Excitation Dynamics of Random Magnetic Systems

这个项目是关于自旋玻璃微观有序参数的实验研究。这个迄今为止唯一的理论概念控制着这些复杂系统的动力学。本研究的结果将与进化、蛋白质折叠、神经网络和其他在其状态安排上服从层次结构的物理现象相关。感兴趣的参数是零场冷却磁化强度的非线性磁场依赖关系。这个量将在一个温度范围内确定，从非常低的值到玻璃自旋温度Tg附近。利用研究人员开发的理论描述，Mzfc的对数对磁场的导数将产生P(q)的显式形式，即自旋玻璃的巴黎阶参数。使用其他实验“卡尺”，该研究将尝试提取控制自旋玻璃行为的层次树的分支比率。随机磁系统，特别是自旋玻璃，是自然界中发现的各种行为的可测量表征。它们的特性可以揭示人类进化、蛋白质在溶液中的行为和人类大脑的功能等不同领域。看起来，这些看似随机的结构实际上服从非常狭窄的几何形状，这是一种极大的简化。这个项目设计了一些实验，可以通过测量稀磁合金的磁性来提取潜在的几何形状。这些材料将在广泛的温度和磁场范围内进行研究，目的是提取定义其动态行为的微观参数。这不仅与这一类重要的物理系统有关，而且与各种各样的自然现象有关。＊＊＊

9623195 Orbach This project deals with the experimental study of the microscopic order-parameter of spin-glasses. This here-to- fore solely theoretical concept controls the dynamics of these complex systems. The results of this study will have relevance to the fields of evolution, protein folding, neural networks, and other physical phenomena which obey hierarchical structure in the arrangement of their states. The parameter of interest is the non-linear magnetic field dependence of the zero-field-cooled magnetization, Mzfc. This quantity will be determined over a range of temperatures, from very low values up to the vicinity of the spin-glass temperature, Tg. Using a theoretical description developed by the investigators, the derivative of the logarithm of Mzfc with respect to the magnetic field will generate an explicit form for P(q), the Parisi order- parameter for spin-glasses. Using other experimental "calipers", the study will attempt to extract the branching ratios for the hierarchical tree which governs spin-glass behavior. %%% Random magnetic systems, in particular, spin-glasses, are measurable representations of a wide variety of behavior found in nature. Their properties can shed light on such diverse fields as human evolution, the behavior of proteins in solution, and the functioning of the human brain. It appears that these seemingly random structures in fact obey very constricted geometries, an immense simplification. This project has devised experiments which should enable the extraction of the underlying geometry by measuring the magnetic properties of dilute magnetic alloys. The materials will be investigated over a wide range of temperature and magnetic field with the objective of extracting the microscopic parameters which define their dynamic behavior. This will have relevance not only to this important class of physical s ystems, but also to a wide variety of natural phenomena. ***