Ferromagnetism and paramagnetism in potassium clusters incorporated in zeolite LTA

Magnetic and optical properties are investigated for potassium clusters incorporated 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 negative Weiss temperature -35 EC is seen at 3.5 atoms per cluster, and gradually approaches the Curie law as the loading density increases up to 7.2 atoms per cluster. The Curie temperature, similar to 8 K at 3.5 atoms per cluster, approaches 0 K at 7.2 atoms per cluster. These results suggest that the antiferromagnetic coupling between localized magnetic moments of K clusters decreases with increasing K-loading density, and almost disappears at the K-loading density of 7.2 atoms per cluster. The insulator-like absorption tail is observed in the infrared region at any loading density, indicating that K clusters in LTA are in the Mott insulator phase. The average magnetic moment estimated from the saturation magnetization remarkably increases 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 estimated from the Curie constant is similar to 1.6 mu(B) per cluster, and almost independent of the loading density. The explanation of these magnetic properties by the model of ferrimagnetism proposed in a previous paper proves difficult.