Magnetic, Electronic and Structural Transitions in Iron Bearing Minerals under Pressure: Theory and Experiment

含铁矿物在地球科学和技术中都具有重要的作用。例如，磁铁矿-尖晶石固溶体系列的物种是地壳剩余磁化的主要载体。此外，氢氧化铁可作为研究含铁矿物在地壳和地幔条件下的作用的模式体系。本项目的目标是通过最先进的密度泛函理论(DFT)计算和实验技术相结合的方法来研究极端条件下含铁矿物的结构-性质关系。我们特别关注结构相变和磁性相变之间的相互作用，电子性质的可能变化(例如，金属到绝缘体的转变)以及自旋交叉现象。选取了三个研究对象。1)最近提出的磁铁矿中压力诱导的尖晶石反转到正常尖晶石转变。2)钛磁铁矿在压力下的磁性能随钛浓度的变化。3)轻元素在铁(氧)氢氧化物的压力诱导相变和可能的自旋交叉中的作用。为了解决这些问题，我们将使用第一性原理方法，考虑到带理论以外的电子关联，以及实验程序，这些程序旨在弥合固体物理学中使用的方法，特别是穆斯堡尔方法和衍射法与地球物理学中应用的方法之间的差距，在地球物理学中，理解剩磁的起源是至关重要的。

Iron bearing minerals play an important role in both geosciences and technology. For example, species of the magnetite-ülvospinel solid solution series are the principle carriers of remanent magnetization in the Earth’s crust. Moreover, the iron oxyhydroxides can be regarded as a model system to explore the effect of hydrous Fe-bearing minerals at conditions of the Earth’s crust and mantle. The goal of our project is to investigate the structure-property relation in iron bearing minerals at extreme conditions by combining state of the art density functional theory (DFT) calculations with experimental techniques. In particular we focus on the interplay between structural and magnetic phase transitions, possible changes in electronic properties (e.g. metal-to-insulator transitions) as well as spin-crossover phenomena. Three study targets are selected. 1) The recently proposed pressure-induced inverse-to-normal spinel transition in magnetite. 2) The variation of magnetic properties of titanomagnetite under pressure as a function of titanium concentration. 3) The role of light elements in pressure-induced phase transitions and possible spin-crossover in iron (oxy)hydroxides. To address these issues we will employ first principles methods taking into account electronic correlations beyond band theory, as well as experimental procedures that are designed to bridge the gap between approaches used in the solid-state physics community, notably Mössbauer and diffraction methods, with those applied in geophysics, where understanding the origin of magnetic remanence is of prime importance.