Seminars Archive
Relaxation of magnetization in nanomagnets
Department of Physics, Faculty of Science, University of Zagreb
Abstract
In three classes of nanomagnets: magnetic nanoparticles CuxFe3-xO4, single-molecule magnets Mn12-acetate and Mn12-formate, and magnetic clusters within amorphous alloy Hf100-xFex, we investigated slow relaxation of magnetization on the time scale of experiment. Measurements of the temperature dependence of the zero field cooled and field cooled magnetization, magnetic hysteresis loops, time dependence of magnetization and other, all point to the thermal activation of superparamagnetic moments over the potential anisotropy barriers. In Mn12-acetate the quantum tunnelling of spin of the molecule was introduced additionally, to explain the steps on hysteresis loops, resonant behaviour of the field dependence of relaxation time and anomalies in the time relaxation of magnetization. For the nanoparticles and magnetic clusters within alloy we determined from magnetic measurements the distribution of magnetic moments over anisotropy barrier heights, as well as the effective anisotropy density in nanoparticles and the size of magnetic nano-clusters in the alloy.
Nanomagnets are convenient for the investigation of classical and quantum relaxation, whose contact still has many open questions, too.
