Magnetic Nanoparticles: The Simulation of Thermodynamic Properties

Magnetic materials are now controllable down to a nanometer length scale and, hence, there is a broad interest in the understanding of magnetic phenomena in nanostructured systems. With decreasing size thermal activation becomes more and more relevant and the understanding of the role of temperature for the dynamic behavior and for the magnetic stability of ferromagnetic nanostructures is an important subject in micromagnetism. It is interesting from a fundamental point of view as well as for applications in magnetic devices. In this article, an overview is given on numerical approaches for the investigation of thermodynamic properties of magnetic systems, described by classical spin systems. As an example, magnetization reversal in nanostructures is simulated over a wide range of time-scales, from fast switching processes on a picosecond time-scale to thermally activated reversal on a microsecond time-scale. Langevin dynamics is used as well as a time quantified Monte Carlo method for the simulation of elongated Co nanoparticles. We study the behavior of the magnetization during the reversal, the energy barriers which are relevant for the thermally activated longtime behavior and the corresponding characteristic times.