A new magnetic material with appreciable optical transmission in the visible region at room temperature has been isolated as a gamma-Fe(2)O(3)/polymer nanocomposite. The synthesis is carried out in an ion-exchange resin at 60 degrees C. Magnetization and susceptibility data demonstrate loading-dependent saturation moments as high as 46 electromagnetic units per gram and superparamagnetism for lower loadings where particle sizes are less than 100 angstroms. Optical absorption studies show that the small-particle form of gamma-Fe(2)O(3) is considerably more transparent to visible light than the single-crystal form. The difference in absorption ranges from nearly an order of magnitude in the "red" spectral region to a factor of 3 at 5400 angstroms. The magnetization of the nanocomposite is greater by more than an order of magnitude than those of the strongest room-temperature transparent magnets, FeBO(3) and FeF(3).

Colloidal iron dispersions have been prepared by the thermolysis of Fe(CO)5 in solutions of functional polymers. The structure of the particles was very disordered at sizes ≲100 Å but changed to become single crystal with a disordered core as the size increased to 100–200 Å. Particles ≲100 Å were superparamagnetic, and particles in the 100–200-Å range had a time-dependent hysteresis. On exposure to the atmosphere an ∼30-Å-thick γ-Fe2O3 oxide film was produced on the surface of the particles. This is the ’’passive oxide film’’ detected previously by a number of techniques but never before imaged directly in situ. As water was absorbed from the atmosphere the chlorinated solvent-based dispersions reacted further to give β-FeOOH. This reaction was promoted by chloride-ion impurity. The magnetic moment decayed with oxidation roughly in proportion to the quantities of Fe, γ-Fe2O3, and β-FeOOH present. Disorder in the structure of ≲100-Å particles formed in nonchlorinated solvent-based dispersions produced an initial oxide film with magnetic characteristics distinct from those of γ-Fe2O3.

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Mossbauer and magnetization measurements have been made on a [(SiO2)45(Ca0)55]65[Fe2O3]35 glass equilibrated at 1550 °C in a variable oxygen partial pressure atmosphere. The concentration of Fe2+ cations, as determined by Mossbauer analysis, is observed to increase with lower pO2 pressures at the expense of the fraction of Fe3+ cations tetrahedrally coordinated. The Fe2+ doublet is found to display the largest isomer shift and quadrupole splitting. For the two types of ferric cations there appears to be a general tendency for the Fe3+ cations with lower coordination to have a lower isomer shift but a substantially larger quadrupole splitting. Room temperature magnetization data indicate all the samples to contain superparamagnetic particles which increase in abundance with lower pO2 pressures. The superparamagnetic behavior is attributed to the formation of ferrite precipitates which occur during quenching.

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