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991.
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Janis Kliava Irina EdelmanOxana Ivanova Ruslan IvantsovEleonora Petrakovskaja Louis HennetDominique Thiaudière Marie-Louise Saboungi 《Journal of magnetism and magnetic materials》2011,323(5):451-460
We report electron magnetic resonance (EMR) and magnetooptical studies of borate glasses of molar composition 22.5K2O-22.5Al2O3-55B2O3 co-doped with low concentrations of Fe2O3 and MnO. In as-prepared samples the paramagnetic ions, as a rule, are in diluted state. However, in the case where the ratio of the iron and manganese oxides in the charge is 3/2, magnetic nanoparticles with characteristics close to those of manganese ferrite are formed already at the first stage of the glass preparation, as evidenced by both magnetic circular dichroism (MCD) and EMR. After thermal treatment all glasses show characteristic MCD and EMR spectra, attesting to the presence of magnetic nanoparticles, predominantly including iron ions. Preliminary EXAFS measurements at the Fe K-absorption edge show an emergence of nanoparticles with a structure close to MnFe2O4 after annealing the glasses at 560 °C.By computer simulating the EMR spectra at variable temperatures, a superparamagnetic nature of relatively broad size and shape distribution with the average diameter of ca. 3-4 nm. The characteristic temperature-dependent shift of the apparent resonance field is explained by a strong temperature dependence of the magnetic anisotropy in the nanoparticles.The formation of magnetic nanoparticles confers to the potassium-alumina-borate glasses magnetic and magneto-optical properties typical of magnetically ordered substances. At the same time, they remain transparent in a part of the visible and near infrared spectral range and display a high Faraday rotation value. 相似文献
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Archimede Rotondo Giuseppe Bruno Francesco Nicol Giuseppe Tresoldi Santo Di Pietro 《Acta Crystallographica. Section C, Structural Chemistry》2010,66(1):o15-o19
The structure of 2,6‐bis(2‐pyridyltsulfanylmethyl)pyridine (pytmp), (I), C17H15N3S2, presents a twisted conformation, with the three planar moieties almost perpendicular to each other. The structures of two related derivatives, namely 2,6‐bis(6‐methyl‐2‐pyridylsulfanylmethyl)pyridine (mpytmp), (II), C19H19N3S2, and 2,6‐bis(4‐methyl‐2‐pyrimidylsulfanylmethyl)pyridine (mprtmp) n‐pentane hemisolvate, (III), C17H17N5S2·0.5C5H12, present extended planar fragments with just one quasi‐perpendicular arylsulfanylmethyl side arm, such that the molecules are folded in an L‐shaped conformation. All three conformations appear different from those adopted by similar compounds, demonstrating the great flexibility of such species, although such differences in conformational behaviour might drive specific coordination modes. 相似文献
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Hélène Esnault 《K-Theory》1992,6(1):45-56
On a smooth varietyX defined over a fieldK of characteristic zero, one defines characteristic classes of bundles with an integrableK-connection in a group lifting the Chow group, which map, whenK is the field of complex numbers andX is proper, to Cheeger-Simons' secondary analytic invariants, compatibly with the cycle map in the Deligne cohomology. 相似文献
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