RUI: Optical Studies Of Magnetic, Charge And Orbital Ordering In Lone-Pair Compounds And Magnetite

非技术性质有序概念是物理学中的一个重要概念。电荷、磁性和轨道有序是材料中可能发生的有序化过程的很好的例子。其基本思想是，当条件合适时，化合物中的电荷会以某种方式自我组织起来。电子“自旋”是另一种可能导致有序化的电子性质。人们可以把电子自旋想象成一个由电子携带的小永磁体。这种磁铁的磁场强度和取向称为其磁矩。有时，这些磁矩以特定的方式排序，从而导致磁(自旋)排序。还有一种有序与电子围绕原子核运行的方式有关。有不同类型的电子“轨道”可以通过它们的形状来区分(例如，球形和哑铃形)。有人认为，在某些化合物中，轨道的取向可能导致轨道有序化。任何类型的有序都会导致化合物的新性质。例如，将我的铅带入导电性较低的化合物中。自旋和轨道有序可能会导致化合物成为更强的磁体。因此，了解有序是如何发生的，将带来更好的材料工程。这个项目使用光学光谱学来研究和理解两种材料中不同类型的有序性。磁铁矿是人类已知的第一种磁性材料，自1939年被发现以来，磁铁矿中电荷有序的物理问题一直是一个谜。过渡金属碲盐卤化物CO5(TeO3)4Br2，CO7(TeO3)4Br6显示出丰富的磁相图，表明了复杂的磁性和可能的轨道有序性，因此是研究自旋和轨道有序性的很好的候选者。学生们将积极参与这个项目，并从最先进的设备和与一些国家领先的科学实验室的合作中受益匪浅。高中生将有机会在这个项目的某些方面工作。技术摘要已知相关的电子系统显示多种不同类型的有序化，从而产生丰富的相图。了解这些有序过程的复杂性质可以通过光学光谱学来实现。这一个人研究人员奖支持对电子、轨道、自旋和晶格激发的演化进行系统的红外和拉曼光谱研究，因为磁铁矿和孤对过渡金属碲酸盐卤化物经历了结构和磁性转变。经过60多年的研究，磁铁矿(Fe3O4)的结构转变(Verwey转变)的性质仍然是一个悬而未决的问题。大量具有不同Verwey转变温度的磁铁矿样品为该化合物的系统研究提供了基础。单对过渡金属碲卤化物Co5(TeO3)4Br2，Co7(TeO3)4Br6是一种新型的材料，具有Te4+离子的低维排列和由自旋为3/2的Co2+离子的未填充d轨道控制的磁性。CO7(TeO3)4Br6和CO5(TeO3)4Br2都具有丰富的磁相图，表明了复杂的磁性和可能的轨道有序性。这些化合物的光谱测量将为相关电子系统的物理提供关键的实验洞察力。受雇于该研究项目的学生将从在现代研究环境中工作和发展重要的解决问题的技能中受益匪浅。

NON-TECHNICAL ABSTRACTThe idea of ordering is an important one in physics. Charge, magnetic and orbital order are good examples of the ordering processes that may take place in materials. The basic idea is that when conditions are right the electric charge in a compound will organize itself in a certain fashion. The electron "spin" is another electronic property that may result in ordering. One can think of an electron spin as a small permanent magnet carried by an electron. The magnetic strength and orientation of this magnet is called its magnetic moment. Sometimes these magnetic moments order in a particular fashion resulting in magnetic (spin) ordering. Yet another type of ordering is associated with the way electrons orbit the nucleus of the atom. There are different types of electron "orbitals" that can be distinguished by their shapes (spherical versus dumbbell like for example). It is believed that in some compounds orientation of the orbitals may result in orbital ordering. Any type of ordering results in new properties of the compound. For instance charge ordering my lead to a compound with less electrical conductivity. Spin and orbital ordering may result in a compound that is a stronger magnet. Understanding how ordering happens therefore will lead to better materials engineering. This project uses optical spectroscopy to study and understand different types of ordering in two types of materials. Magnetite is the first magnetic material known to mankind and the physics of charge ordering in magnetite has been a puzzle since its discovery in 1939. Transition metal tellurite halides Co5(TeO3)4Br2, Co7(TeO3)4Br6 display a rich magnetic phase diagram indicating intricate magnetic and possibly orbital ordering and therefore are good candidates to study spin and orbital ordering. Students will be actively involved in this project and benefit significantly from the state-of-the-art equipment and from the collaboration with some of the nation's leading scientific laboratories. High school students will have a chance to work on some aspects of this project. TECHNICAL ABSTRACTCorrelated electron systems are known to display a number of different types of ordering resulting in a rich phase diagram. Understanding the complex nature of these ordering processes can be achieved by optical spectroscopy. This individual investigator award supports a systematic infrared and Raman spectroscopic study of the evolution of the electronic, orbital, spin and lattice excitations as the magnetite, and lone-pair transition metal tellurite halides, undergo structural and magnetic transitions. After more than six decades of research the nature of the structural transition (Verwey transition) in magnetite (Fe3O4) is still an open question. A number of magnetite samples with different Verwey transition temperature provide a basis for systematic studies of this compound. Lone-pair transition metal tellurite halides Co5(TeO3)4Br2, Co7(TeO3)4Br6 are novel materials with low dimensional arrangement of the Te4+ cations and magnetic properties controlled by the unfilled d-orbitals of the Co2+ ion with the spin 3/2. Both Co7(TeO3)4Br6 and Co5(TeO3)4Br2 possess a rich magnetic phase diagram indicating intricate magnetic and possibly orbital ordering. Spectroscopic measurements in these compounds will provide a critical experimental insight into the physics of correlated electron systems. The students employed in this research program will benefit significantly by working in a modern research environment and by developing vital problem-solving skills.