Correlations & Competition Between the Lattice, Electrons, & Magnetism
The goal of this group is to drive a feedback loop that firmly links the understanding, prediction, optimization, and discovery of new materials such as the new Fe-As high-Tc superconductors. To achieve this ambitious goal, first principles calculations and many body theory are closely coupled with experiment. Neutron and x-ray scattering are used in complementary fashion to determine the structural, electronic, and magnetic features of complex ground states, excitations, and the driving mechanisms of phase transformations in relevant materials. In addition to the in-house theory-experiment synergy, a strength of this group is its close ties with world-class synthesis efforts in several other Projects. These ties not only provide the group with access to the highest quality samples of transformational materials that are often unavailable to other laboratories (e.g., single-crystal MgB2 and Fe-As superconductors shortly after their discoveries), they also provide an effective means for input to the synthesis itself.
Topics within this Project are:
- Novel superconductors. Ames Laboratory has demonstrated world leadership in the study of high-temperature superconductivity in iron-arsenic based compounds with an effort encompassing several Projects. This Project will investigate aspects of the strongly coupled magneto-structural transitions, phonon anomalies, and magnetic interactions in these compounds. The range of possible element substitutions in these materials make them rich for developing the feedback loop mentioned at the outset, and this will be pursued. (V. Antropov, A. Goldman, B. Harmon, R. McQueeney, J. Zarestky)
- Correlations in transition metal oxides. The goal is to understand the role that magnetism plays in the electronic conduction in complex oxides such as spin-polarized conductors and mixed valent magnets. We will study the ground states and magnetic excitations materials such as Fe3O4, (R,A)MnO3, and RBaFe2O5. Understanding and ultimately controlling this coupling could lead to the development of new materials for sensors and spintronic devices. (A. Goldman, R. McQueeney, D. Vaknin)
Complex magnetic materials: This effort will continue the projects world leadership in the study of rare-earth magnetism by integration of scattering experiments and theory. We will study magnetic materials (such as R5Ge4, R2Fe17) that couple strongly to the lattice lead to functional magnetoelastic and magnetostrictive properties. The goal is to understand the microscopic origin of their magnetic properties, and to provide feedback for guiding the synthesis of advanced and optimized functional materials (A. Goldman, R. McQueeney, J. Zarestky, B. Harmon)
Pintschovius L; Weber F; Reichardt W; Kreyssig A; Heid R; Reznik D; Stockert O; Hardil K . 2008. Phonon linewidths in YNi2B2C. Pramana-Journal of Physics. 71:687-693.
Christianson A D; Lumsden M D; Delaire O; Stone M B; Abernathy D L; McGuire M A; Sefat A S; Jin R; Sales B C; Mandrus D; Mun E D; Canfield P C; Lin J Y Y; Lucas M; Kresch M; Keith J B; Fultz B; Goremychkin E . 2008. Phonon Density of States of LaFeAsO1-xFx. Physical Review Letters. 101:157004.