Dynamics of fine particles observed in zero-field neutron scattering

We present here a dynamical study of Fe particles (○/∼50 Å) dispersed in an alumina matrix, performed by inelastic neutron scattering, in zero applied field. The line shape of the energy spectrum, quasielastic or inelastic, allows us to define three temperature ranges, attributed to three distinct regimes for the transverse fluctuations. At high temperature, the line shape is quasielastic with a nearly temperature independent energy linewidth. At intermediate temperature, one observes the expected precession mode with an inelastic line shape. At low temperature, a ‘‘reentrant’’ behavior occurs, which locates the disappearance of the precession mode, likely due to the effect of interparticle coupling.