Tatiana Yu. Kiseleva

Mechanochemically induced formation of amorphous phase at oxide nanocomposite interfaces

α-Fe2O3-Fe mixtures of different compositions ground in high energy ball mill were studied. The formation of amorphous iron-based magnetic phase was detected by means of Mossbauer spectroscopy and magnetic measurements. The amount of this phase increases with Fe/α-Fe2O3 ratio in starting mixtures increase. Its thermal stability was studied by means of magnetic and DCS measurements.

Iron-Based Amorphous Magnetic Phase Formation in the Course of Fe and Fe2O3 Mechanical Activation

Solid phase high energy mechanochemical interaction of α-Fe2O3(hematite) and Fe in powder mixture have been studied. The formation of amorphous iron-based magnetic phase in this process was detected by means of Mossbauer spectroscopy and magnetic measurements. The amount of this phase increases with Fe addition in reduced mixture. Its thermal stability have been studied by magnetic and DCS measurements at constant α-Fe2O3 and gradually increased Fe concentrations.

Oriented arrays of iron nanowires: synthesis, structural and magnetic aspects

Iron nanowires with the diameter of ca. 40 nm and a length up to few dozens of microns are fabricated via templated electrodeposition using anodic aluminum oxide (AAO) film as porous matrix. Despite polycrystalline structure of wires the technique allows fabrication of dense deposits with micrometer-sized single crystalline grains within AAO templates and high chemical stability towards oxidation. Nanowire arrays exhibit strong magnetization anisotropy with saturation magnetization of 180 emu/g and coercive field of 815 Oe in direction parallel to the long axis of nanowires and 230 Oe in perpendicular direction. The effective hyperfine fields on iron atoms as extracted from Mossbauer and Nuclear Forward Scattering of sample in demagnetized state indicates slight deviation of magnetization vector (~ 6°) from nanowire long axis appearing probably due to curling of magnetic moments by antisymmetric exchange interactions at the surface of nanowires.Graphical Abstract

Comparative study of thermal degradation of iron-sulfur proteins in spinach chloroplasts and membranes of thermophilic cyanobacteria: mössbauer spectroscopy

Mössbauer spectra of chloroplasts isolated from spinach plants grown in a mineral medium enriched with 57Fe and Mössbauer spectra of native membranes of the thermophilic cyanobacterium Synechococcus elongatus contain a broad asymmetric doublet typical of the iron–sulfur proteins of Photosystem (PS) I. Exposure of chloroplasts to temperatures of 20-70°C significantly modifies the central part of the spectra. This spectral change is evidence of decreased magnitude of the quadrupole splitting. However, the thermally induced doublet (ΔQ = 3.10 mm/sec and δ = 1.28 mm/sec) typical of hydrated forms of reduced (divalent) inorganic iron is not observed in spinach chloroplasts. This doublet is usually associated with degradation of active centers of ferredoxin, a surface-exposed protein of PS I. The Mössbauer spectra of photosynthetic membranes of spinach chloroplasts and cyanobacteria were compared using the probability distribution function of quadrupole shift (1/2 quadrupole splitting ΔQ) of trivalent iron. The results of calculation of these functions for the two preparations showed that upon increasing the heating temperature there was a decrease in the probability of the presence of native iron–sulfur centers FX, FA, and FB (quadrupole shift range, 0.43-0.67 mm/sec) in heated preparations. This process was also accompanied by an increase in the probability of appearance of clusters of trivalent iron. This increase was found to be either gradual and continuous or abrupt and discrete in photosynthetic membranes of cyanobacteria or spinach chloroplasts, respectively. The probability of the presence of the iron–sulfur centers FX, FA, and FB in chloroplasts abruptly decreases to virtually to zero within the temperature range critical for inhibition of electron transport through PS I to oxygen. In cyanobacteria, both thermal destruction of iron–sulfur centers of PS I and functional degradation of PS I are shifted toward a higher temperature. The results of this study suggest that the same mechanism of thermal destruction of the PS I core occurs in both thermophilic and mesophilic organisms: destruction of iron–sulfur centers FX, FA, and FB, release of oxidized (trivalent) iron, and its accumulation in membrane-bound iron-oxo clusters.

Amorphous Shell Formation on the Iron Particles during Mechanosynthesis in Fe2O3/Fe/(Ga,Al) Mixtures

Amorphous shell formation on the Fe-particles surface in course of mechanochemical nanocomposite synthesis in Fe2O3+Fe, Fe2O3+Al+Fe, and Fe2O3+Ga+Fe powders mixtures have been observed by Mössbauer spectroscopy and magnetic measurements.

The formation of Fe–Ga–In nanocomposite particles using mechanochemical interaction of Fe with the Ga–In eutectic

Mechanochemical interaction of Fe powder with the liquid Ga–In eutectic in the Fe-rich concentration corner of the Fe–Ga–In phase diagram was studied and compared with binary Fe–Ga and Fe–In specimens. Slow formation of diluted solid solutions in the Fe–In system was confirmed. In the Fe–Ga system, the dominant concentrated A2 solid solution is formed with Heff = 236 kOe, accompanied by ordered D03 and L12 phases. The Fe–Ga–In system features a stationary equilibrium between the concentrated A2 phase and D03 in the iron matrix.

Magnetodeformational Anisotropy of FeGa/PU Hybrid Nanocomposite via Particle Concentration and Spatial Orientation

The present work has been undertaken to research effects of structure, morphology, volume fraction, spatial arrangement of magnetostrictive intermetallic FeGa alloy particles dispersed in modified polyurethane matrix. Correlation of composite magnetic behavior with structure and mechanical properties has been obtained by measurements of magnetostriction, remanent magnetization anisotropy, SEM, and dynamical mechanical analysis. Anisotropic chain structures of magnetic particles within the polymer with different interparticle interactions were observed. The increase of the magnetostrictive response with tailor-made magnetic anisotropy induced by magnetic particles volume fraction has been demonstrated

Magnetic Properties and Thermal Stability of xFe (100-x)SiO2 (x=5-95) Powder Nanocomposites

The study of Fe/SiO2 nanocomposites magnetic properties and structure relationships was performed in dependence on Fe to SiO2 relative concentration and type of precursors preparation (mechanical mixing or ultrasonic homogenization). Thermal metallization method in hot hydrogen of initial reagents [хFeOOH and (100-x)SiO2] was applied for nanocermets production. It was determined that formation of air-tight shell on the particles surface affects the nanocomposites magnetization values and their air temperature stability.