Magnetism and Dynamics in Atomic Clusters

原子团簇中的磁性和动力学

• 批准号: 0405203
• 负责人: Louis Bloomfield
• 金额: $ 33万
• 依托单位: University of Virginia Main Campus
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-07-15 至 2008-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0405203&HistoricalAwards=false
• 关键词: Magnetism; Dynamics; Atomic; Clusters

Aggregates of between 2 and 1000 atoms make an excellent laboratory in which to study the static and dynamic properties of finite-systems. Among the most intriguing of those properties are magnetic order, which is extremely sensitive to structure and bonding, and the crossover behaviors that are analogous to bulk phase transitions, particularly the melting and freezing transitions. This individual investigator award supports two experimental projects in such clusters. The first project will explore the evolution of magnetism and magnetic properties with size in clusters of a wide range of materials, including those that are, in the bulk, ferromagnetic, antiferromagnetic, and nonmagnetic. The reduced dimensionalities of these systems and their high surface-to-volume ratios favor enhanced magnetic ordering and unusual couplings between their magnetic and spatial structures. The experiments to be performed will use magnetic deflection to measure effective magnetizations in the clusters and, in concert with theoretical models, to understand the magnetic characteristics of these particles. The second project will examine the time evolution of isolated, thermally excited clusters as they undergo spontaneous thermal isomerization. The experiments will be performed using pump-probe techniques with picosecond and femtosecond laser pulses to follow the structural and energetic evolutions of such clusters. In addition to watching the crossover from the low temperature solid-like phase to a liquid-like phase at high temperatures, these experiments will explore the roles of classical and quantum dynamics in describing the shape changing process. Both experiments involve cutting edge vacuum, electronic, laser, and optical technology and will prepare the graduate students taking part in this research for either academia or industry.Atomic clusters offer a conceptual bridge between the worlds of individual atoms and those of bulk materials. Consisting of between 2 and 1000 atoms, these tiny particles represent a middle ground in which to study the growth of bulk behaviors out of the simpler behaviors of atoms and molecules. Issues to explore with increasing particle size include both basic properties (e.g. magnetism) and phase transitions (e.g. melting and freezing). As technology pushes toward ever smaller dimensions, a clear understanding of such tiny systems is becoming a practical necessity. This individual investigator award supports two experimental projects that address this middle ground. The first project will explore the evolution of magnetism and magnetic properties with size in clusters of both the traditional magnetic metals (iron, cobalt, nickel) and the more unusual elements (rare earths, chromium, rhodium). With most of their atoms on their surfaces, these clusters are often unusually magnetic and have exotic thermal and structural characteristics. The experiments to be undertaken will measure the magnetic and thermal properties of a wide range of clusters and seek to identify systems with conceptually and/or technologically important magnetic characteristics. The second project will examine the time evolution of clusters that contain enough thermal energy to change their shapes even in the isolation of vacuum. Neither truly solid nor truly liquid, these shape-changing systems offer insight into the complexities of ultra-small systems in thermal environments. The experiments to be performed will use ultrafast laser pulses to watch the clusters change shape in real time and will look for both the familiar classical features of melting and freezing and the less familiar quantum features common in the atomic-scale world. Of particular interest is the surprising ease with which tiny particles rearrange thermally, a factor that inevitably shortens the short life spans of many tiny technological structures. Both efforts will involve cutting edge experimental techniques and will provide the students involved with skills and training that will prove useful in either academia or industry.

2 到 1000 个原子的聚集体是研究有限系统静态和动态特性的绝佳实验室。这些特性中最有趣的是磁序，它对结构和键合极其敏感，以及类似于体相变的交叉行为，特别是熔化和凝固转变。 该个人研究者奖支持此类集群中的两个实验项目。第一个项目将探索磁性和磁性的演变，以及各种材料簇尺寸的变化，包括那些大块的铁磁性、反铁磁性和非磁性的材料。这些系统的降维及其高表面体积比有利于增强磁有序性以及其磁和空间结构之间的不寻常耦合。即将进行的实验将使用磁偏转来测量团簇中的有效磁化强度，并与理论模型相结合，以了解这些粒子的磁性特征。第二个项目将研究孤立的热激发团簇在经历自发热异构化时的时间演化。这些实验将使用皮秒和飞秒激光脉冲的泵浦探测技术进行，以跟踪此类团簇的结构和能量演化。除了观察从低温类固体相到高温类液体相的转变外，这些实验还将探索经典和量子动力学在描述形状变化过程中的作用。 这两个实验都涉及尖端真空、电子、激光和光学技术，将为学术界或工业界参与这项研究的研究生做好准备。原子簇在单个原子世界和块体材料世界之间架起了一座概念桥梁。这些微小粒子由 2 到 1000 个原子组成，代表了一个中间立场，可以在其中研究原子和分子的更简单行为的整体行为的增长。随着颗粒尺寸的增加，需要探索的问题包括基本特性（例如磁性）和相变（例如熔化和冻结）。随着技术向更小的尺寸发展，对这种微型系统的清晰了解已成为一种实际需要。 该个人研究者奖支持两个解决这一中间立场的实验项目。第一个项目将探索传统磁性金属（铁、钴、镍）和更不寻常的元素（稀土、铬、铑）簇中磁性和磁性的演变。由于大部分原子都在表面，这些团簇通常具有异常的磁性，并且具有奇异的热和结构特征。即将进行的实验将测量各种团簇的磁和热特性，并寻求识别具有概念和/或技术上重要的磁特性的系统。第二个项目将研究星团的时间演化，这些星团包含足够的热能，即使在真空隔离下也能改变其形状。这些形状变化的系统既不是真正的固体，也不是真正的液体，它们让我们深入了解热环境中超小型系统的复杂性。即将进行的实验将使用超快激光脉冲来实时观察团簇形状的变化，并将寻找熟悉的熔化和冻结的经典特征以及原子尺度世界中常见的不太熟悉的量子特征。特别令人感兴趣的是微小颗粒热重新排列的惊人容易性，这一因素不可避免地缩短了许多微小技术结构的短暂寿命。这两项工作都将涉及尖端的实验技术，并将为学生提供在学术界或工业界证明有用的技能和培训。