Magnetic Hysteresis in Magnetite: Are Synthetic Samples Stressed?

岩石磁性的测量可以提供磁性矿物性质的信息，这些信息反映环境变化并影响古强度方法的可靠性。最近的技术使我们能够快速测量磁滞，并使用现象学模型（如Preisach或FORC图）来表示磁滞的全部复杂性。为了解释这些图，我们需要一个好的磁性粒子物理模型。在这个建议的目标是开发一个定量模型的滞后在一些很好的表征合成磁铁矿样品，并严格测试它使用滞后测量在几个温度下结合详细的粒度分布。最近的微磁模型的磁滞的尺寸依赖性比以前的模型更接近，但他们的预测仍然有些低。研究人员将检验这样的假设：即使在最小的颗粒中，应力各向异性也对滞后有重要影响。将使用数值微磁模型来计算磁滞。由于磁性强烈依赖于合成方法，PI将集中在两组样品，水沉淀物和玻璃陶瓷，尺寸低于0.4微米。这些样本已经被深入研究，足够小，可以进行精确的微磁建模，并且是自然系统的模拟物。这项工作应该要么产生一个现实的模型的磁性或消除一些模型的考虑。一个成功的模型可以用来解释Preisach和FORC图。它也将是今后关于其他磁现象，如热释电磁化的工作的基础。

NewellEAR-0208446Measurements of the magnetic properties of rocks can provide information on properties of magnetic minerals that reflect environmental changes and affect the reliability of paleointensity methods. Recent technology allows us to measure magnetic hysteresis rapidly and represent the full complexity of it using phenomenological models such as Preisach or FORC diagrams. To interpret these diagrams, we need a good physical model for the magnetic particles. The goals in this proposal are to develop a quantitative model for hysteresis in some well characterized synthetic magnetite samples, and to test it rigorously using hysteresis measurements at several temperatures combined with detailed particle size distributions. Recent micromagnetic models for the size dependence of hysteresis are much closer than previous models, but their predictions are still somewhat low. The investigator will test the hypothesis that stress anisotropy has an important effect on hysteresis even in the smallest particles. A numerical micromagnetic model will be used to calculate the magnetic hysteresis. Because magnetic properties depend strongly on the method of synthesis, the PI will concentrate on two sets of samples, aqueous precipitates and glass ceramics, with sizes below 0.4 microns. These samples have been intensively studied, are small enough for accurate micromagnetic modeling, and are analogues of natural systems. This work should either produce a realistic model for the magnetic properties or eliminate some models from consideration. A successful model could be used to interpret Preisach and FORC diagrams. It would also be the basis for future work on other magnetic phenomena such as thermoremanent magnetization.