Magnetic properties of Hagi ware

抄録

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, Fe₂O₃. The magnetic moment of the Daido clay (which only contains a small amount of the Fe₂O₃ γ-phase) attains a maximum at a firing temperature of approximately 600°C, where a minor amount of the poorly crystallized Fe₂O₃ temporarily changes to the ferromagnetic γ-phase. Furthermore, the magnetic moment of the Mishima clay (which contains a large amount of the Fe₂O₃ γ-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 γ-phase and a major α-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 γ-phase of Fe₂O₃ to the α-phase of Fe₂O₃. This transformation is considered to contribute to the change from soft magnetism to hard magnetism of Hagi ware.