CMG COLLABORATIVE RESEARCH: Magnetic Viscosity and Thermoremanent Magnetization in Interacting Single-domain Ferromagnets

CMG 合作研究：相互作用单畴铁磁体中的磁粘度和热剩磁化

• 批准号: 1025564
• 负责人: Daniel Bates
• 金额: $ 14.54万
• 依托单位: Colorado State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-15 至 2014-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1025564&HistoricalAwards=false
• 关键词: CMG; COLLABORATIVE; RESEARCH; Magnetic; Viscosity

Many major hypotheses about the geology of pre-Mesozoic eras rely critically on paleomagnetic data. Magnetic remanence in rocks records the ancient magnetic field and provides information on plate tectonics and the history of the geodynamo. For the remanence to be useful, it must remain stable as the rocks are subjected to temperature increases, pressure, and changes in the chemical environment. Suitable rocks become increasingly rare as their age increases. In pre-Mesozoic rocks, many of the most promising magnetic recorders do not fit the standard model for good paleomagnetic recorders because the magnetic minerals interact with each other through magnetic fields. If these interactions are not properly accounted for, paleomagnetic measurements can be misleading. The effect of interactions is complicated by thermal relaxation of the magnetic moments in which the magnetization jumps over energy barriers between stable states. The greatest challenge facing models of interacting magnets is to find these energy barriers. The object of this proposal is to harness some powerful methods from numerical algebraic geometry to calculate the magnetic effects of particle interactions and thermal fluctuations. The equilibrium equations for interacting magnets can be expressed as systems of polynomial equations. Methods will be developed to find all the stable states and transition states for such systems using homotopy continuation. The time dependence of the magnetization can then be expressed as a set of kinetic equations. There will be three main applications of this theory:1. A theory of remanence acquisition and demagnetization for titanomagnetite inclusions in sub-aerial basalts and Precambrian shields. These titanomagnetites are often networks of strongly interacting magnetite grains separated by ilmenite lamellae. The effect of particle interactions and grain growth on the accuracy of paleointensity measurements will be determined.2. A model of isothermal hysteresis measurements of sedimentary systems involving single-domain and superparamagnetic particles that may have significant interactions. These include remagnetized carbonates, sediments with fossil magnetotactic bacteria, and sediments with greigite or pyrrhotite. Such systems can carry important information on ancient environments and human impacts.3. A model of measurements involving oscillating fields, including anhysteretic remanent magnetization (ARM) and alternating field demagnetization of remanence. These measurements are common tools in paleomagnetic analysis.

关于前中生代地质学的许多主要假设都严重依赖于古地磁数据。岩石中的剩磁记录了古代磁场，并提供了有关板块构造和地球发电机历史的信息。为了使剩磁发挥作用，当岩石受到温度升高、压力和化学环境变化时，剩磁必须保持稳定。随着年龄的增加，合适的岩石变得越来越稀有。在前中生代岩石中，许多最有前途的磁记录仪并不符合良好古磁记录仪的标准模型，因为磁性矿物通过磁场相互作用。如果没有正确考虑这些相互作用，古地磁测量可能会产生误导。磁矩的热弛豫使相互作用的影响变得复杂，其中磁化强度跨越稳定状态之间的能垒。相互作用磁体模型面临的最大挑战是找到这些能量势垒。该提案的目的是利用数值代数几何中的一些强大方法来计算粒子相互作用和热波动的磁效应。相互作用的磁体的平衡方程可以表示为多项式方程组。将开发方法来使用同伦延拓找到此类系统的所有稳定状态和过渡状态。磁化强度的时间依赖性可以表示为一组动力学方程。该理论将有三个主要应用： 1．地下玄武岩和前寒武纪地盾中钛磁铁矿包裹体的剩磁获取和退磁理论。这些钛磁铁矿通常是由钛铁矿片层分隔开的强相互作用的磁铁矿颗粒网络。将确定颗粒相互作用和颗粒生长对古强度测量精度的影响。2．沉积系统的等温磁滞测量模型，涉及可能具有显着相互作用的单域和超顺磁性颗粒。这些包括再磁化的碳酸盐、含有趋磁细菌化石的沉积物以及含有镁黄铁矿或磁黄铁矿的沉积物。这些系统可以携带有关古代环境和人类影响的重要信息。3．涉及振荡场的测量模型，包括非磁滞剩磁 (ARM) 和剩磁交变场退磁。这些测量是古地磁分析中的常用工具。