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 K is seen at 3.5 atoms per cluster, and gradually approaches the Curie law as the loading density increases up sto 7.2 atoms per cluster. The Curie temperature, ~ 8 K at 3.5 atoms per cluster, approaches 0 K at 7.2 atoms per cluster. These results suggest that the antiferrornagnetic 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 0.75 μ B 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 ~ 1.6 μ 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.
PACS36.40.Cg Electronic and magnetic properties of clusters 71.24.+q Electronic structure of clusters and nanoparticles 75.50.Dd Nonmetallic ferromagnetic materials
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