The 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.
Correlated 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.
Normal 0 false false false EN-US X-NONE X-NONE This project focused on physics of correlated electron materials. Such materials represent an intermediate case of solids between those that have itinerant electrons and those with localized electrons. A complete description of systems with strong electron correlations is still unknown. Correlated electron materials may have myriads of industrial applications. Recent expansion in the field of memory storage such as solid state hard drives is an example of applications that came from correlated electron system research. Several correlated electron materials were studied in this project however the main emphasis was on magnetite. This iron oxide is a commonly found mineral with the chemical formula Fe3O4. Its unconventional properties were known to mankind since antiquity. A compass made out of magnetite was used by the ancient Chinese to navigate the seas. In condensed matter physics, magnetite is considered to be the earliest compound known to manifest a metal-to-insulator transition, known as Verwey transition. At ambient pressure the Verwey transition in a pure or near-stoichiometric magnetite takes place at 123 K (-150C, -238F). The transition affects electric, magnetic and structural properties of the compound. In spite of decades of research, the mechanism of the transition remains an unsolved puzzle. Furthermore there is a wide spread in the reported experimental data taken on seemingly similar samples. This project put an emphasis on the effects of metal doping on the Verwey transition in magnetite. Doping can be described as either intentional or inadvertent introduction of impurities into the sample during crystal growth. The project employed high pressure to investigate how hydrostatic pressure ( up to 200,000 atm.) affects the Verwey transition in the magnetite samples with different level of metal doping. This systematic study has led to a conclusion that many seemingly contradictory high pressure results may come from the fact that the samples were inadvertently doped during crystal growth. Furthermore it was found that the observed doping effects are consistent with the charge ordering model of the Verwey transition. The results of the project were published in nine peer-reviewed publications and presented at a number of national and international conferences. Undergraduate students were integral part of the project. The students took part in each and every step of the research. Five out of nine publications (55%) that came from this project were coauthored by the undergraduates. In total eight undergraduate students participated in this project. From eight students employed in the project two (25%) were representatives of an underrepresented group in physics (female). Five of the students (62.5%) went on to the graduate school. In addition to research experience at UNF the funding from the project allowed for four undergraduates to conduct research at the national and international research centers such as Geophysical Laboratory in Washington DC and Aachen Technical University (RWTH) in Germany. The project was instrumental in establishing an exchange program between University of Technology of Troyes, France and UNF. All these accomplishments have improvement the research infrastructure at UNF and led to expansion of physics program at the University of North Florida (UNF).
