Studies of Mesoscopic Spin Systems: Magnetic Molecules and Formalism

Northwestern University, Evanston IL

Investigators

Abstract

This award supports theoretical research and education in the study of magnetic macroscopic quantum phenomena and large magnetic molecules. The PI will investigate: (a) the magnetic properties of solids containing large magnetic molecules, (b) the semiclassical formalism for spin, and (c) unresolved physical issues in magnetic macroscopic quantum phenomena. The observations of hysteresis loop steps in the compounds commonly abbreviated Mn 12 and Fe 8 and oscillatory tunnel splittings in Fe 8, have opened new areas for the study of spin dynamics with novel interplays of quantal and classical behavior. The PI will study these single molecule magnets, especially the way in which they interact with their solid state environment. As an example, the PI will study how the sound propagation in these materials is affected by the magnetization dynamics, as a way of probing the latter. These studies are expected to elucidate magnetic hysteresis at the molecular level and to lead to ways of manipulating the dynamics of such systems. The formalism of the semiclassical limit for spin will be studied with a view to remedying gaps in present understanding. The physical origin of a rich and unexpected structure of degeneracies that has been discovered in models for Fe 8 and rotating nuclei will be sought. These degeneracies suggest an as yet undiscovered 'higher symmetry.' The PI will also exploit connections between molecular magnets and macroscopic quantum phenomena in magnets to examine outstanding questions that may impact future attempts to look for magnetic macroscopic quantum phenomena. This research also provides an environment for training of doctoral students at the frontiers of theoretical condensed matter physics. %%% This award supports theoretical research and education in the study of magnetic macroscopic quantum phenomena and large magnetic molecules. The work focuses on large molecules that have a large spin associated with them. The spin is large enough that it can be considered to be macroscopic, but at the same time small enough to exhibit various quantum mechanical phenomena, such as quantum mechanical tunneling of the spin orientation. Two examples of families of these large molecules are Mn12 and Fe8, in a standard shorthand notation. The PI will investigate: (a) the magnetic properties of solids containing large magnetic molecules, (b) the semiclassical formalism for spin, and (c) unresolved physical issues in magnetic macroscopic quantum phenomena. This work contributes to the intellectual foundation of quantum mechanical and magnetic phenomena in real materials and may contribute to future information and communication technologies. This research also provides an environment for training of doctoral students at the frontiers of theoretical condensed matter physics. ***