Preparation and Characterization of Transparent Magnetic Oxide Meterials

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Transparent magnetic oxide materials are useful as magnetooptical devices and windows for shielding of magnetic fields. The aim of the present research is to prepare new transparent magnetic oxide materials and to characterize the magnetic, optical, and magnetooptical properties of the resultant materials. The main results of the research can be summarized as follows :(1) Faraday effect measurements have been carried out at room temperature for some sodium borate glasses containing Eu^<2+> ions prepared under a reducing atmosphere. The wavelength dependence of the Verdet constant is analyzed in terms of a theory derived by Van Vleck and Hebb to obtain effective transition wavelength of the 4f^7*4f^6 5d transition which canuses the Faraday effect of Eu^<2+> in the visible range. The effective transition wavelength increases with an increase in the optical basicity of glass. This phenomenon is explained in terms of the crystal field theory ; because the splitting of 5d levels is larger i … More n the glass with larger optical basicity, the energy required for the 4f^7*4f^6 5d transition decreases as the optical basicity of glass increases. The magnitude of Verdet constant increases with an increase in the effective transition wavelength when the concentration of EuO remains constant.(2) We have examined the effect of heat treatment temperature and time on the magnetic properties of rapidly quenched oxides with compositions close to ZnFe_2O_4, which show high magnetization even at room temperature as we found. In particular, an attention is focused on the oxide with nominal composition of 60ZnO・40Fe_2O_3. X-ray diffraction, Zn K-edge extended X-ray absorption fine structure (EXAFS), Mossbauer spectroscopy, and magnetization measurements are carried out to clarify the variation of crystal structure and magnetic properties with heat treatment. The rapidly quenched specimen contains zinc ferrite with lattice parameter 0.05% smaller than that of ZnFe_2O_4 as the main phase, and exhibits the magnetization of 23.8 emu/g at room temperature. The X-ray diffraction, EXAFS and Mossbauer measurements suggest that the high magnetization is brought about by the Fe^<3+> ion clusters with the Zn^<2+> ions occupying octahedral sites as well as the solid solution of Fe_3O_4 in the ZnFe_2O_4. As the heat treatment temperature increases, the room temperature magnetization decreases sluggishly below 500ﾟC and decreases sharply above 600ﾟC when the heat treatment time is 2h. The variation of EXAFS and Mossbauer spectra with heat treatment temperature suggests that the decrease of magnetization below 500ﾟC corresponds to the transfer of Zn^<2+> ions from octahedral to tetrahedral sites while the rapid decrease of magnetization above 600ﾟC is caused by the oxidation of Fe^<2+> to form ZnFe_2O_4 with normal spinel structure. A complicated behavior is observed at around 550ﾟC ; the magnetization once increases at 550-600ﾟC and then decreases rapidly as the heat treatment temperature increases. We speculate that at the initial stage of the oxidation of Fe^<2+>, vacancies of Fe^<3+> ions at the octahedral sites are created, leading to the increase of magnetization. Less