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Abstract

Phone: þ351 234 378 117, Fax: þ351 234 378 197Nanosized single-phase powders of the ferrimagnetic double perovskite Sr 2 FeMoO 6-d (SFMO) with various degrees of the superstructural ordering of the Fe 3þ and Mo 5þ cations have been synthesized by the citrate-gel method at pH ¼ 4, 6, 9 (samples SFMO 4,6,and 9). According to the results of the X-ray photoelectron spectroscopy, a mixed valence state of the iron and molybdenum cations is realized in the obtained SFMO powders, whereby the concentration of Fe 2þ increases and that of Fe 3þ decreases with increasing pH. The charge state of iron and the redistribution of the electron density in SFMO has been studied by means of the M€ ossbauer spectroscopy. The charge disproportionation for the powders obtained at pH ¼ 6 and 9 facilitates the segregation of a-Fe. The temperature dependences of the magnetization measured in the field cooling and zero-field cooling regimes indicate the existence of superparamagnetism in the nanosized grains of SFMO 4, 6, and 9 at T < 19 K. The superparamagnetism is metastable up to a temperature Т S . The applied magnetic field stimulates the transition in nanosized grains from the metastable superparamagnetic state into the stable one, above some value of the magnetic field induction exceeding the minimal anisotropy field. 57Fe M€ ossbauer spectra taken at 20 K of Sr 2 FeMoO 6-d prepared at pH ¼ 6.

A study of magnetotransport in the n-Si/SiO 2 /Ni nanostructures with granular Ni nanorods in SiO 2 pores was performed over the temperature range 2-300 K and at the magnetic fields induction up to 8 T. The n-Si/ SiO 2 /Ni Schottky nanostructures display the enhanced magnetoresistive effect at 25 K due to the impurity avalanche mechanism.

Self-organized silver nanostructures were grown in porous Si/SiO 2 matrix fabricated by ion track technology. The different silver nanostructures with shapes like "sunflowers", "azalea" or "corn" were realized by applying wet-chemical electroless deposition. We show that reproducible self-organized silver "sunflower" like nanostructures provide a high enhanced Raman signal of Nile blue dye molecules. Signal enhancement for a few or even just a single silver "sunflower" is demonstrated by analyzing the surface-enhanced Raman signature of Nile blue dye molecules. According to this, the silver nanostructures can act as efficient surfaces for surface enhanced Raman spectroscopy as well as (bio)-sensor applications.