Study on mechanism and dynamical control of quantum dynamics of magnets

我们研究了量子磁体的特性。特别是，我们研究了非零磁化的系统相比，已被广泛研究的单重对组成的系统。我们还研究了系统在含时场下的动力学性质。作为具体的研究对象，我们研究了S=1系统和量子化声子系统中的Spin-Peierls跃迁。我们还研究了S=1/2XY类海森堡反铁磁模型磁化过程中的量子涨落效应，发现了各种场诱导相。由于自旋交叉的相变进行了研究。本文发展了研究相互作用自旋体系ESR谱线形状的数值方法，并研究了正交二聚体体系ESR谱线形状随场方向的变化。我们还研究了纳米尺度磁体中磁化强度绝热变化的起源，发现Dzyaloshinskiii-Moriya相互作用起着重要的作用，但它会引起强烈的场方向依赖性。作为场向自由绝热跃迁的机制，我们还研究了超精细相互作用的影响。量子开关的概念已经提出。还研究了自旋涨落引起的热传导。

We have studied characteristics of quantum magnets. In particular we have studied systems with non-zero magnetization in contrast to the systems consist of the singlet pairs which have been studied widely. We also studied dynamical properties of the systems under time dependent field. As concrete subjects, we studied Spin-Peierls transition in the systems with S=1 or in the quantized phonon systems. We also studied effects of quantum fluctuation in the magnetization process of S=1/2 XY-like Heisenberg antiferromagnetic models where we found various field induced phases. Phase transitions due to the spin-crossover has been studied. We have developed numerical method to study ESR line shape of interaction spin system and studied field-direction dependence of the line shape of an orthogonal-dimer system. We also studied origin of the adiabatic change of magnetization in naoscale magnets and found the Dzyaloshinskii-Moriya interaction plays an important role, but it causes strong field-direction dependence. As a mechanism of field-direction free adiabatic transition we also studied effects of hyperfine interaction. The idea of quantum switching has been proposed. Heat conduction due to spin fluctuation has been also studied.