The possibility of producing valued devices from low cost natural resources is a subject of broad interest. The present study explores the preparation and characterization of silk fibroin dense membranes using waste silk fibers from textile processing. Morphology, crystallinity, thermal resistance and cytotoxicity of membranes as well as the changes on the secondary structure of silk fibroin were analyzed after undergoing treatment with ethanol. Membranes presented amorphous patterns as determined via X-ray diffraction. The secondary structure of silk fibroin on dense membranes was either random coil (silk I) or beta-sheet (silk II), before and after ethanol treatment, respectively. The sterilized membranes presented no cytotoxicity to endothelial cells during in vitro assays. This fact stresses the material potential to be used in the fabrication of biomaterials, as coatings of cardiovascular devices and as membranes for wound dressing or drug delivery systems.

The spin-and orbital-moment magnetization form factors in NiO have been measured using magnetic x-ray scattering. The polarization analysis of nonresonant magnetic-scattering intensities has evidenced a large contribution from the orbital moment to the total magnetization. In the antiferromagnetic phase, the orbital moment contributes 17Ϯ3% to the magnetization density. ͓S0163-1829͑98͒05313-2͔

In this work the physical properties of the intermetallic compound TbRhIn 5 were investigated by means of temperature-dependent magnetic susceptibility, electrical resistivity, heat-capacity, and resonant x-ray magnetic diffraction experiments. TbRhIn 5 is an intermetallic compound that orders antiferromagnetically at T N = 45.5 K, the highest ordering temperature among the existing RRhIn 5 ͑1-1-5, R = rare earth͒ materials, which in contrast to what is expected from a de Gennes scaling along the RRhIn 5 series. The x-ray resonant diffraction data have allowed us to solve the magnetic structure of TbRhIn 5 . Below T N , we found a commensurate antiferromagnetic structure with a propagation vector ͑1/2,0,1/2͒ and the Tb moments oriented along the c axis. Strong ͑over two orders of magnitude͒ dipolar enhancements of the magnetic Bragg peaks were observed at both Tb absorption edges L II and L III , indicating a fairly high polarization of the Tb 5d levels. Using a mean-field model including an isotropic first-neighbor exchange interaction ͑J R-R ͒ and the tetragonal crystalline electrical field ͑CEF͒, we evaluate the influence of the CEF effects in the physical properties of TbRhIn 5 . The results reported here seem to corroborate a general trend of CEF-driven effects on T N along the RRhIn 5 series.

We discuss the evolution of the magnetic properties and magnetic structures along the series of intermetallic compounds RmMIn3m+2 (R=Ce, Nd, Gd, Tb; M=Rh, Ir; and m=1,2). The m=1,2 are, respectively, the single layer and bilayer tetragonal derivatives of their cubic RIn3 relatives. Using a mean field model including an isotropic first-neighbors Ruderman-Kittel-Kasuya-Yoshida interaction (K) and the tetragonal crystalline electrical field (CEF), we demonstrated that, for realistic values of K and CEF parameters, one can qualitatively describe the direction of the ordered moments and the behavior of the ordering temperature for these series. The particular case, where the rare-earth ordered moments lie in the ab plane or are tilted from the c axis and TN can be reduced by tuning the CEF parameters, revealed an interesting kind of frustration that may be relevant to the physical properties of complex classes of materials such as the RmMIn3m+2 (M=Rh, Ir, and Co; m=1,2) heavy-fermion superconductors.

Resonant x-ray diffraction measurements on Gd 2 IrIn 8 reveal an antiferromagnetic structure below T N ϭ40.8 K with wave vector ϭ(1 2 ,0,0) and the Gd moments lying in the tetragonal ab plane, indicating partly frustrated exchange interactions. Strong ͑over three orders of magnitude͒ dipolar resonant enhancements of the magnetic reflections were observed at both Gd L II and L III edges, indicating a relatively high magnetic polarization of the Gd 5d levels. Three-dimensional magnetic fluctuations are evidenced below T N , while measurements taken slightly above T N are consistent with two coexisting length scales for the magnetic correlations. Implications of these results for the physics of Ce n M m In 3nϩ2m (M ϭCo, Rh, or Ir͒ heavy-fermion superconductors are discussed.

Phase transitions of the ionic liquids n-butyl-trimethylammonium bis(trifluoromethanesulfonyl)imide, [N1114][NTf2], and methyl-tributylammonium bis(trifluoromethanesulfonyl)imide, [N1444][NTf2], were investigated by differential scanning calorimetry (DSC), X-ray diffraction (XRD) measurements, and Raman spectroscopy. XRD and Raman spectra were obtained as a function of temperature at atmospheric pressure, and also under high pressure at room temperature using a diamond anvil cell (DAC). [N1444][NTf2] experiences glass transition at low temperature, whereas [N1114][NTf2] crystallizes or not depending on the cooling rate. Both the ionic liquids exhibit glass transition under high pressure. XRD and low-frequency Raman spectra provide a consistent physical picture of structural ordering-disordering accompanying the thermal events of crystallization, glass transition, cold crystallization, pre-melting, and melting. Raman spectra in the high-frequency range of some specific cation and anion normal modes reveal conformational changes of the molecular structures along phase transitions.

Electron spin resonance ͑ESR͒ experiments at different fields or frequencies ͑4.1Յ Յ 34.4 GHz͒ in the Kondo lattice ͑T K Ӎ 25 K͒ YbRh 2 Si 2 single-crystal compounds confirmed the observation of a single anisotropic Dysonian resonance with g Ќc Х 3.55 and no hyperfine components for 4.2Շ T Շ 20 K. However, our studies differently reveal that ͑i͒ the ESR spectra for H Ќc show strong-field-dependent spin-lattice relaxation, ͑ii͒ a weak-field and temperature-dependent effective g value, ͑iii͒ a dramatic suppression of the ESR intensity beyond 15% of Lu doping, and ͑iv͒ a strong sample and Lu-doping ͑Յ15%͒ dependence of the ESR data. These results suggest a different scenario where the ESR signal may be associated to a coupled Yb 3+ -conduction electron resonant collective mode with a strong bottleneck and dynamiclike behavior.

No abstract