Micromagnetic Experiments on Small Single Particles: Defects, Nucleation, and Wall-Pinning

小单颗粒的微磁实验：缺陷、成核和壁钉扎

• 批准号: 0125993
• 负责人: Susan Halgedahl
• 金额: $ 19.57万
• 依托单位: University of Utah
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-01-01 至 2006-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0125993&HistoricalAwards=false
• 关键词: Micromagnetic; Experiments; Small; Single; Particles

HalgedahlEAR-0125993The physical origins of pseudosingle-domain (PSD) behavior in small magnetic particles have been subjects of lively debate, because PSD grains are thought to carry much of the stable remanence in rocks. Two ingredients contribute most to PSD behavior: transitions in magnetic domain state and defects that pin domain walls. Despite the important role of defects having been recognized for decades, recent theories and experiments in rock magnetism underscore how little we understand about their impact on key problems such as domain wall nucleation, wall-pinning, the stabilities of remanences to alternating field (AF) demagnetization, acquisition of thermal remanent magnetization (TRM), and even the potential for extracting paleointensities from PSD grains of certain magnetic minerals. Single particles of judiciously-chosen magnetic minerals can provide "magnified" views of both nucleation events and wall-defect interactions. Owing mainly to its weak demagnetizing field and few domains, hematite is such a magnifier. This combination of properties opens up a window for studying the intrinsic impact of defects on magnetic behavior. We will use large, single platelets of hematite to better understand how defects control nucleation and domain wall pinning. Six sets of core experiments are proposed here. These would determine: (1) the thermal stability of SD-like (or near SD-like) states induced at room temperature; (2) domain states for weak-field TRM; (3) temperature dependences of nucleation fields; (4) temperature dependences of critical fields that unpin mature domain walls; (5) AF stabilities of truly multidomain hematite carrying strong-field remanence and weak-field anhysteretic magnetization, and (6) the frequency distribution of critical unpinning fields.

小磁性颗粒中伪单畴（PSD）行为的物理起源一直是激烈争论的主题，因为PSD颗粒被认为携带了岩石中大部分的稳定剩磁。两种成分对PSD行为贡献最大：磁畴状态的转变和钉扎畴壁的缺陷。尽管几十年来人们已经认识到缺陷的重要作用，但最近的岩石磁学理论和实验强调，我们对它们对诸如畴壁成核、壁钉扎、剩磁对交变场（AF）退磁的稳定性、热剩磁磁化（TRM）的获得、以及从某些磁性矿物的PSD颗粒中提取古强度的潜力。明智地选择磁性矿物的单个颗粒可以提供成核事件和壁缺陷相互作用的“放大”视图。赤铁矿的弱退磁场和畴数少是其主要原因。这种特性的组合为研究缺陷对磁性行为的内在影响打开了一扇窗。我们将使用大，单血小板的赤铁矿，以更好地了解如何控制成核和畴壁钉扎缺陷。本文提出了六组岩心实验方案。这将决定：（1）类SD的热稳定性（2）弱场TRM下的畴态;（3）成核场的温度依赖性;（4）使成熟畴壁松开的临界场的温度依赖性;（5）具有强场剩磁和弱场无磁滞磁化的真多畴赤铁矿的AF稳定性，（6）临界解钉扎场的频率分布。