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

RUI：孤对化合物和磁铁矿中磁性、电荷和轨道有序性的光学研究

• 批准号: 0805073
• 负责人: Lev Gasparov
• 金额: $ 15.87万
• 依托单位: University of North Florida
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-06-01 至 2013-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0805073&HistoricalAwards=false
• 关键词: RUI; Optical; Studies; Magnetic; Charge

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.

有序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过程的好例子。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组织起来。电子“自旋”是另一种可能导致有序的电子特性。人们可以把电子自旋想象成一个由电子携带的小永磁体。磁体的磁场强度和方向称为磁矩。有时这些磁矩以一种特定的方式排列，导致磁（自旋）有序。还有一种排序与电子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（例如球形和哑铃状）。据信，在某些化合物中，轨道的取向可能导致轨道的有序。任何类型的排序都会产生化合物的新性质。例如，电荷排序我的铅的化合物具有较低的导电性。自旋和轨道排序可能导致化合物具有更强的磁体。因此，了解排序是如何发生的将会导致更好的材料工程。本项目使用光谱学来研究和理解两类材料中不同类型的有序。磁铁矿是人类已知的第一种磁性物质，自1939年发现磁铁矿以来，磁铁矿中的电荷排序物理学一直是个谜。过渡金属碲化物Co5(TeO3)4Br2, Co7(TeO3)4Br6显示出丰富的磁相图，表明复杂的磁有序和可能的轨道有序，因此是研究自旋和轨道有序的良好候选者。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获益良多。高中生将有机会在这个项目的某些方面进行工作。众所周知，相关电子系统可以显示许多不同类型的有序，从而产生丰富的相图。了解这些排序过程的复杂性质可以通过光谱学来实现。该个人研究者奖支持对电子、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化物经历了结构和磁性转变。经过60多年的研究，磁铁矿（Fe3O4）结构转变（Verwey转变）的性质仍然是一个悬而未决的问题。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。Co5(TeO3)4Br2、Co7(TeO3)4Br6是一种新型的过渡金属碲化物，具有Te4+阳离子的低维排列和自旋为3/2的Co2+离子的未填充d轨道控制的磁性能。Co7(TeO3)4Br6和Co5(TeO3)4Br2都具有丰富的磁相图，表明复杂的磁序和可能的轨道序。这些化合物的光谱测量将为相关电子系统的物理学提供关键的实验见解。在这个研究项目中工作的学生将通过在现代研究环境中工作和发展重要的解决问题的技能而受益匪浅。