Static and dynamic spin properties in antiferromagnetic thin films and heterostructures

非技术描述自旋电子学是一个活跃的研究领域，它着眼于将电子的自旋用于信息处理和存储技术。反铁磁性材料对于加速自旋电子学的发展具有重要意义，因为它们比铁磁材料具有独特的优势，因为它们具有更快的自旋进动动力学和不存在自发磁矩。然而，关于反铁磁性薄膜的研究一直很少。在这个项目中，由世界领先的专家组成的研究团队利用高质量的材料合成、使用太赫兹源检测反铁磁自旋电流、反铁磁域成像和太赫兹时间域谱，阐明了薄膜反铁磁材料中的重要和具有挑战性的基本问题。实验工作得到了理论计算的补充。研究生和本科生，包括那些来自代表人数不足的少数群体的学生，都接受了未来在信息技术行业就业所需的知识和技能的培训。由于薄膜反铁磁体具有更快的自旋动力学和不存在自发磁矩的数量级，因此在获得基本的静态和动态自旋性质方面面临着巨大的挑战，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，许多具有挑战性的问题都是通过使用一套内部开发的或通过与世界领先专家合作获得的强大功能来解决的。包括脉冲激光沉积和分子束外延的外延薄膜和异质结生长，通过自旋Seebeck效应和使用固态太赫兹源和自由电子激光的太赫兹自旋泵浦检测反铁磁自旋电流，用扫描金刚石氮空位中心显微镜进行反铁磁畴成像，以及太赫兹时间域谱。结合密度泛函理论对反铁磁材料的性质进行了分析。具体地说，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有序参数；(2)通过热和共振产生、传输和电检测反铁磁薄膜中的自旋电流，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性质。

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.