Macroscopic Quantum Phenomena in Magnetic Systems

宏观自由度的量子力学隧穿 将在磁系统中进行研究，例如 反铁磁粒子中的Neel矢量 尺寸大约100安格利亚。如果存在这种情况， 扩大叠加的已知适用范围 原则将特别强调学习 由于环境自由度而引起的耗散，以期 指导和理解实验。耗散的例子 代理人是核自旋，涡流和自旋波。某些 自旋中拓扑相引起的量子现象 还将研究路径积分。磁畴壁运动 也将从隧道的角度进行研究。的组合 将采用路径积分和微扰方法， 数字和分析工作。 %%% 这个提议涉及到量子力学的理论研究 适用于具有大量自由度的系统。的 问题是其状态由 宏观上不同状态的叠加（例如，磁 其行为方式与那些 只有很少的自由度--这就是隧道穿越 经典禁止的障碍或表现出共振。好 这些现象的候选者是小的磁性粒子，但是， 到目前为止，旨在证明存在的实验已经 争议这项工作旨在指导和批判实验， 研究这些机制（能量损失）， 效果这项工作有价值，因为它可能与以下方面有关： 磁记录介质，其中这种效应是不希望的。

The quantum mechanical tunneling of macroscopic degrees of freedom will be studied in magnetic systems, such as the total moment in ferromagnetic and the Neel vector in antiferromagnetic particles of size approx. 100 Angstroms. If such exists, it would significantly enlarge the known range of applicability of the superposition principle. Special emphasis will be placed upon studying dissipation due to environmental degrees of freedom with a view to guiding and understanding experiments. Examples of dissipative agents are nuclear spins, eddy currents and spin waves. Certain quantum phenomena resulting from the topological phase in the spin path integral will also be studied. Magnetic domain wall motion will also be studied from a tunneling perspective. A combination of path integral and perturbative methods will be employed involving both numerical and analytical work. %%% This proposal involves the theoretical study of quantum mechanics applied to systems with a large number of degrees of freedom. The question is whether systems whose state is determined by a superposition of macroscopically distinct states (eg. a magnetic moment and its orientation) can behave in a similar way to those with few degrees of freedom - that is exhibit tunneling across classically forbidden barriers or exhibit resonance. Good candidates for these phenomena are small magnetic particles, but, to date, experiments aiming at proof of existence have been controversial. This work aims to guide and critique experiment and to study those mechanisms (energy loss) which could mask the effect. The work has value because of its possible relevance to magnetic recording media where such effects would be undesirable.