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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 Na 7.3 K 4.7 Al 12 Si 12 O 48 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 origin of magnetic ordering is explained by a ferromagnetic interaction between β-cage clusters. All samples are found to be insulating from the temperature dependence of electrical resistivity. A direct magnetic interaction between β-cage clusters is not expected because of the high electronic barrier between them. A ferromagnetic superexchange coupling between β-cage clusters is newly proposed via the sp 3 -like closed-shell clusters at supercages. A thermal hysteresis is observed in the electrical resistivity at intermediate temperatures, and the origin is assigned to low-density carriers generated in the Na-K eutectic alloy structures in nanospace.

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