Influence of particle size distribution on the initial susceptibility of magnetic fluids in the Brown relaxation range

We present experimental results on magnetic liquids characterised by a size distribution of particles. The initial complex susceptibility has been studied in the Brown relaxation range using a polarimetric method. The position and the shape of the relaxation peak allow to determine apparent values of hydrodynamic mean diameter and its standard deviation. Theoretical calculations were made from the Debye model including the size distribution of particles and the experimental study shows its influence and the necessity to take it into account for a better results exploitation. In these conditions, the Debye model used gives excellent results in accordance with the experimental points. (C) 1998 Elsevier Science B.V. All rights reserved.