This project combines experiment and theory towards the designed preparation and subsequent characterization and thorough understanding of new intermetallic ferromagnets and antiferromagnets. It is based on collaboration between Iowa State University and RWTH Aachen in Germany. The primary concept involves using a complex 4d metal-boride framework with magnetic 3d elements, e.g., Cr, Mn, Fe, Co and Ni, inserted in voids to create magnetic structures with potentially low-dimensional character. The metal-boride framework provides a structurally strong and electronically robust network for insertion of magnetic metals into channels. Furthermore, the metal-boride structure is intrinsically metallic, which provides a mechanism for magnetic exchange between adjacent magnetic metal atoms via the spins on the conduction electrons. Specifically, these materials are studied by X-ray and neutron diffraction as well as magnetization experiments to determine atomic and magnetic structures. Theoretical determination of the electronic structures on various models of these structures provides feedback toward further synthetic efforts of atomic substitutions to create new compounds with targeted magnetic behavior. At present, chemists and materials scientists have no general, yet simple, rules for targeting and tailoring ferromagnetic, intermetallics compounds, i.e., metallic compounds with permanent magnetic behaviour. This effort allows chemists to study an evolution of magnetic behaviour within a single structural family to identify trends in magnetic behavior as various chemical and physical parameters change in systematic ways.
A project such as this, that combines experiment and theory for condensed matter systems, provides students a truly interdisciplinary problem - these students learn how different scientific subjects and models impact other scientific areas. The student participants in this project in Aachen, Germany and Ames, Iowa have opportunities for exchange, and they learn both experimental and theoretical components of research in solid-state chemistry. Furthermore, through this systematic study of a structural family, a set of rules will be generated for targeting metallic, permanent magnets, which have numerous technological applications. The real challenge will be to identify the temperature range where such targeted materials will show permanent magnetic behavior. In summary, this effort represents a strong, synergistic coupling of experiment and theory that targets new magnetic materials, and may lead to new materials with unusual bulk magnetic properties due to the potential one-dimensional character of the magnetic exchange.
The study of magnetism is useful for energy-related technology. Magnetic effects in materials originate from the electrons that are also involved in chemical bonding. In some materials, these electrons also contribute to electrical conduction - these electrons are called "itinerant" and the resulting magnetic effects are called "itinerant magnetism". This project (DMR-0806507) is a collaboration with a group in Aachen, Germany to examine complicated but robust chemical structures that contain magnetically active metals like chromium, manganese, iron, cobalt, and nickel in fragments that resemble wires, ladders, and scaffolds. The research entailed materials preparation, using high temperature and air-sensitive techniques, structural characterization by x-ray diffraction, magnetization studies, and analysis of their electronic structure using first-principles theory. During this project, several new compounds were discovered. These new compounds allowed systematic variation in chemical composition so that magnetic behavior could be correlated with chemical content. Development of a theoretical model that could explain the changes in magnetism with chemical composition demonstrated how magnetism is tied to chemical bonding in metal-rich compounds. Another theoretical outcome is an ability to predict the occurrence of ferromagnetism, which is spontaneous bulk magnetization, by using analysis of the electronic structure. This work is currently being extended to explore other transition metals and other structural fragments of magnetically active metals to establish firm relationships among chemistry, structure, and magnetic behavior. Our hope is establish certain chemical guidelines that will help tailor new magnets with desired properties. One major factor that still requires development is an ability to predict the temperature range over which spontaneous magnetization (ferromagnetism) exists. As a project supported by the Materials World Network program, one graduate student from my group at Iowa State University and one student from the Technical University in Aachen, Germany exchanged seats over 3-4 weeks to visit the each other's institutions. These student experiences included conducting research in the other collaborating group, giving a public presentation to the departments during their respective visits, and learning about the academic cultures in each country. Also, their ability to visit each others groups enhanced the collaboration and furthered scientific advancement on the project. The ISU student completed his doctoral studies and is now pursuing a post-doctoral appointment in advanced materials research with a goal toward entering academia.
