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Magnetism of Site Random Model - Coexistence of Ferromagnetism and Antiferromagnetism -

站点随机模型的磁性 - 铁磁性和反铁磁性的共存 -

基本信息

批准号：
09640452
负责人：
MATSUBARA Fumitaka
金额：
$ 0.7万
依托单位：
TOHOKU UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1997
资助国家：
日本
起止时间：
1997 至 1999
项目状态：
已结题

项目摘要

1. Low Temperature Phase of Spin GlassesWe have proposed a new method for evaluating the defect energy of spin glass models on finite lattices. Using the method, we have reexamined the stability of the spin glass phase of two models, the Ising model in two dimensions and the Heisenberg model in three dimensions. For both the models, the defect energy increases with the size of the lattice, suggesting the occurrence of a finite temperature phase transition. These results disprove the previous idea that the spin glass phase is realized only in the Ising model in three dimensions.2. New Simulation AlgorithmWe have developed two simulation methods, a cluster heat bath (CHB) method and a discrete update Monte Carlo method. The former method is a hybridized one of an analytic method and a stochastic method, and very effective for studying complex systems. The latter method is one for systems with long-range interactions and used for studying the spin structure of mesoscopic systems.3. Spin Structure of Mesoscopic Ultrathin Magnetic FilmsWe have studied magnetic properties of micron- and submicron-scale ultrathin ferromagnetic films with uniaxial anisotropy using a discrete update Monte Carlo method. We have found that those films exhibits different magnetic properties depending on their lattice size. In small lattices, the films exhibit properties similar to those of a usual ferromagnet. In moderate lattices, the specific heat exhibits a double peak and the magnetization increases abruptly around the lower peak temperature. In large lattices, the magnetization does not increase but the specific heat still exhibits a double peak.

1.自旋玻璃的低温相我们提出了一种计算有限晶格上自旋玻璃模型缺陷能的新方法。利用这种方法，我们重新研究了两个模型的自旋玻璃相的稳定性，即二维的伊辛模型和三维的海森堡模型。对于这两种模型，缺陷能量随着晶格的尺寸而增加，表明发生有限温度相变。这些结果反驳了先前认为自旋玻璃相只在三维Ising模型中实现的观点.新的模拟方法我们已经开发了两种模拟方法，一个集群热浴（CHB）方法和离散更新蒙特卡罗方法。前一种方法是解析方法和随机方法的混合，对于研究复杂系统是非常有效的。后一种方法是针对具有长程相互作用的系统的方法，用于研究介观系统的自旋结构。3.介观超薄磁性薄膜的自旋结构我们用离散更新蒙特卡罗方法研究了具有单轴各向异性的微米和亚微米尺度铁磁薄膜的磁性。我们已经发现，这些薄膜表现出不同的磁性取决于它们的晶格尺寸。在小晶格中，薄膜表现出与普通铁磁体相似的性质。在中等晶格中，比热呈现双峰，磁化强度在较低的峰值温度附近突然增加。在大晶格中，磁化强度不增加，但比热仍呈现双峰。