Experimental and Theoretical Studies of Anisotropy of Magnetic Susceptibility and Remanence

可测量的磁各向异性是由晶粒尺度和大块岩石尺度上的一套庞大而复杂的机制和物理效应造成的。这些包括：非静水应力和磁致伸缩；晶体缺陷和微观结构及其与磁畴壁的相互作用；通过颗粒流动、塑性变形或其他机制使矿物颗粒重新定向；以及非均匀分布的铁磁粒子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，通过使用具有规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相结合；各向异性相互作用磁粒子非磁滞磁化过程的数值模型并对电子束光刻合成样品的非滞后各向异性进行了实验测定。具体来说，我们的实验包括系统地研究高温变形对方解石、费雅沸石或黑云母基体中含有磁铁矿的合成样品的磁剩余率、体磁性和磁各向异性的影响。根据我们的实验方案，我们正在研究应变之间的相互关系，磁性颗粒的重定向，磁铁矿内变形微观结构的发展，体磁性能的变化，以及磁性织物的发展（通过磁化率和剩余物的各向异性来测量）。我们也在研究，使用基本的实验和理论方法，非滞后剩磁的性质和它的各向异性，一个性质是广泛测量，但不是很好理解。我们特别关注粒子间静磁相互作用的作用。利用电子束光刻技术制造的一系列纳米磁铁矿颗粒阵列，研究了磁相互作用的影响。纳米制造过程使我们能够生产具有可控颗粒尺寸、形状、方向和颗粒间距的颗粒阵列。我们的这些研究结果有助于我们更好地理解自然变形岩石中磁性结构的意义，在变形历史和机制方面。更广泛的影响包括研究生和博士后的培训和教育，以及这项工作的潜力，使岩石变形能够通过磁各向异性来表征。

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.