Physical Properties of Nanometer-Scale Magnets

Abstract

Contemporary needs for increasing information storage and high density magnetic recording have stimulated new research in mesoscopic magnetism. In analogy to semiconductor physics, the process of miniaturizing magnetic materials has revealed a variety of new and unexpected classical and quantum mechanical phenomena. On a small enough length scale the interactions between individual atomic spins cause their magnetic moments to be aligned in the ordered pattern of a single domain, without the complication of domain walls separating regions of varying orientation. For particle sizes at or below that of a single domain, standard theoretical models of dynamical behavior predict simple stable magnets with controllable properties. However, recent experimental studies of micron-scale ferromagnetic particles show them to be far less stable and to switch more easily than expected from traditional classical theories of thermal activation. In even smaller systems, new theoretical predictions and experimental observations suggest that at low enough temperature, quantum mechanical tunneling may ultimately control the particle’s magnetization.