Dynamics of Disordered Non-equilibrium Systems: Hysteresis, Noise, and Domain Wall Dynamics in Systems Ranging from Magnets to Earthquakes

无序非平衡系统的动力学：从磁铁到地震的系统中的磁滞、噪声和畴壁动力学

• 批准号: 0072783
• 负责人: Karin Dahmen
• 金额: $ 15.6万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-06-01 至 2003-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0072783&HistoricalAwards=false
• 关键词: Dynamics; Disordered; Non; equilibrium; Systems

0072783DahmenThis grant supports theoretical research in condensed matter and materials physics. An increased interest in real materials has brought much attention to disordered systems. Disorder changes the free-energy landscape of a system and can lead to large energy barriers between metastable states, resulting in extremely slow approaches to equilibrium, as seen in many experiments. There has been much progress made recently in the study of distinctly nonequilibrium effects, such as collective response to an external driving force (avalanches) and internal history dependence of the system (hysteresis). This project deals with different effects of disorder on long length-scale behavior in hysteretic systems.On long length-scales, where local fluctuations in the amount of disorder are averaged out, systems driven far from equilibrium can often be usefully described by simple laws, and universal, i.e., detail independent, critical behavior has been detected. Examples range from collective dynamics of advancing domain walls in magnetic tapes to event size distributions of earthquakes. The methods applied include ideas from dynamical systems and chaos, critical phenomena, hydrodynamics and disordered systems theory.Hysteresis loops are often seen in experiments at first-order phase transformations when the systems goes out of equilibrium. They may have a macroscopic jump, roughly as seen in the supercooling of liquids, or they may be smoothly varying, as seen in most magnets. In a recent collaboration with the Sethna group at Cornell, we have studied the non-equilibrium zero-temperature random-field Ising model as a model for hysteretic behavior at first-order transformations. As disorder is added, one finds a transition where the jump in the magnetization (corresponding to an infinite avalanche) decreases to zero. At this transition, the model exhibits power law distributions of noise (avalanches), universal behavior and a diverging length-scale. The effect of adding temperature fluctuations and finite field sweep rate to the system will be studied. Tuning the sweep frequency allows the entire experimetally relevant crossover regime to be studied between the two extreme cases that are found in the literature (far from and close to equilibrium). The results will be used to interpret experiments in magnetic systems and to pursue related questions relevant to industrial applications.%%%This grant supports theoretical research in condensed matter and materials physics. An increased interest in real materials has brought much attention to disordered systems. Disorder changes the free-energy landscape of a system and can lead to large energy barriers between metastable states, resulting in extremely slow approaches to equilibrium, as seen in many experiments. There has been much progress made recently in the study of distinctly nonequilibrium effects, such as collective response to an external driving force (avalanches) and internal history dependence of the system (hysteresis). This project deals with different effects of disorder on long length-scale behavior in hysteretic systems such as magnets.***

0072783Dahmen该基金支持凝聚态和材料物理学的理论研究。 人们对真实的材料的兴趣日益增加，使得人们对无序系统给予了极大的关注。 无序改变了系统的自由能景观，并可能导致亚稳态之间的巨大能量障碍，导致非常缓慢的平衡方法，如许多实验所示。 近年来，对系统中明显的非平衡效应，如对外部驱动力的集体响应（雪崩）和系统的内部历史依赖性（滞后）的研究取得了很大进展。 本项目研究无序对滞回系统中长尺度行为的不同影响。在长尺度上，无序量的局部波动被平均，远离平衡的系统通常可以用简单的定律来描述，并且具有普遍性，即，已检测到与细节无关的关键行为。 例子从磁带中前进磁畴壁的集体动力学到地震的事件大小分布。 应用的方法包括动力学系统和混沌，临界现象，流体力学和无序系统理论的思想。滞后环经常出现在实验中的一阶相变时，系统失去平衡。 它们可能具有宏观跳跃，大致如在液体的过冷中所见，或者它们可能是平滑变化的，如在大多数磁体中所见。 在最近与康奈尔大学的Sethna小组的合作中，我们研究了非平衡零温度无规场伊辛模型作为一阶变换滞后行为的模型。 随着无序的增加，人们发现了一个转变，其中磁化强度的跳跃（对应于无限雪崩）减少到零。 在这个过渡，该模型表现出幂律分布的噪声（雪崩），普遍的行为和发散的长度尺度。 将研究在系统中加入温度波动和有限场扫描速率的影响。 调谐扫描频率允许在文献中发现的两种极端情况（远离和接近平衡）之间研究整个实验相关的交叉机制。 结果将用于解释磁性系统的实验，并探讨与工业应用相关的问题。该补助金支持凝聚态和材料物理学的理论研究。 人们对真实的材料的兴趣日益增加，使得人们对无序系统给予了极大的关注。 无序改变了系统的自由能景观，并可能导致亚稳态之间的巨大能量障碍，导致非常缓慢的平衡方法，如许多实验所示。 近年来，对系统中明显的非平衡效应，如对外部驱动力的集体响应（雪崩）和系统的内部历史依赖性（滞后）的研究取得了很大进展。 这个项目涉及在滞后系统（如磁铁）中无序对长尺度行为的不同影响。*