Magnetism and Dynamics in Atomic Clusters

2到1000个原子的聚集体是研究有限系统的静态和动态特性的绝佳实验室。这些性质中最有趣的是磁序，它对结构和键合非常敏感，以及类似于体相变的交叉行为，特别是熔化和冻结相变。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随各种材料簇大小的演变，包括那些块状、铁磁性、反铁磁性和非磁性的材料。这些系统的低维数和高表面体积比有利于增强磁有序和它们的磁和空间结构之间不寻常的耦合。将要进行的实验将使用磁偏转来测量团簇中的有效磁化，并与理论模型相一致，以了解这些粒子的磁性特征。第二个项目将研究孤立的、热激发的团簇在自发热异构化过程中的时间演化。实验将使用皮秒和飞秒激光脉冲的泵浦探测技术来跟踪这些星团的结构和能量演变。除了观察在高温下从低温类固相到类液相的交叉外，这些实验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的真空、电子、激光和光学技术，并将为研究生参加学术界或工业界的研究做好准备。原子团簇在单个原子的世界和大块材料的世界之间提供了一座概念性的桥梁。这些微小的粒子由2到1000个原子组成，代表了从原子和分子的简单行为中研究整体行为增长的中间地带。随着粒径的增大，需要探索的问题包括基本性质（如磁性）和相变（如熔化和冻结）。随着技术向更小的维度推进，对这种微小系统的清晰理解正在成为一种现实的需要。该个人研究者奖支持两个解决这一中间问题的实验项目。第一个项目将在传统磁性金属（铁、钴、镍）和更不寻常的元素（稀土、铬、铑）的集群中探索磁性和磁性的演变。由于大多数原子都在其表面，这些团簇通常具有不同寻常的磁性，并具有奇特的热学和结构特征。将要进行的实验将测量各种团簇的磁性和热特性，并寻求确定在概念和/或技术上具有重要磁性特性的系统。第二个项目将研究包含足够的热能的星团的时间演化，即使在真空的隔离中也能改变它们的形状。既不是真正的固体，也不是真正的液体，这些可改变形状的系统为热环境中超小型系统的复杂性提供了洞见。即将进行的实验将使用超快激光脉冲来实时观察星团的形状变化，并将寻找熟悉的经典特征，如融化和冻结，以及不太熟悉的原子尺度世界中常见的量子特征。特别令人感兴趣的是微小粒子的热重新排列令人惊讶的容易，这是一个不可避免地缩短许多微小技术结构的短暂寿命的因素。这两项努力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都有用的技能和培训。

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.