****NON-TECHNICAL ABSTRACT**** Superconductors, materials which conduct electricity without any loss due to resistance, have the potential to revolutionize the energy demands of our society in the future. However, scientists need to increase the working temperatures of the superconductors in order for them to be useful. Despite much study, in many instances the mechanism behind the superconducting behavior remains a mystery. In an attempt to develop a better understanding of their complex behaviors, this award supports a project aiming to synthesize and characterize molecular materials that mimic the magnetic properties of oxide and pnictide superconductors, two classes of superconductors that may work at higher temperatures. The challenge in directly studying such systems lies in the large magnetic interactions that exist between the magnetic sites they contained. Through a variety of chemical methods, attempts will be made to reduce the scale of these interactions by controlling the molecular assembly of model compounds using particular combinations of chemical bonds. This structural control will enable a systematic approach to vary distances between atoms, the number of magnetically-active electrons, and other properties of the material. The application of pressure may lead to other unusual discoveries. The materials discovery effort will be complemented by extensive characterization and theoretical work. The highly collaborative nature of this project makes use of several national and international user facilities and will provide unique opportunities for the undergraduate students to travel to facilities to participate in the experiments, as well as to attend professional conferences. Undergraduate student involvement in every aspect of the project will stimulate the students? growth and enthusiasm as young scientists, as well as provide them with the necessary background to begin graduate work in the future or to go on to careers in the physical sciences. This research project receives support from the Division of Materials Research and the Chemistry Division.

Technical Abstract

This award to a Predominately Undergraduate Institution will support research focusing on the design, synthesis, and characterization of low-dimensional (1- and 2D) quantum magnets, in particular square lattices, as they may mimic the structural and magnetic properties of analogous cuprate and iron-pnictide superconductors. Using specific combinations of coordinate covalent bonds and strong hydrogen bonds, the molecular positioning of components will be controlled and tuned and the magnitude/sign of the intralayer (J) and interlayer (J') magnetic interactions and their relative ratio (J'/J) will be systematically varied. The magnetic tunability of the systems will be achieved by: (a) ion-exchange (either positive or negative), (b) chemical doping, (c) application of hydrostatic or chemical pressure (i.e., isotopic substitution) and (d) co-ligand variation. Control of inter- and intralayer couplings will enable the modulation of the exchange anisotropy, critical temperatures (TN), and critical magnetic fields (Bc). In addition, the single-ion anisotropy in these systems will be manipulated by modifying the spin quantum number. The materials discovery effort will be complemented by extensive characterization and theoretical work. Magnetic-field and/or pressure-induced quantum criticality may lead to unusual phases, such that abrupt changes in behavior can occur due to instabilities in the magnetic system which ultimately drive phase transitions. Undergraduate student involvement in every facet of the project will stimulate their growth and enthusiasm as young scientists, as well as provide them with the necessary background to begin graduate work in the future or to go on to careers in the physical sciences. This research project receives support from the Division of Materials Research and the Chemistry Division.

Project Report

Contributions within Discipline: The overarching goal of our program was to understand the interplay between structure and magnetism in complex materials. This NSF funded program advanced work on metal-organic compounds where the magnetic energy scales were small enough to allow systematic tuning by pressure, chemical modification, and/or high magnetic fields. Concomitantly, our efforts were interdisciplinary in nature and relied on extensive synthetic and characterization strategies to reveal crystal structures and magnetic behavior. Aside from the use of organic building blocks such as pyrazine (pyz) and related molecules in our work, we also incorporated very strong, yet flexible hydrogen bond components of the O-H···F and F···H···F type. This led to spatial exchange anisotropy owing to the presence of different magnetic pathways. For instance, in the [M(HF2)(pyz)2]X (M = Ni, Co, Cu; X = BF4, PF6, SbF6) family of coordination polymers, we found that the magnetic interaction along Cu-FHF-Cu was weak (or possibly negligible) whereas Cu-pyz-Cu was quite strong. The opposite was true for Ni and Co analogs where we observed Ni-FHF-Ni and Co-FHF-Co interactions to be about 10 times stronger than along Ni-pyz-Ni and Co-pyz-Co. The differences in magnetic structure stemmed from orbital occupations wherein the Cu ion has one less magnetic electron than Ni and two less than Co. Goodenough-Kanamori-Anderson rules, which were developed for metal-oxide systems, still apply to our compounds despite the more complex molecular orbitals that facilitate the magnetic couplings between metal ions. Nearly two-fold increases in magnetic ordering temperatures were discovered in the Ni and Co systems as compared to Cu. Importantly, our materials provided important counterparts to systems with much higher energy scales (such as cuprates and iron pnictides) and as such, we were able to manipulate field/temperature phase diagrams. We continue to carefully evaluate the data obtained through this project in order to establish the commonality between our molecule-based systems and cuprates and iron-pnictides. Contributions to Other Disciplines: Our program has natural ties to the materials design community, solid state chemistry and physics, and to theorists interested in functional materials. Furthermore, we expect our findings to broadly impact the general understanding of magnetic order in the undoped cuprate oxides and iron pnictides, as well as materials under extreme conditions. Examples included the preparation of new functional materials, the understanding of magnetic processes and how they are coupled with other degrees of freedom, fundamental aspects of physical inorganic chemistry and new synthetic methodologies. Contributions to Human Resource Development: This NSF funded program significantly contributed to the diversity of our research team. Over the 3-year span of this project, EWU personnel that were directly involved included four male and nine female undergraduate research assistants (most of whom went on to graduate or other advanced degree granting institutions). Seven of the thirteen students are currently enrolled in PhD programs at Texas A & M University (chemistry), University of California-Irvine (chemistry), University of Alaska-Fairbanks (physics), University of Washington (chemistry), and the University of Utah (chemistry). Two other students, one male and one female, are currently enrolled in pharmacy school at Washington State University. During the fall of 2013, one student began her undergraduate career at Embry-Riddle Aeronautical University in Arizona. Contributions to Resources for Research and Education: Eastern Washington University is a predominantly undergraduate teaching institution and as such, little research infrastructural resources were available. With supporting funds from this NSF award, an inert-atmosphere glovebox and solvent purification system were purchased which greatly expanded our synthetic capabilities and tools available to our group and others working in the Department. Moreover, this gave undergraduates additional laboratory experience in handling air- and/or moisture-sensitive chemical compounds. The many opportunities borne by NSF’s support enhanced our students’ level of preparedness for graduate school and/or other professional programs. Several students presented posters at the EWU research symposium held every May. One student presented a poster at the International School and Symposium on Multifunctional Molecule-Based Materials held in France. Three different students accompanied the PI to the NHMFL-Los Alamos to participate in high magnetic field experiments on samples synthesized by undergraduate students at EWU. It should be mentioned that students and postdocs working with collaborators also benefitted from involvement on this project as it provided the needed materials for them to study as part of their doctoral and postdoctoral work.

Agency
National Science Foundation (NSF)
Institute
Division of Materials Research (DMR)
Type
Standard Grant (Standard)
Application #
1005825
Program Officer
Guebre X. Tessema
Project Start
Project End
Budget Start
2010-09-01
Budget End
2013-10-31
Support Year
Fiscal Year
2010
Total Cost
$265,000
Indirect Cost
Name
Eastern Washington University
Department
Type
DUNS #
City
Cheney
State
WA
Country
United States
Zip Code
99004