Reflectivity spectra of all rare-earth hexaboride RB6 I', R =La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Y) single crystals have been measured systematically in the energy region from 1 meV to 40 eV at 300 K in order to investigate the electronic state and the contribution of the 4f electron to the band structure. The analysis of the optical conductivity and the loss-function spectra, which were derived from the Kramers-Kronig transformation of the reflectivity spectra, allowed us to make clear the origin of the peak structure in the spectrum due to the various interband transitions. The origins of the main peaks in the spectrum were assigned to the interband transitions from the bonding to the antibonding bands of the boron Zs and 2p states and to the rare-earth 5d state. The intra-atomic transition from the 4f and the Sp to the Sd(tzs ) states in the rare-earth ion was also observed.

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Hagi ware originally consists of a mixture of two raw materials: Daido clay and Mishima clay. During its firing process, we observed a change in the magnetic properties of the iron oxide, Fe 2 O 3 . The magnetic moment of the Daido clay (which only contains a small amount of the Fe 2 O 3 £-phase) attains a maximum at a firing temperature of approximately 600°C, where a minor amount of the poorly crystallized Fe 2 O 3 temporarily changes to the ferromagnetic £-phase. Furthermore, the magnetic moment of the Mishima clay (which contains a large amount of the Fe 2 O 3 £-phase) decreases as the firing temperature increases, whereas the coercive field rapidly increases at firing temperatures above 1000°C. The magnetization curve of the Mishima clay that was fired at temperatures above 1200°C is characteristic of a two-component system consisting of a minor £-phase and a major ¡-phase. The above-mentioned phenomena were also confirmed by XRD analyses. A series of experiments indicated that the firing of Hagi ware can be characterized as a transformation from the £-phase of Fe 2 O 3 to the ¡-phase of Fe 2 O 3 . This transformation is considered to contribute to the change from soft magnetism to hard magnetism of Hagi ware.