COLLABORATIVE RESEARCH: QUANTUM SPIN CHAINS. EXTENT AND PERSISTENCE OF MAGNETIC INTERACTIONS AS A FUNCTION OF LENGTH AND SPIN

非技术性这项研究是在有机材料和低维系统领域。它包括制造长度为7到200个原子的超短链，以检验理论模型和探索新的磁性的出现。这项研究对低维系统的磁性行为提供了更广泛和更深入的理解，并可能对新一代自旋电子器件的发展产生直接影响。这项研究具有积极的教育成分。该项目包括每学期两名为博士论文主题进行研究的研究生和两名物理本科生。在这些活动中，学生首先接受同步加速器和中子设施的培训，并接触到最先进的先进实验技术。与该项目相关的社区外联工作包括与圣安东尼奥学区的高中建立伙伴关系，并使用滑稽的方法制作与纳米技术有关的不同主题的短片。这些努力的目的是增加高中生的科学知识，并为美国各地的科学教育工作者提供工具。技术本研究旨在研究磁性1D链中的三个基本问题：1)作为链的长度和缺陷的函数，确定短程和长程磁相互作用的程度和持久性；2)控制和调制沿链的自旋；以及3)探索不同组成的磁性/非磁性金属链中的邻近效应。为了实现这些目标，PI开发了一种制造一维链的宏观阵列的方法，该方法允许精确控制其长度、组成和自旋。具体地说，这项研究集中在~7到200个原子长的超短(和探索不足的)链上。利用金属酞菁(MPC)超晶格(SLS)，用有机分子束外延(OMBE)方法生长了单原子链和变组成链。MPC是一类平面有机分子，分子中心有一个金属原子，周围环绕着有机载体。许多金属离子(铁、镍、铜、钴和锰)可以被取代，形成许多具有不同电子(自旋)构型和物理性质的等结构化合物。当用OMBE生长时，这些分子面对面地堆叠在一起，形成一维金属链。分子链的取向和长度可以分别由衬底的选择和沉积MPC层的厚度来控制。此外，使用SL结构，可以通过插入其他磁性和非磁性MPC层来改变链组成和自旋。该项目包括在宽广的温度/场中进行结构表征(X射线衍射和高分辨电子显微镜)和磁性测量(SQUID、VSM和交流磁化率)。同步加速器技术，如XMCD，被用来获得元素选择的磁性测量和形成不同组成链的金属离子的电子组态。NEXAFS和DFT计算允许确定这些元素的自旋组态。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technicalThis research is in the field of organic materials and low-dimensional systems. It consists of the fabrication of ultra-short chains of 7 to 200 atoms in length, to test theoretical models and explore the emergence of new magnetic properties. This study provides a broader and deeper understanding of the magnetic behavior of low-dimensional systems and may have a direct impact on the development of a new generation of spintronic devices. This research has an active educational component. The project involves two graduate students who perform research for their Ph.D. thesis topic and two physics undergraduate students per semester. During these activities, students receive training at first synchrotron and neutron facilities and are exposed to state of the art advanced experimental techniques. Community outreach efforts associated with this project involve a partnership with high schools in San Antonio school districts and the production of short videos on different topics related to nanotechnology using a comical approach. These efforts are aimed to increase scientific knowledge in high school students and provide tools for science educators across the United States.TechnicalThis research is aimed to study three fundamental problems in magnetic 1D chains: 1) the determination of the extent and persistence of short- and long-range magnetic interactions as a function of the chain's length and defects, 2) the control and modulation of the spin along the chains, and 3) the exploration of proximity effects in varying composition magnetic/non-magnetic metal chains. To achieve these objectives, the PIs have developed a method for the fabrication of macroscopic arrays of 1D chains that allow precise control of their length, composition, and spin. Specifically, this research focuses on the ultra-short (and poorly explored) chain of ~7 to 200 atoms long. Monoatomic and varying composition chains are grown by Organic Molecular Beam Epitaxy (OMBE) using metallo-phthalocyanine (MPc) superlattices (SLs). MPcs are a family of planar organic molecules with one metal atom located in the molecule's center surrounded by organic support. Many metal ions (Fe, Ni, Cu, Co, and Mn) can be substituted into the MPc giving rise to many isostructural compounds with different electronic (spin) configurations and physical properties. These molecules stack face-to-face giving rise to 1D metal chains when grown by OMBE. The orientation of the chain and its length can be controlled by substrate choice and thickness of the deposited MPc layer respectively. Moreover, using a SL structure, the chain composition, and spin can be varied by intercalating other magnetic and non-magnetic MPc layers. This project includes structural characterization (XRD and HRTEM) and magnetic measurements (SQUID, VSM, and AC susceptibility) in a broad temperature/field. Synchrotron techniques such as XMCD are used to obtain element-selective magnetic measurements and electronic configuration of the metals ions forming the varying composition chains. NEXAFS and DFT calculations allow determining the spin configuration of these elements.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.