NSF-Europe: Collaborative Study of Geometrically Frustrated Magnetic Material: New Materials and New Physics

Pennsylvania State Univ University Park, University Park PA

Investigators

Abstract

This is an international collaborative research project that was submitted in response to NSF Solicitation NSF 02-135. The project will investigate the unusual properties of geometrically frustrated magnets, materials in which the interactions between atomic spins compete with each other due to the triangular geometry of the magnetic sublattice. This leads to highly degenerate ground states where the interaction energies cannot all be simultaneously minimized. This in turn prevents ordinary magnetic ordering down to temperatures well below the energy scale of the spin-spin interaction. The low temperature magnetic properties will be investigated via a collaborative approach involving two U.S. investigators, who specialize in materials chemistry and magnetothermodynamic measurements, and two European groups: One in the areas of nuclear magnetic resonance (NMR) and other measurements at Laboratoire de Physique des Solides, Universite Paris-Sud, the other in the areas of neutron diffraction and theory at University College London. One research theme is the chemical synthysis of new geometrically frustrated magnets with the specific goals of investigating new frustrating lattice types and of finding materials that are both highly frustrated and that can be grown as high-quality single crystal samples. The second theme is the study of effects of chemical substitution on geometrically frustrated systems. Students involved in the research will participate in international research activities, together with traditional and cutting edge training that will prepare them for careers in academe, industry or government. %%% This is an international collaborative research project that was submitted in response to NSF Solicitation NSF 02-135. The project will investigate the unusual properties of a class of materials known as geometrically frustrated magnets. In contrast to ordinary magnets, and due to the geometrical arrangement of magnetic atoms in the lattice, these materials cannot attain a unique, low temperature, lowest-energy arrangement for their magnetic moments. The key geometry leading to the effect has magnetic atoms placed at the vertices of triangles. These systems are fundamentally different from other magnetic materials in that their properties at low temperatures cannot be understood within current theoretical models. Understanding geometrical frustration in magnets has implications for complex systems as diverse as superconducting junction arrays or neural networks, and may also provide insight into computational algorithms. The research is a collaboration between four groups, two in the U. S., one in the United Kingdom and one in France. The two U.S. investigators have a long record of working with a diverse group of students and involving graduate students and undergraduates in every stage of the research process. Students involved in the research will participate in international research activities, together with traditional and cutting edge training that will prepare them for careers in academe, industry or government.