Precipitation of magnetite from yttrium iron silicate glass

摘要

Oxide glasses containing a large amount of rare earth elements show the Faraday effect [1-3], which is applicable to an optical isolator. However, these oxide glasses are paramagnetic at room tem-perature, and possess very low paramagnetic Curie temperatures [4,5], so that high external magnetic field must be applied to attain high magnetization and large Faraday rotation angle in these materials. In general, the random arrangement of magnetic moments in oxide glasses leads to a substantial descent of magnetic transition temperature [6]. In some cases, the correlation among magnetic mo-ments does not extend to the long range, but is restricted within magnetic clusters of finite size, and the frustration of magnetic moments occurs in the boundary region among clusters [7-12]. Such a magnetic structure makes the ferro- or ferrimagnetic order unstable. Therefore, ferro- and ferrimagnet-ism with high Curie temperatures hardly take place in oxide glasses. Nonetheless, glass is an attractive material because of ease of forming any shapes such as fibres and thin films. One way to produce high magnetization in oxide glass is to introduce huge magnetic moments such as magnetization vectors of ferro- or ferrimagnetic microcrystals. The incorpora-tion of magneto-optical microcrystals into glass is also useful for the construction of waveguides equipped with isolators. Magneto-optical properties of magnetic fine particles such as Ni, Co and Cd1_v.MnvTe incorporated into several matrices were reported recently [13-16]. Magnetite, Fe3O4, is one of the compounds which show large magneto-optical effects. The Verdet constant of Fe3O4 thin film was reported to be 2.2 rad A"1 for light with a wavelength of 632.8 nm [17]. Studies on the crystall-ization of Fe3O4 from sodium silicate [18] and calcium silicate [19] glasses have been carried out. Nonetheless, it is useful to examine other glass systems containing Fe3O4 particles from the view-point of preparation of new magneto-optical mater-ials. In the present investigation, an attempt was made to prepare yttrium silicate glass containing Fe3O4 particles by heat-treating yttrium iron silicate glass. The magnetic properties of the resultant materials are reported.