THEORY OF NANOMAGNETS

Research Foundation Of The City University Of New York (Lehman), Bronx NY

Investigators

Abstract

TECHNICAL SUMMARY: This award supports theoretical research and education on quantum dynamics of many spins interacting with phonons and concentrates primarily on applications to molecular nanomagnets. New directions under investigation include theories of magnetic avalanches, rotation-induced magnetism, and the occurrence of long-range spin-spin correlations due to spin-phonon coupling. The improved theory for magnetic avalanches is motivated by the need for understanding the phenomenon of magnetic deflagration observed in crystals of molecular magnets. Mechanisms initiating ignition and subsequent propagation of the magnetic flame are investigated. In addition an alternative theoretical model, based upon a propagating Landau-Zener wave, using analytical and numerical methods is being compared to this theory. The possibility that magnetic detonation is driven by non-linear dynamics of spins coupled with lattice deformations is being investigated. In addition, a theoretical method that addresses the possibility of observing the quantum Barnett effect in magnetic nanoparticles is being developed. This theory considers the coupled dynamics of a magnetic moment of a free particle with the mechanical rotations. The Interaction of spins with high-frequency large-amplitude sound waves will be investigated with an emphasis on dynamical spin-rotation coupling. This research addresses the possible direct observation of spin-rotation coupling in crystals of molecular magnets. Collective behavior due to an ensemble of weakly coupled spins interacting with phonons is a being studied to determine the role that coherent phonons play in providing long-range correlations between the spins. This study connects with the phonon bottleneck, non-radiative spin-phonon states, and coherent amplification of spin phonon relaxation will be studied in application to molecular magnets. The dependence of the spin-lattice relaxation on the size of the magnet will be investigated. Graduate and undergraduate students, as well as high school students will be actively involved in this research. This project involves international collaborations. NON TECHNICAL SUMMARY This award supports theoretical research and education aimed at a fudamental understanding of magnetism on the nanoscale and the discovery of new phenomena involving nanomagnets. In addition to improving fundamental scientific understanding of the breakdown of classical physics as materials approach the nanoscale size regime, molecular magnetic materials and other nanoscale magnetic particles are expected to positively impact a broad range of technologies. Examples include magnetic resonance imaging technologies, magnetic recording and more novel information technologies such as spintronics, which seeks to exploit the magnetic properties of electrons as well as their charge in new devices and quantum computing. The performance and operating environment of these nanoscale particles is strongly influenced by the way the magnetic particles interact with neighboring particles as the macroscopic material stretches, bends and distorts. Theories to account for these interactions are being developed in parallel with the discovery of potentially useful effects that arise because of these interactions. Possible future technological advances based on these effects include an acoustic analog of the laser, beam rotation induced magnetic effects at the nanoscale and a feature known as magnetic deflagration. Magnetic deflagration is the magnetism analog of the ignition and subsequent spread of flames. However in molecular-magnetic materials the process is reversible which provides the potential for expanding our understanding of combustion in a novel way. Graduate and undergraduate students, as well as high school students will be actively involved in this research. This project involves international collaborations.