Duong Thi Hanh

Ferromagnetism of Na-K Alloy Clusters Incorporated in Zeolite Low-Silica X

In a porous crystal of zeolite low-silica X (LSX), β-cages and supercages (cavities) are arrayed in a diamond structure, respectively. We loaded potassium metal into zeolite LSX which has a chemical formula of Na7.3K4.7Al12Si12O48 per β-cage (or supercage), and generated Na–K alloy clusters in β-cages and/or supercages. We have investigated the magnetic properties, the optical ones and the electrical resistivity at various values of K-loading density n per β-cage (or supercage) up to n = 9.7. Localized magnetic moments are observed at 8.2 < n < 9.7. Almost simultaneously, nearly pure ferromagnetism is observed at 8.4 < n < 9.7. The highest Curie temperature is ≈12 K at n ≈ 9. Optical reflection spectra for 8 < n have a new band at 2.8 eV which is assigned to the optical excitation of s-electrons of clusters generated at β-cages. The origin of the magnetic moments is assigned to these β-cage clusters because of the coincidence between the growths of the 2.8 eV band and localized magnetic moments. The origi...