Takehito Nakano

Optical studies of nanoscale materials incorporated in the space of zeolite crystals

Abstract Optical spectroscopy is used for the characterization of the quantum electronic state of nanoscale materials incorporated in zeolite crystals. Alkali metal clusters generated in zeolite exhibit interesting phenomena in optical properties as well as magnetic ones. Potassium clusters incorporated in zeolite LTA have shown ferromagnetism at low temperatures. The origin of the ferromagnetism was explained by the itinerant electron model. The infrared spectrum and magnetization curves, however, suggest that the itinerant electron model is not applicable to the ferromagnetism. Magnetic properties are interpreted based on the model of ferrimagnetism. Polarized micro-optical spectroscopy suggests the possibility of the one-dimensional array of potassium clusters in zeolite MOR single crystal

Loading density dependence of ferromagnetic properties in potassium clusters arrayed in a simple cubic structure in zeolite LTA

Magnetic properties are investigated for potassium clusters arrayed in zeolite LTA. The potassium loading density per cluster, n, is changed up to 7.2 per cluster. The n-dependence of the Curie constant and the magnetization are measured in detail. Possible origins of ferromagnetic properties are discussed. ( 2000 Elsevier Science B.V. All rights reserved.

Ferromagnetic properties of rubidium clusters in zeolite LTA

Abstract Magnetic and optical properties of Rb clusters in aluminosilicate zeolite LTA are investigated in detail. These clusters are stabilized in supercages arrayed in a simple cubic structure. The average number of s-electrons confined in each cluster, n , is changed up to the nearly saturated value ∼4.6. At n >2, the absolute value of the negative Weiss temperature increases with increasing n . In saturated samples at n ∼4.6, ferromagnetic properties are observed below the asymptotic Curie temperature 3xa0K, but the fraction of the spontaneous magnetization is found to be very small and incomplete. Magnetic properties are different from those of K clusters in LTA, and discussed in relation to residual K cations.

Optical and ESR Studies of Na Clusters in Zeolite FAU

Abstract Na clusters are generated in zeolite FAU with Si-to-Al ratios of 2.8 (Y-type) and 1.25 (X-type). When the density of adsorbed Na atoms increases, the ESR spectrum with hyper-fine structures becomes narrow into a single line. In the IR absorption spectrum, no Drude-like absorption is observed at any adsorption densities of Na atoms. The ESR narrowing is explained by the mean field theory of the exchange narrowing given by Anderson and Weiss, by using the experimentally observed antiferromagnetic exchange coupling energy between magnetic moments of clusters.

Magnetic and optical properties of K and Na clusters arrayed in a diamond structure in zeolite FAU

K and Na clusters are generated in zeolite FAU with an Si-to-Al ratio of 1.25. We measured magnetic susceptibility, electron}spin resonance spectrum and the optical one. Observed magnetic properties are discussed from the viewpoint of the correlated electrons and/or the narrow energy band with a properly localized nature of clusters, together with a nite disorder e!ect. ( 2000 Elsevier Science B.V. All rights reserved.

Magnetic Properties Near the Ferromagnetic-Nonferromagnetic Phase Boundary in Potassium Clusters Incorporated into Zeolite LTA

Abstract Magnetic and optical properties are investigated for K clusters incorporated into zeolite LTA at loading densities of K atoms, n, between 1.0 and 3.2 per cluster. No magnetic ordering is observed at n < 2. The spontaneous magnetization due to ferromagnetism is observed suddenly at n > 2. It is confirmed that the 1p-like quantum electronic state of K cluster plays an essential role in the ferromagnetic phase.