Synthesis and magnetic properties of cobalt ferrite nanoparticles in polycarbosilane ceramic matrix

Synthesis and magnetic properties of cobalt ferrite nanoparticles in polycarbosilane ceramic matrix. Yurkov G.Y., Shashkeev K.A., Kondrashov S.V., Popkov O.V., Shcherbakova G.I., Zhigalov D.V., Pankratov D.A., Ovchenkov E.A., Koksharov Yu.A. //Journal of Alloys and Compounds. 2016. V.686. P.421–430

Composite materials comprised of a ceramic matrix with metal-containing nanoparticles were prepared by sintering a blend of cobalt ferrite nanoparticles and polycarbosilane. Sintering process was performed either in air or argon, resulting in different material composition. The air-sintering materials consist mainly of oxide phases (silica matrix and cobalt ferrite nanoparticles). The process of sintering in argon leads to partial reduction of oxides and formation of α-Fe, carbide and silicate phases. The prepared samples were characterized by the SEM, TEM, XRD and EMR techniques and the Mössbauer spectroscopy. Static magnetic properties were also studied. All samples were found to be soft magnetic. Sintering, especially in argon, increases remnant magnetization of resulting composite products.

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Mössbauer study of oxo derivatives of iron in the Fe2O3-Na2O2 system

Mössbauer study of oxo derivatives of iron in the Fe₂O₃-Na₂O₂ system. Pankratov D.A. //Inorganic Materials. 2014. V. 50. № 1. P. 82-89

Various compositions of oxo derivatives of iron reacting with sodium peroxide have been studied by Mössbauer spectroscopy. We have examined several mathematical models of the measured spectra. The results obtained are inconsistent with hypotheses made previously that such conditions may lead to the formation of compounds of iron in oxidation states above (+6). We demonstrate that a large excess of an alkali peroxide leads, most likely, to the formation of at least two iron(V) derivatives in tetrahedral coordination. In their Mössbauer spectra, they have isomer shifts of −0.45 and −0.51 mm/s and unusually large quadrupole splittings: 1.32 and 1.94 mm/s (at room temperature).

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Potassium hexahydroperoxostannate: synthesis and structure

Potassium hexahydroperoxostannate: synthesis and structure. Ippolitov E.G., Tripol'skaya T.A., Prikhodchenko P.V., Pankratov D.A. //Russian Journal of Inorganic Chemistry. 2001. V.46. №6. P.851-857

Polycrystalline potassium hexahydroperoxostannate was prepared by replacement of hydroxo groups in potassium hexahydroxostannate upon its dissolution in hydrogen peroxide. A comparative study of the product and the starting hydroxostannate by powder X-ray diffraction analysis, thermogravimetry, and IR, ²H, ³⁹K, and ¹¹⁹Sn NMR, and Mössbauer spectroscopy was carried out. The peroxo compound K₂Sn(OOH)₆ crystallizes in the hexagonal system with a = 7.264(7) Å, c = 10.168(4) Å. IR, NMR, and Mössbauer spectroscopy data show that the tin coordination polyhedron in the peroxo compound is an octahedron formed by the coordinated hydroperoxo groups.

Previously, sodium hexahydroperoxostannate was prepared and characterized by powder X-ray diffraction analysis, thermogravimetry, IR, ¹H NMR, and Mossbauer spectroscopy, and by thermodynamic and kinetic method. The tin atom in this compound were found to occur in the octahedral environment of hydroperoxo group. It appeared pertinent to confirm the possibility of formation of this type of tin compound by preparing a new hydroperoxo complex. To this end, we performed the first synthesis of potassium hexahydroperoxostannate. Comparative study of potassium hexahydrosstannate (1) and hexahydroperoxosstannate (2) and their deuterated analogue (1a and 2a, respectively) was carried out by powder X-ray diffraction analysis, thermogravimetry, and IR, NMR (²H, ³⁹K and ¹¹⁹Sn), and Mossbauer spectroscopy.

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Electron paramagnetic resonance spectra near the spin-glass transition in iron oxide nanoparticles

Electron paramagnetic resonance spectra near the spin-glass transition in iron oxide nanoparticles. Koksharov Yu.A., Gubin S.P., Kosobudsky I.D., Yurkov G.Yu., Pankratov D.A., Ponomarenko L.A., Mikheev M.G., Beltran M., Khodorkovsky Y., Tishin A.M. //Physical Review B: Condensed Matter and Materials Physics. 2001. V. 63. № 1. P. 124071-124074

Electron paramagnetic resonance (EPR) in iron-oxide nanoparticles (∼ 2.5 nm) embedded in a polyethylene matrix reveals the sharp line broadening and the resonance field shift on sample cooling below T_F ≈ 40 K. At the same temperature a distinct anomaly in the field-cooled magnetization is detected. The temperature dependences of EPR parameters below T_F are definitely different than those found for various nanoparticles in the superparamagnetic regime. In contrast to canonical bulk spin glasses, a linear fall-off of the EPR linewidth is observed. Such behavior can be explained in terms of the random-field model of exchange anisotropy.

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