DIRECT MEASUREMENT OF SUPERPARAMAGNETIC FLUCTUATIONS IN MONODOMAIN FEPARTICLES

Neutron spin-echo spectroscopy was used to resolve for the first time the slow relaxation component associated with the fluctuations of the whole spin particle in monodomain Fe particles in an alumina matrix. T hese fluctuations are progressively freezing with decreasing temperatu re. A distribution of relaxation times was observed most likely due to a finite particle size distribution. As a result, one will have to me asure at significantly longer Fourier times in order to quantify the f reezing behaviour. (C) 1998 Elsevier Science B.V. All rights reserved.