Experimental and Theoretical Studies of Anisotropy of Magnetic Susceptibility and Remanence

可测量的磁各向异性是由一套大而复杂的机制和物理效应在颗粒尺度和整体岩石尺度上产生的。这些包括：非静力应力和磁致伸缩；晶体缺陷和微结构及其与磁畴壁的相互作用；颗粒流动、塑性变形或其他机制引起的矿物颗粒的重新取向；以及非均匀分布的亚铁磁性颗粒之间的静磁相互作用。在我们的研究中，我们针对这一复杂过程的特定方面，通过组合使用具有指定成分和颗粒特征的合成岩石类似物的受控高温变形实验、各向异性相互作用的磁性颗粒的无滞后磁化过程的数值模型，以及通过电子束光刻产生的合成样品的无滞后各向异性的实验确定。具体来说，我们的实验涉及到系统地研究高温变形对合成样品的剩磁、体磁性质和磁各向异性的影响。合成样品中含有方解石、铁沸石或黑云母基质中的磁铁矿。根据我们的实验方案，我们正在研究应变、磁性颗粒的重取向、磁铁矿内部变形微结构的发展、体磁性质的变化以及通过磁化率和剩磁的各向异性来测量的磁组构的发展之间的相互关系。我们还在使用基本的实验和理论方法来研究无滞后剩余磁化的性质及其各向异性，这一特性得到了广泛的测量，但还没有被很好地理解。我们特别关注粒子间静磁相互作用的作用。人们正在利用电子束光刻产生的一系列磁性颗粒纳米碎块阵列来研究磁相互作用的影响。纳米制造工艺使我们能够制造出颗粒大小、形状、取向和颗粒间距可控的颗粒阵列。这些研究的结果有助于我们更好地理解自然变形岩石中磁性组构在变形历史和机制方面的重要性。更广泛的影响包括对研究生和博士后的培训和教育，以及这项工作允许岩石变形以磁各向异性为特征的潜力。

Measurable magnetic anisotropy results from a large and complex set of mechanisms and physical effects on both the grain scale and the bulk rock scale. These include: nonhydrostatic stress and magnetostriction; crystal defects and microstructures and their interactions with magnetic domain walls; reorientation of mineral grains by particulate flow, plastic deformation or other mechanisms; and magnetostatic interactions among nonuniformly-distributed ferrimagnetic particles. In our research, we are targeting particular aspects of this complex set of processes, through a combination of controlled high-temperature deformation experiments using synthetic rock analogs with prescribed compositions and particle characteristics; numerical models of the anhysteretic magnetization process for anisotropically-interacting magnetic particles; and experimental determination of the anhysteretic anisotropy of synthetic samples produced by electron-beam lithography. Specifically our experiments involve the systematic investigation into the effects of high-temperature deformation on magnetic remanence, bulk magnetic properties and magnetic anisotropy in synthetic samples containing magnetite in a matrix of calcite, fayalite, or biotite. With our experimental protocols, we are studying the interrelationships between strain, reorientation of magnetic grains, development of deformation microstructures within the magnetites, changes in bulk magnetic properties, and development of magnetic fabrics as measured by anisotropy of magnetic susceptibility and remanence. We are also investigating, using fundamental experimental and theoretical approaches, the nature of anhysteretic remanent magnetization and its anisotropy, a property that is widely measured but not very well understood. We are especially focusing on the role of interparticle magnetostatic interactions. The effects of magnetic interactions are being studied using a series of nanofabricated arrays of magnetite particles produced by electron beam lithography. The nanofabrication process allows us to produce particle arrays with controlled particle sizes, shapes, orientations and interparticle spacings. Our results of these investigations are helping us better understand the significance of magnetic fabrics in naturally-deformed rocks, in terms of deformation history and mechanisms. Broader impacts include the training and education of a graduate student and a postdoc, and the potential of this work to allow rock deformation to be characterized by magnetic anisotropy.