D. A. Pankratov

Electron paramagnetic resonance of ferrite nanoparticles

Three types of iron-based oxide nanoparticles (weight compositions Fe2O3, BaFe2O4, and BaFe12O19) embedded in a polyethylene matrix are studied using the electron paramagnetic resonance technique. All nanoparticles are found to be multiphase. Thermal variations of electron paramagnetic resonance spectra reveal the presence of two phases in the Fe2O3 nanoparticles. One such phase undergoes an antiferromagnetic-like transition near 6 K. Nanoparticles of BaFe2O4 demonstrate a resonance anomaly near 125 K that could indicate the presence of a magnetic phase. Reduced magnetic anisotropy in BaFe12O19 nanoparticles may be related to either structural imperfection or particle smallness (effective diameter of less than 10 nm). Our data clearly show that low temperature experiments are desirable for the correct identification of nanoparticles by means of the electron paramagnetic resonance technique.

Iron(III) Oxide Nanoparticles in a Polyethylene Matrix

A method is proposed for the preparation of iron(III) oxide nanoparticles via thermal decomposition of iron(III) acetate in a high-temperature solution of polyethylene. The nanoparticles were characterized by EXAFS, EPR, and Mössbauer spectroscopy. The nearest neighbor environment of Fe in the nanoparticles was shown to be similar to that in the structure of γ-Fe2O3 . According to the Mössbauer results, the material contains iron(III) oxide in superparamagnetic and ferromagnetic states similar to γ-Fe2O3 . The particle size determined by high-resolution transmission electron microscopy is consistent with x-ray diffraction data. Experimental data are presented on the field-dependent magnetization of the material.

Constrained growth of anisotropic magnetic δ-FeOOH nanoparticles in the presence of humic substances

Natural polyelectrolytes, humic substances, are suggested to control in situ growth of feroxyhyte nanoparticles of a highly reduced mean size and with enhanced colloidal stability in salt solutions. The feroxyhyte is formed as 2–5 nm thick and 20 × 20 nm wide nanoflakes due to the blocking of developing facets of feroxyhyte and constraints caused by diffusion limitations of ionic constituents across partially charged branches of humic substances.

EPR spectroscopy of transformations of iridium(III) and iridium(IV) hydroxo complexes in alkaline media

Processes that occur in strong alkaline solutions of iridium(III) and iridium(IV) hydroxo complexes have been studied by EPR and electronic absorption spectroscopy. It has been demonstrated that dissolution of iridium compounds in alkaline solutions should be accompanied by a series of complicated transformations involving oxygen, which lead to the formation of several binuclear iridium(III, III), (III, IV), and (IV, IV) dioxygen complexes.

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

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).

Structural features of green cobalt(III) hydroxide

Emission Mössbauer and X-ray absorption XANES/EXAFS spectroscopic techniques are applied to elucidate the structural features of green cobalt(III) hydroxide. A comparative analysis of structurally characterized cobalt(II) and cobalt(III) oxo-compounds shows that the parameters of the local environment of cobalt atoms in green cobalt(III) hydroxide differ substantially from those of its analogues.

Ab Initio Calculations of Hydroxoplatinum Compounds: II. Binuclear Platinum(IV) Superoxo Complexes

The structural and spectral data have been obtained by ab initio methods for the [(OH)4Pt(μ-O2)(μ- OH)Pt(OH)4]2−, [(OH)4Pt(μ-O2)(μ-OH)Pt(OH)4(OH)]3−, [(OH)5Pt(μ-O2)Pt(OH)5]3−, and [(H2O)(OH)4Pt(μ- O2)Pt(OH)4(H2O)]- clusters, corresponding to binuclear platinum(IV) superoxo complexes with one and two bridges. The data obtained are in good agreement with experimental data and make it possible to judge the structure of available complexes.

Anisotropic magnetic hyperfine interactions in phosphide FeP

The results from a Mössbauer study of 57Fe Mössbauer nuclei in binary phosphide FeP, which has an unusual magnetic structure, are presented. Model decoding of the Mössbauer spectra is performed with allowance for features of the crystal structure of this compound, using data on its spin-modulated magnetic ordering. A proposed model expansion of the spectra allows us to describe consistently Mössbauer data obtained over a wide range of temperatures that includes the magnetic phase transition point. Possible explanations are offered for the low magnitude and spatial anisotropy of hyperfine magnetic field Hhf on 57Fe nuclei.

Synthesis and physicochemical properties of composites for electromagnetic shielding applications: a polymeric matrix impregnated with iron- or cobalt-containing nanoparticles

Abstract. Magnetic, magnetic resonance, and structural properties of iron and cobalt nanoparticles embedded in a polyethylene matrix were studied. The materials were prepared by thermal decomposition of cobalt or iron formate in a polyethylene melt in mineral oil and contained from 2 to 40% wt. of metal. Transmission electron microscopy data indicate that the average diameter of particles is up to 8.0 nm. According to extended x-ray absorption fine structure and Mössbauer spectroscopy studies, the particles comprise a metallic core and nonmetallic shell which is chemically bound to the surrounding matrix. Electrophysical and magnetic properties of the materials prepared were studied along with their reflection and attenuation factors in the super high frequency band. The materials were found to be suitable for use in electromagnetic shielding.

Coprecipitation of iron and platinum(IV) hydroxo complexes as probed by Mössbauer spectroscopy

Stabilization of 57Fe compounds in matrices of solid solutions of platinum(IV) superoxo- and hydroxo complexes was probed by Mössbauer spectroscopy. The ratio FeIII/FeIV in these matrices is 20/1.