Effect of partial site occupation on the magnetic properties of Nd2Fe17-xSix by supercell calculation

The magnetic properties of the Nd2Fe17-xSix intermetallic compounds are studied by means of spin-polarized supercell calculations in which the selected sites of substitution are close to the situations in real samples. It is shown that the average Fe moment increases with x and saturates near x = 3. This correlates quite well with the experimental dependence of Te on x. The difference between supercell and unit cell calculations are pointed out and the influence of Si atoms on the density of states of the nearby Fe atoms is emphasized. (C) 1997 American Institute of Physics.

Preparation and characterization of erbium doped sol-gel silica glasses

Erbium-doped silica glasses were made by sol-gel process. Intensive photoluminescence (PL) spectra from the Er-doped silica glasses at room temperature were measured. A broadband peak at 1535 ma, corresponding to the I-4(13/2)-I-4(15/2) transition, its full width at half-maximum (FWHM) of 10 nm, and a shoulder at 1546 nm in the PL spectra were observed. At lower temperatures, main line of 1535 nm and another line of 1552 Mn instead of 1546 nm appear. So two types of luminescence centers must exist in the samples at different temperature. The intensity of main line does not decrease obviously with increasing temperature. By varying the Er ion concentration in the range of 0.2 wt% - 5wt%, the highest photoluminescence intensity was obtained at 0.2wt% erbium doped concentration. Luminescence intensity decreases with increasing erbium concentration. Cooperative upconversion was used to explain the concentration quenching of luminescence from silica glass with high erbium concentration. Extended X-ray absorption fine structure measurements were carried out. It was found that the majority of the erbium impurities in the glasses have a local structure of eight first neighbor oxygen atoms at a mean distance of 0.255 nm, which is consistent with the typical coordination structure of rare earth ion.