Experimental Studies in High-Spin Molecular Magnets

该项目研究了含有磁性原子团的分子的磁性，这些磁性原子团被交换耦合，以产生相同的“纳米磁铁”晶格；特别是Mn12-醋酸盐和Fe8。这些材料具有许多有趣的性质：共振自旋隧穿，磁弛豫中的量子干涉(Berry相)效应，自旋的量子相干振荡，以及热辅助磁弛豫和纯量子隧道弛豫之间突然交叉的证据。尽管已经取得了很大的进展，但对这些材料的充分理解还有待于一些重要问题的解决，包括自旋-声子耦合的强度，偶极相互作用和超精细场的作用，以及热辅助量子隧道和纯量子隧道之间交叉的性质。通过使用微米尺寸的霍尔棒在非常低的温度下进行测量，该项目将研究外部施加的横向磁场的影响，微波辐射的影响，并寻找可能的铁磁或偶极有序。从基本的角度来看，分子磁体很有趣，因为它们代表了经典磁学和量子磁学之间的分界线。它们也很有趣，因为它们可能用于非常高密度的存储，并作为量子计算中元素的潜在候选者。参与该项目的研究生接受具有尖端技术的基本实验技术培训。这项培训将为他们在学术界、工业或政府的一系列职业生涯做好准备。Mn12-乙酸酯和Fe8是有机分子晶体，包含大量规则间隔的、磁性相同的自旋10团簇，其大小介于量子和经典制度之间。人们对这些材料的兴趣是由一系列引人注目的量子力学效应的实验观测引发的，包括自旋磁矩的量子隧道效应、量子力学相位干涉和量子态的叠加。尽管已经取得了很大的进展，但对这些材料的充分理解还有待于一些重要问题的解决，包括自旋磁矩与晶格振动的耦合强度，偶极相互作用和核场的作用，以及量子制度和经典制度之间交叉的性质。通过使用微米尺寸的霍尔棒在很低的温度下进行测量，我们建议研究外部横向磁场的影响，微波辐射的影响，并寻找可能的铁磁或偶极有序。除了出于基本原因的兴趣外，这些材料还很重要，因为它们可能用于非常高密度的存储，并作为量子计算中元素的潜在候选者。参与该项目的研究生接受具有尖端技术的基本实验技术培训。这项培训将为他们在学术界、行业或政府的一系列职业生涯做好准备。

This project investigates the magnetic properties of molecules containing clusters of magnetic atoms that are exchange coupled to produce a lattice of identical "nanomagnets; in particular, Mn12-Acetate and Fe8. These materials have a number of interesting properties: resonant spin tunneling, quantum interference (Berry's phase) effects in the magnetic relaxation, quantum coherent oscillations of the spin, and evidence for an abrupt crossover between thermally assisted magnetic relaxation and relaxation by pure quantum tunneling. Although much progress has been made, a full understanding of these materials awaits the resolution of a number of important issues, including the strength of spin-phonon coupling, the roles of dipolar interactions and hyperfine fields, and the nature of the crossover between thermally-assisted and pure quantum tunneling. Through measurements at very low temperatures using micron size Hall bars, this project will study the effect of externally applied transverse magnetic fields, the effect of microwave radiation, and to search for possible ferromagnetic or dipolar ordering. Molecular magnets are interesting from a fundamental point of view because they represent the borderline between classical and quantum magnetism. They are also interesting for their possible use for very high-density storage, and as potential candidates for elements in quantum computation. Graduate students involved in the project receive training in fundamental experimental techniques with cutting edge technology. This training will prepare them for a range of careers in academe, industry or government.Mn12-acetate and Fe8 are organic molecular crystals containing a very large number of regularly spaced, magnetically identical spin-10 clusters of a size that is borderline between the quantum and classical regimes. Interest in these materials has been sparked by a remarkable series of experimental observations of quantum-mechanical effects, including quantum tunneling of the spin magnetic moment, quantum-mechanical phase interference and the superposition of quantum states. Although much progress has been made, a full understanding of these materials awaits the resolution of a number of important issues, including the strength of the coupling of the spin magnetic moment to lattice vibrations, the roles of dipolar interactions and nuclear fields, and the nature of the crossover between the quantum and classical regimes. Through measurements at very low temperatures using micron size Hall bars, we propose to investigate the effect of externally applied transverse magnetic fields, the effect of microwave radiation, and to search for possible ferromagnetic or dipolar ordering. In addition to their interest for fundamental reasons, these materials are important for their possible use in very high-density storage, and as potential candidates for elements in quantum computation. Graduate students involved in the project receive training in fundamental experimental techniques with cutting edge technology. This training will prepare them for a range of careers in academe, industry or government.