Ferromagnetism and paramagnetism in potassium clusters incorporated in zeolite LTA

Magnetic and optical properties are investigated for potassium clusters inc orporated in zeolite LTA at loading densities of K atoms between 3.5 and 7. 2 per cluster, the latter of which is saturated. The Curie-Weiss law with n egative Weiss temperature -35 EC is seen at 3.5 atoms per cluster, and grad ually approaches the Curie law as the loading density increases up to 7.2 a toms per cluster. The Curie temperature, similar to 8 K at 3.5 atoms per cl uster, approaches 0 K at 7.2 atoms per cluster. These results suggest that the antiferromagnetic coupling between localized magnetic moments of K clus ters decreases with increasing K-loading density, and almost disappears at the K-loading density of 7.2 atoms per cluster. The insulator-like absorpti on tail is observed in the infrared region at any loading density, indicati ng that K clusters in LTA are in the Mott insulator phase. The average magn etic moment estimated from the saturation magnetization remarkably increase s from 0.25 to 0.15 mu g per cluster as loading density increases from 3.5 to 7.2 atoms per cluster. On the contrary, the average magnetic moment esti mated from the Curie constant is similar to 1.6 mu(B) per cluster, and almo st independent of the loading density. The explanation of these magnetic pr operties by the model of ferrimagnetism proposed in a previous paper proves difficult.