The optical functions of AlN thin films deposited on the quartz substrates by the reactive radio frequency magnetron sputtering, such as refractive index, extinction coefficient, optical band gap, and film thickness were determined from the transmittance and reflectance spectra in the range of 190-820 nm. For these analyses, an inverse synthesis method was established after literature survey. The results were doublechecked with a modified envelope method, and compared with those of previous reports. Spectroscopic ellipsometry analyses were performed to confirm the accuracy of the methods. Refractive indices of AlN films in this study were in the range of 1.95-2.05 at 633 nm and 2.26-2.38 at 250 nm, depending on the preparation conditions. The extinction coefficients were small (Ͻ5ϫ10 Ϫ4 ) and nearly constant at low energy region ͑Ͻ2 eV͒, but exhibited various dispersion features at 2.2-3.5 eV, indicating different amount and kinds of defects of AlN films. The absorption coefficient at near-band-gap energy exhibited a strong thickness dependence, resulting in various optical band-gap energies ranging 5.34-5.71 eV.

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As part of our effort to evaluate substituted barium ferrites for particulate magnetic recording,1 we have obtained room-temperature Mössbauer spectra for BaFe12−2xCoxTixO19 (CoTi), with x=0, 0.15, 0.30, 0.45, 0.60, 0.75, 0.80, 0.85, and 0.90. With increasing x, resolution steadily worsens as the 12-K lines broaden and change shape, but monotonic trends are evident for all spectral features, suggesting a gradual change in site occupation and local atomic environment. Following our earlier work on the well-resolved CoMo spectra (up to x=2.0),2 we have successfully fit a five-site Lorentzian model for x<−0.45, however with the 12-K peak width varying independently of the other sites. A three-site model fits the main features of all spectra with a nearly linear decrease with x of hyperfine field (ionic moment) of ∼13%, 11%, and 9%, respectively, for the 4fvi, 4fiv, and 12-K sites, while the 12-K spectral area and hence site occupation increases; this is in contrast to CoMo, where the fields are independent of x and the 12-K area decreases with x. The correct fitting model is of course more complex than either of these, but is greatly clarified by the use of magnetically oriented absorbers with the gamma rays passing parallel to the magnetization direction. This procedure removes lines 2 and 5 from the sextet components and allows the full shape of 12-K lines 1 and 6 to be observed. We will discuss the results obtained in this way and relate them to trends in the bulk magnetic properties of CoTi-substituted barium ferrite.