Magnetic and Optical Properties of Rb and Cs Clusters Incorporated into Zeolite A

Optical and magnetic properties are studied on Rb and Cs clusters incorporated into the cages of aluminosilicate zeolite A (structure type code LTA), where alpha and beta cages with inside diameters of similar to 1.1 and similar to 0.7 nm, respectively, are arrayed in a simple cubic structure. The average number of guest alkali atoms per alpha cage, n, was changed from dilute loading to similar to 5 and similar to 3.5 for Rb and Cs, respectively. At n > 2, the absorption coefficient at mid-infrared region increases significantly. This is assigned to a contribution of the Drude term in a metallic phase. The change from insulating phase to the metallic one is ascribed to a wider bandwidth of the 1p state of clusters compared with that of the 1s state. All samples show Curie-Weiss law with negative Weiss temperatures. In Rb clusters, both of the Curie constant and the absolute value of Weiss temperature gradually increases with increasing n at n > 2, and ferromagnetic properties are clearly found at n > 4. This n-dependence is essentially different from that in ferromagnetism in K clusters at n > 2. Cs clusters shows quite small values of Curie constant at n > 2 and also non-ferromagnetic behavior up to the maximum value of n.