Exotic order in frustrated magnets

研究的主要重点放在烧绿石磁体上，这是一个典型的几何挫折系统。本文在以下三个方面取得了进展：1）三角格子Heisenberg反铁磁体中的涡旋有序，2）具有铁磁第二近邻相互作用的Heisenberg烧绿石反铁磁体的有序，3）具有长程RKKY相互作用的Ising烧绿石磁体的有序。对于问题1），我们通过广泛的Monte Carlo模拟，估计了经典三角格子Heisenberg反铁磁体的关联长度和关联时间，揭示了该模型的拓扑有序态是一种伴随着大而慢的自旋涨落的特殊的“自旋凝胶”态.关于问题2），通过广泛的Monte Carlo模拟，确定了该模型表现出向特殊有序态的一级跃迁，在该有序态中， ...更多信息 自旋结构因子中出现了无公度波矢的Zed，但自旋仍有很大的波动。关于主题3），由于最近对“自旋冰”磁体有序化的兴趣，我们研究了<111>具有长程RKKY相互作用的Ising磁体的有序化，这是为了模拟金属“自旋冰”磁体如Pr_2Ir_2O_7。我们通过使用埃瓦尔德求和技术进行了广泛的蒙特卡罗模拟，以充分考虑相互作用的长程性质。取决于参数k_F。代表费米波矢，该模型已被证明表现出丰富的有序行为。特别是，我们发现实验系统对应的RKKY模型在反铁磁Curie Weiss常数下，低温时呈现“2-in 2-out”局域自旋结构，与实验一致.相比之下，该模型总是表现出热力学相变到磁性长程有序态，自旋液体的行为从来没有实现。少

Main emphasis of the research has been put on the pyrochlore magnet, a typical system showing geometrical frustration. Progress has been achieved on the following three topics, 1) vortex order in the triangular-lattice Heisenberg antiferromagnet, 2) the ordering of the Heisenberg pyrochlore antiferromagnet with the ferromagnetic second-neighbor interaction, and 3) the ordering of the Ising pyrochlore magnet with the long-range RKKY interaction. Concerning the subject 1), by means of extensive Monte Carlo simulation, we estimate the correlation length and the correlation time of the classical triangular-lattice Heisenberg antiferromagnet, revealing that the topological ordered state of the model is a peculiar "spin-gel" state which accompanies large and slow spin fluctuations. Concerning the subject 2), by means of extensive Monte Carlo simulations, it was established that the model exhibited a first-order transition into the peculiar ordered state in which a sharp Bragg peak characteri … More zed by an incommensurate wavevector appeared in the spin structure factor, yet the spin remained largely fluctuating. Concerning the subject 3), motivated by the recent interest in the ordering of "spin-ice" magnets, we have studied the ordering of the <111> Ising magnet with the long-range RKKY interaction, which is intended to model metallic "spin-ice" magnets such as Pr_2Ir_2O_7. We performed extensive Monte Carlo simulation by using the Ewald sum technique to fully take account of the long-range nature of the interaction. Depending on the parameter k_F. representing the Fermi wavevector, the model has turned out to exhibit rich ordering behaviors. In particular, we have found that the RKKY model corresponding to the experimental system takes "2-in 2-out" local spin structure at low temperatures under the antiferromagnetic Curie-Weiss constant, consistently with the experiment. By contrast, the model always exhibits a thermodynamic phase transition into the magnetic long-range ordered state, a spin-liquid-like behavior being never realized. Less