High Temperature Magnetic Imaging of Titanomagnetites

钛磁铁矿的高温磁成像

• 批准号: 1446998
• 负责人: Bruce Moskowitz
• 金额: $ 27万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1446998&HistoricalAwards=false
• 关键词: Temperature; Magnetic; Imaging; Titanomagnetites

Naturally occurring magnetic iron oxides in the form of microscopic mineral grains are common in trace amounts in rocks, sediments, and soils as well as in archeological and extraterrestrial materials. Through various geological processes and to varying degrees of reliability, iron-oxide particles can record and store paleomagnetic information about the direction and strength of ancient planetary fields. One such process is thermomagnetic recording, whereby magnetic minerals in igneous rocks are magnetized by cooling from high temperatures to ambient surface temperatures in the presence of the geomagnetic field. Understanding the physical mechanisms for thermomagnetic recording is essential for accurate recovery of paleomagnetic information from natural materials. Yet our theoretical understanding is predicated on the simplest internal micromagnetic configurations (single-domain), appropriate for just the smallest grain sizes, and does not cover the more abundant larger grains exhibiting complex configurations (multi-domain). This research will address thermomagnetic recording in multi-domain grains by direct observations of their micromagnetic configurations, and their changes with experimentally applied fields and controlled temperatures. The research activity will improve our ability to study the fundamental physics of magnetic behavior at elevated temperatures and will improve our understanding of the magnetic behavior of common magnetic minerals. This research will benefit geoscientists investigating the origins and evolution of planetary magnetic fields on Earth and elsewhere in the solar system.Natural recording media, from which geoscientists strive to retrieve information on the ancient history of geomagnetic field, most commonly do not hold their data in well-behaved, high-fidelity magnetic mineral grains, but rather in grains with more complex micromagnetic structures. Direct high-resolution observation of the temperature-dependent micromagnetic structures in common magnetic minerals has recently become possible with the development of high-temperature magnetic force microscopes (MFM) capable of imaging magnetic patterns up to approximately 400°C. This project will focus on a detailed MFM study of the evolution of magnetization structures in grains of natural and synthetic iron oxides as functions of temperature, applied weak fields, grain size, and prior magnetic treatments. It will allow the team to study the mechanisms of natural magnetic recording, to understand their sensitivity to thermal or chemical overprinting over geologic time, and to devise optimized laboratory methods for the recovery of paleomagnetic field data from natural recording media. The research supported here will provide insight into the micromagnetic mechanisms responsible for thermoremanent magnetization and the fundamental processes that allow estimates of the paleointensity of the ancient geomagnetic field to be determined experimentally in the laboratory.

天然存在的微小矿物颗粒形式的磁性氧化铁常见于岩石、沉积物和土壤以及考古和外星材料中，通过各种地质过程并以不同程度的可靠性记录氧化铁颗粒。并存储有关古代行星磁场方向和强度的古地磁信息，其中一种过程是热磁记录，通过在存在的情况下从高温冷却到环境表面温度，火成岩中的磁性矿物被磁化。了解热磁记录的物理机制对于从天然材料中准确恢复古地磁信息至关重要，但我们的理论理解是基于最简单的内部微磁结构（单域），仅适用于最小的颗粒尺寸。不涵盖表现出复杂结构（多域）的更丰富的较大颗粒，这项研究将通过直接观察其微磁结构来解决多域颗粒中的热磁记录问题。以及它们随实验应用场和受控温度的变化。这项研究活动将提高我们研究高温下磁性行为的基础物理的能力，并将提高我们对常见磁性矿物磁性行为的理解。这项研究将有利于地球科学家的研究。地球和太阳系其他地方行星磁场的起源和演化。地球科学家努力从中检索有关地磁场古代历史的信息的自然记录介质，通常不会以良好的、高保真度保存数据磁性矿物随着能够对磁性图案进行成像的高温磁力显微镜（MFM）的发展，对常见磁性矿物中与温度相关的微磁结构的直接高分辨率观察已成为可能。该项目将重点对天然和合成氧化铁晶粒中磁化结构随温度、施加的弱场、晶粒尺寸和先前磁性的演变进行详细的 MFM 研究。该研究将使研究小组能够研究自然磁记录的机制，了解其对地质时期热或化学叠印的敏感性，并设计优化的实验室方法来从自然记录介质中恢复古磁场数据。这里将深入了解导致热剩磁化的微磁机制以及允许在实验室中通过实验确定古代地磁场古强度估计的基本过程。

项目成果

High‐Temperature Observation of Transdomain Transitions in Vortex States in Intermediate Titanomagnetite

中钛磁铁矿涡旋态跨域跃迁的高温观测

• DOI: 10.1029/2019jb017857
• 发表时间: 2019-08
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: Khakhalova, E.;Moskowitz, B. M.
• 通讯作者: Moskowitz, B. M.