THEORY OF NANOMAGNETS

技术摘要：该奖项支持许多自旋与声子相互作用的量子动力学的理论研究和教育，并主要集中在分子纳米磁铁的应用上。正在研究的新方向包括磁雪崩理论、旋转诱导磁性以及由于自旋-声子耦合而产生的长程自旋-自旋关联。改进的磁雪崩理论是出于理解分子磁体晶体中观察到的磁爆现象的需要。研究了磁焰点火和传播的机理。此外，基于传播的朗道-齐纳波的另一种理论模型，使用解析和数值方法，正在与该理论进行比较。磁爆轰是由自旋与晶格变形耦合的非线性动力学驱动的可能性正在研究中。此外，正在开发一种理论方法来解决在磁性纳米颗粒中观察量子巴奈特效应的可能性。这个理论考虑了自由粒子的磁矩与机械旋转的耦合动力学。将研究自旋与高频大振幅声波的相互作用，重点是动态自旋-旋转耦合。这项研究解决了在分子磁晶体中直接观察自旋-旋转耦合的可能性。由于弱耦合自旋与声子相互作用而产生的集体行为正在被研究，以确定相干声子在提供自旋之间的长程关联中所起的作用。这项研究将结合声子瓶颈、非辐射自旋-声子态以及自旋声子弛豫的相干放大在分子磁体中的应用进行研究。我们将研究自旋晶格驰豫与磁体大小的关系。研究生、本科生以及高中生都将积极参与这项研究。这个项目涉及国际合作。非技术总结该奖项支持理论研究和教育，旨在对纳米尺度上的磁性有一个基础的了解，并发现与纳米磁铁有关的新现象。随着材料接近纳米尺寸，除了提高对经典物理崩溃的基本科学理解外，分子磁性材料和其他纳米尺度磁性粒子预计将对广泛的技术产生积极影响。例子包括磁共振成像技术、磁记录和更新的信息技术，如自旋电子学，它寻求在新设备和量子计算中利用电子的磁性以及电子的电荷。随着宏观材料的拉伸、弯曲和扭曲，磁性粒子与邻近粒子相互作用的方式强烈影响着这些纳米粒子的性能和运行环境。解释这些相互作用的理论正在发展，同时发现了这些相互作用产生的潜在有用的影响。基于这些效应的未来可能的技术进步包括激光的声学模拟，纳米尺度的光束旋转诱导的磁效应，以及一种被称为磁爆燃的特征。磁爆燃是火焰点火和随后蔓延的磁学类比。然而，在分子磁性材料中，这一过程是可逆的，这为以一种新的方式扩大我们对燃烧的理解提供了潜力。研究生、本科生以及高中生都将积极参与这项研究。这个项目涉及国际合作。

TECHNICAL SUMMARY:This award supports theoretical research and education on quantum dynamics of many spins interacting with phonons and concentrates primarily on applications to molecular nanomagnets. New directions under investigation include theories of magnetic avalanches, rotation-induced magnetism, and the occurrence of long-range spin-spin correlations due to spin-phonon coupling. The improved theory for magnetic avalanches is motivated by the need for understanding the phenomenon of magnetic deflagration observed in crystals of molecular magnets. Mechanisms initiating ignition and subsequent propagation of the magnetic flame are investigated. In addition an alternative theoretical model, based upon a propagating Landau-Zener wave, using analytical and numerical methods is being compared to this theory. The possibility that magnetic detonation is driven by non-linear dynamics of spins coupled with lattice deformations is being investigated. In addition, a theoretical method that addresses the possibility of observing the quantum Barnett effect in magnetic nanoparticles is being developed. This theory considers the coupled dynamics of a magnetic moment of a free particle with the mechanical rotations. The Interaction of spins with high-frequency large-amplitude sound waves will be investigated with an emphasis on dynamical spin-rotation coupling. This research addresses the possible direct observation of spin-rotation coupling in crystals of molecular magnets.Collective behavior due to an ensemble of weakly coupled spins interacting with phonons is a being studied to determine the role that coherent phonons play in providing long-range correlations between the spins. This study connects with the phonon bottleneck, non-radiative spin-phonon states, and coherent amplification of spin phonon relaxation will be studied in application to molecular magnets. The dependence of the spin-lattice relaxation on the size of the magnet will be investigated.Graduate and undergraduate students, as well as high school students will be actively involved in this research. This project involves international collaborations.NON TECHNICAL SUMMARYThis award supports theoretical research and education aimed at a fudamental understanding of magnetism on the nanoscale and the discovery of new phenomena involving nanomagnets. In addition to improving fundamental scientific understanding of the breakdown of classical physics as materials approach the nanoscale size regime, molecular magnetic materials and other nanoscale magnetic particles are expected to positively impact a broad range of technologies. Examples include magnetic resonance imaging technologies, magnetic recording and more novel information technologies such as spintronics, which seeks to exploit the magnetic properties of electrons as well as their charge in new devices and quantum computing. The performance and operating environment of these nanoscale particles is strongly influenced by the way the magnetic particles interact with neighboring particles as the macroscopic material stretches, bends and distorts. Theories to account for these interactions are being developed in parallel with the discovery of potentially useful effects that arise because of these interactions. Possible future technological advances based on these effects include an acoustic analog of the laser, beam rotation induced magnetic effects at the nanoscale and a feature known as magnetic deflagration. Magnetic deflagration is the magnetism analog of the ignition and subsequent spread of flames. However in molecular-magnetic materials the process is reversible which provides the potential for expanding our understanding of combustion in a novel way.Graduate and undergraduate students, as well as high school students will be actively involved in this research. This project involves international collaborations.