IRON CLUSTERS SUPPORTED IN A ZEOLITE MATRIX - COMPARISON OF DIFFERENTMAGNETIC CHARACTERIZATIONS

Metallic iron clusters dilutely supported in zeolite NaX have been stu died by magnetization, ac susceptibility, and transmission electron mi croscopy. Their behavior is superparamagnetic at high temperatures wit h negligible intercluster interactions and the cluster magnetic moment s become blocked at low temperatures. From the ac susceptibility data, at frequencies between 1 HZ and 1 kHz in the temperature range 1.8-30 0 K, the distribution of activation energies has been determined. The results have been used to check a previously proposed scaling of the a c susceptibility and justify the use of the Arrhenius law for these sy stems. Although the obtained information is limited by the temperature and frequency window of the experiment, the quantitative analysis of the ac susceptibility provides, with respect to the magnetization data , additional information about the actual distribution of cluster size s and it is a valuable tool to avoid misinterpretations about the inte raction effects.