Noise and Aging in Disordered Magnetic Materials

*非技术摘要*技术进步有赖于新材料的开发，新材料的性能是为应用量身定做的。例如，在计算机中读取磁盘的设备依赖于特殊类型的材料，其电阻对磁场非常敏感。虽然有成熟的技术来分析具有简单结晶顺序的材料，但更广泛的类别的材料，这些材料没有那么好的有序，甚至看起来随机(“玻璃状”)，则更难分析。这个项目的重点是使用一种技术，即随机涨落(噪声)的研究，来观察无序的磁系统，特别是那些其电阻取决于磁性的系统。这项技术使人们能够更好地了解无序系统的哪些组件负责其对外场的响应，这反过来对改进材料设计是有用的。这个项目的主要目的之一是培养一名博士后，使其成为本实验室多年来开发的一系列噪声技术方面的专家。本科生研究人员还将有机会进行小规模、可接触的科学研究。对常见无序磁系统的各种定性描述仍未确定。最广为人知的问题是，现实中的斯普林斯们适应了什么样的状态。还有许多重要的体系(例如钴矿)，在这些体系中，自旋玻璃物理似乎与更传统的领域共存。这个项目的重点是使用噪声来研究无序的磁系统。这些系统的小样本中的非高斯噪声提供了对详细的内部状态的探测。例如，它应该允许在嵌入在自旋玻璃基质中的几乎独立的铁磁区和形成更大规模的团簇玻璃的相互作用的铁磁区之间进行区分。对自旋玻璃的小规模涨落实验提供了单个状态的指纹，这应该有助于解决几种类型的导电自旋玻璃有多少非对称性相关状态的问题。锰氧化物中的几个剩余问题，特别是是否存在被视为最好的滤镜的制度，也适用于这些小规模的噪音调查。老化调查也对玻璃关联的形式非常敏感，将与噪音工作一起使用。这个项目的主要目的之一是培养一名博士后，使其成为本实验室多年来开发的一系列噪声技术方面的专家。本科生研究人员还将有机会进行小规模、可访问的科学研究

*****NON-TECHNICAL ABSTRACT*****Technological advancement relies on the development of new materials with properties tailored to applications. For example, the devices that read the magnetic disks in computers rely on special types of material whose electrical resistance is very sensitive to magnetic fields. Although there are well-developed techniques for analyzing materials which have simple crystalline order, the broader class of materials which are not so well ordered, or which even look random ('glassy') are harder to analyze. This project focuses on the use of a technique, the study of random fluctuations ('noise'), to look at disordered magnetic systems, especially ones whose electrical resistance depends on magnetism. This technique allows one to obtain a much better picture of what components of a disordered system are responsible for its response to applied fields, and that in turn is useful for improving material design. One of the key purposes of this project is to train a postdoctoral fellow to become an expert in a collection of noise techniques developed over the years in this laboratory. Undergraduate researchers will also have an opportunity to perform small-scale, accessible science.*****TECHNICAL ABSTRACT*****A variety of qualitative characterizations of common disordered magnetic systems remain unsettled. The best known is the question of what sorts of states realistic spinglasses settle into. There are also many important systems (e.g. cobaltites) in which spinglass physics appears to coexist with domains of more conventional order. This project focuses on the use of noise to investigate disordered magnetic systems. Non-Gaussian noise in small samples of these systems provides a probe of the detailed internal states. It should allow discrimination, for example, between nearly independent ferromagnetic domains imbedded in a spinglass matrix and interacting ferromagnetic domains forming a larger-scale cluster glass. Small-scale fluctuation experiments on spinglasses provide fingerprints of individual states, which should help settle the question of how many non-symmetry-related states are available to several types of conducting spinglasses. Several remaining problems in manganites, particularly whether there are regimes best viewed as a strain-glass, are also amenable to these small-scale noise investigations. Aging investigations, also very sensitive to the form of glassy correlations, will be used in conjunction with the noise work. One of the key purposes of this project is to train a postdoctoral fellow to become an expert in a collection of noise techniques developed over the years in this laboratory. Undergraduate researchers will also have an opportunity to perform small-scale, accessible science