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首页> 外文会议>Conference on Noise as a Tool for Studying Materials Jun 2-4, 2003 Santa Fe, New Mexico, USA >Noise as a mesoscopic probe of the colossal magnetoresistance effect
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Noise as a mesoscopic probe of the colossal magnetoresistance effect

机译：噪声作为磁阻效应的介观探针

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摘要

Epitaxial thin films and bulk crystals of the colossal magnetoresistance (CMR) material La_(2/3)Ca_(1/3)MnO_3 (LCMO) exhibit large discrete equilibrium resistance fluctuations in the region of phase space where the magne-toresistance effects are strongest. Strongly inhomogeneous current paths allow us to observe the random telegraph signals of individual mesoscopic regions of material fluctuating between the paramagnetic-semiconductor phase and the ferromagnetic-conductor phase. Temperature and field dependences of the Boltzmann factors of individual fluctuators yield measurements of the magnetic moment and entropy differences between these phases, and of the fluctuator volumes. These measurements provide some of the first quantitative thermodynamic information about the locally-homogeneous CMR phase transition in an otherwise strongly inhomogeneous system. Careful analysis of the field- and temperature-dependences allows us to discriminate between fluctuations across the (first-order) CMR phase boundary and fluctuations of magnetic domain orientation deep in the ferromagnetic state. Similar measurements of the closely-related CMR material La_(2/3)Sr_(1/3)MnO_3 show almost no noise associated with the CMR transition, consistent with a second-order phase transition in this material.
机译：巨磁致电阻（CMR）材料La_（2/3）Ca_（1/3）MnO_3（LCMO）的外延薄膜和块状晶体在磁阻效应最强的相空间区域表现出较大的离散平衡电阻波动。极不均匀的电流路径使我们能够观察到材料的各个介观区域在顺磁半导体相与铁磁导体相之间波动的随机电报信号。各个波动器的Boltzmann因子的温度和磁场相关性可测量这些相之间的磁矩和熵差以及波动器的体积。这些测量提供了一些本来就很不均匀的系统中有关局部均匀CMR相变的第一定量热力学信息。对场和温度相关性的仔细分析使我们能够区分（一阶）CMR相界上的波动和铁磁态深处的磁畴取向的波动。密切相关的CMR材料La_（2/3）Sr_（1/3）MnO_3的相似测量结果显示，几乎没有与CMR跃迁相关的噪声，与这种材料中的二阶相变一致。

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