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Magnetic and optical properties of silica-gel glass containing iron oxide fine particles

Glassy composite materials containing oriented magnetic fine particles are expected to have large residual magnetization and coercive force because of their fine magnetic domain structure, and also to show magnetic and optical anisotropy which result from their oriented dispersive condition. The silica (SiO2) gels and glassy materials containing oriented magnetite (Fe3O4) fine particles were prepared by sol-gel method. The magnetic anisotropy of the samples were investigated by ferromagnetic resonance (FMR) spectra. The samples had uniaxial magnetic anisotropy that was evaluated from the angle dependence of FMR spectra. The coercive force of the glassy material was much larger than that of the gel because of the stress induced by the densification of the gel. Magneto-optical property of the samples was evaluated by the measurement of Faraday rotation angle in visible light region under no external magnetic field. The gel showed positive Faraday rotation with maximum at around 470 nm, however, the wavelength of maximum shifted to 700 - 800 nm in glassy sample. The Faraday rotation of both gels and glassy materials with no magnetic field was induced by the residual magnetization of the magnetite fine particles, and the change of magneto-optical spectra after densification also suggests the magnetite fine particles were subjected to the stress in the glassy materials.