RUI: Quantum Micromagnetism

9978882 Chudnovsky这是一个RUI奖，以支持量子和无序系统中的微磁学理论研究。 特别是，将进行两个项目：（1）宏观量子隧道的磁化在固体。 本研究将跟进PI的建议，有两种交叉的温度从量子到热衰变的亚稳磁状态。 这项工作引起了显着的最近的活动计算交叉图不同对称性的自旋哈密顿。 在Mn-12中发现了一阶交叉的实验证据。 从隧道到热激活的交叉附近将制定出，考虑隧道前因子和耗散，通过映射到粒子问题的自旋问题，包括通过Caldeira-Leggett方法与环境的相互作用。 PI还将尝试为磁矩的Landau-Lifshitz方程开发等效的Caldeira-Leggett方法。 量子行为和热行为之间的两种交叉的研究将扩展到畴壁的量子脱钉和磁畴的量子成核问题。(2)还将继续研究高自旋分子团簇Mn-12和Fe-8中的自旋隧穿，以及单畴磁性粒子中共振自旋隧穿及其实验检测的可能性。 对于分子团簇，重点将放在热辅助共振和非共振隧穿，量子雪崩，量子相干和贝里相位振荡的可能性的理论。 最近，Wernsdorfer和Sessoli在Fe-8中报道了这种振荡。 将研究耗散对这些振荡的影响。 我们将发展连续和离散能级模型来定量地解释Mn-12和Fe-8中的量子-经典交叉图。 PI还将研究由外部磁场触发的激光对自旋能级的影响的可能性。 对于单畴粒子，问题是在具有一定尺寸分布的多粒子系统中是否可以检测到自旋能级的量子化。 考虑到能级量子化，计算了铁磁和反铁磁粒子的弛豫和阻塞温度与场的关系。这是一个RUI奖，以支持量子和无序系统中的微磁学理论研究。 具体而言，将开展两个项目：（1）将研究固体中磁化的宏观量子隧穿，（2）将研究高自旋分子团簇中的自旋隧穿和单畴磁性粒子中共振自旋隧穿的可能性。 一般来说，这项工作研究了量子效应在宏观长度尺度上表现出来的系统的物理学。

9978882ChudnovskyThis is an RUI award to support theoretical research on micromagnetism in quantum and disordered systems. In particular, two projects will be undertaken:(1) Macroscopic quantum tunneling of magnetization in solids. This research will follow up on the PI's suggestion that there are two kinds of crossover on temperature from quantum to thermal decay of a metastable magnetic state. This work has induced significant recent activity on computing crossover diagrams for spin Hamiltonians of different symmetry. Experimental evidence of the first-order crossover has been found in Mn-12. The vicinity of the crossover from tunneling to thermal activation will be worked out, with account of the tunneling prefactor and dissipation, by mapping the spin problem onto a particle problem and including the interaction with the environment via the Caldeira-Leggett method. The PI will also attempt to develop an equivalent of the Caldeira-Leggett approach for the Landau-Lifshitz equation for the magnetic moment. The study of two kinds of crossover between quantum and thermal behavior will be extended to problems of quantum depinning of domain walls and quantum nucleation of magnetic domains.(2) Research will also continue on spin tunneling in high-spin molecular clusters, Mn-12 and Fe-8, and on the possibility of resonant spin tunneling and its experimental detection in single-domain magnetic particles. For the molecular clusters, the emphasis will be on the theory of thermally assisted resonant and non-resonant tunneling, quantum avalanches, the possibility of quantum coherence and Berry-phase oscillations. Such oscillations have been recently reported by Wernsdorfer and Sessoli in Fe-8. The effect of dissipation on these oscillations will be studied. The continuous and discrete-level models will be developed to explain quantitatively the quantum-classical crossover diagrams in Mn-12 and Fe-8. The PI will also study the possibility of the laser effect on spin levels, triggered by the external magnetic field. For single domain particles the question is whether one can detect quantization of spin levels in a many-particle system with a certain size distribution. The field dependence of the relaxation and of the blocking temperature will be computed, with account of level quantization, for ferro-and antiferromagnetic particles.%%% This is an RUI award to support theoretical research on micromagnetism in quantum and disordered systems. In particular, two projects will be undertaken: (1) research will be done on macroscopic quantum tunneling of magnetization in solids, and (2) research will be done on spin tunneling in high-spin molecular clusters and on the possibility of resonant spin tunneling in single-domain magnetic particles. Generally, this work investigates the physics of systems in which quantum effects manifest themselves at the macroscopic length scales.***