Magnetism and Dynamics in Atomic Clusters

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极佳实验室。其中最耐人寻味的是磁序，它对结构和成键极其敏感，以及类似于主体相变的交叉行为，特别是熔化和冻结相变。这一个人研究人员奖支持此类集群中的两个实验项目。第一个项目将探索各种材料簇中磁性和磁性随大小的演变，包括块状材料、铁磁性材料、反铁磁性材料和非磁性材料。这些体系的降维和它们的高比表面积比有利于增强磁性有序以及它们的磁性结构和空间结构之间的不寻常的耦合。将要进行的实验将使用磁偏转来测量团簇中的有效磁化，并结合理论模型来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来跟踪这些星系团的结构和能量演化。除了观察高温下从低温类固体相到类液体相的交叉，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的真空、电子、激光和光学技术，将为参加这项研究的研究生为学术界或工业界做好准备。原子团簇在单个原子世界和块状材料世界之间提供了一座概念上的桥梁。这些微小的粒子由2到1000个原子组成，是研究原子和分子较简单行为的整体行为增长的中间基础。随着颗粒尺寸的增大，需要探索的问题包括基本性质(例如磁性)和相变(例如熔化和冻结)。随着技术向着越来越小的维度发展，对这种微小系统的清晰理解正成为一种现实的需要。这一个人研究人员奖支持两个解决这一中间问题的实验项目。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)的团簇中磁性和磁性随大小的演变。由于它们的大部分原子都在它们的表面，这些星团通常具有不同寻常的磁性，并具有奇异的热和结构特征。将进行的实验将测量各种星系团的磁性和热性质，并设法确定具有概念和/或技术上重要磁性特征的系统。第二个项目将研究星系团的时间演化，这些星系团包含足够的热能，即使在真空隔离的情况下也能改变其形状。这些形状变化系统既不是真正的固体，也不是真正的液体，它们提供了对热环境中超小型系统的复杂性的洞察。将要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，并将寻找人们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，微小粒子以惊人的容易热重新排列，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。这两项努力都将涉及尖端的实验技术，并将为参与其中的学生提供技能和培训，这些技能和培训将被证明对学术界或行业都有用。

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.