pumping using both solid state terahertz source and free-electron laser, antiferromagnetic domain imaging with scanning diamond Nitrogen Vacancy-center microscope, and terahertz time-domain spectroscopy. The antiferromagnetic material properties are analyzed in conjunction with density functional theory. Specifically, the project follows the following plan: (1) grow high-quality epitaxial antiferromagnetic thin films and heterostructures for accurately determining and efficiently manipulating the antiferromagnetic order parameter; (2) generate, transport, and electrically detect spin currents in antiferromagnetic thin films both thermally and resonantly to obtain anisotropy, exchange strength, and damping parameters; and (3) control antiferromagnetic static and dynamic properties via growth and external stimuli.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.