V. K. Imshennik

Magnetic phase transitions in nanostructures with different cluster orderings

Nanostructures have been synthesized by (i) the micellar template method with the subsequent organization of Fe2O3 nanoclusters about 10 nm in size to a cluster crystal and (ii) by the aerosol method with the fixation of Fe2O3 nanoclusters about 10 nm in size in the NaCl matrix. The magnetic properties of the synthesized nanostructures have been studied. The Mössbauer spectroscopic examination of the cluster crystal revealed a magnetic phase transition of the first order, with the transition temperature being near the room temperature. This nanostructure is characterized by a steep magnetization curve, which is typical of an ordered structure with a weak intercluster interaction like a molecular crystal and a low energy of the magnetic anisotropy K = 3.5 × 104 J/m3. The disordered Fe2O3 nanostructure in the NaCl matrix is characterized by superparamagnetic behavior and smooth magnetization curves without saturation at 1 T and the magnetic anisotropy energy K = 2.5 × 104 J/m3, which is close to the corresponding value in bulk α- and γ-Fe2O3.

The formation and properties of one-dimensional FeHal2 (Hal = Cl, Br, I) nanocrystals in channels of single-walled carbon nanotubes

FeCl2@OCHT, FeBr2@OCHT, and FeI2@OCHT nanocomposites were obtained by capillary filling of the channels of carbon single-walled nanotubes (SWNTs) with melts of iron halogenides. The composites were studied by high resolution transmission electron microscopy (HRTEM), the capillary condensation of nitrogen at 77K, Raman spectroscopy, optical absorption spectroscopy, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and Moessbauer spectroscopy. Substantial distinctions in the combination scattering spectra of SWNTs and nanocomposites in the region of radial modes and in the region of longitudinal and tangential oscillations were revealed. The presence of electron transfer between the nanocrystal and the SWNT wall was established in the nanocomposites. For the FeCl2@OCHT nanocomposite, two states of Fe+2 were found: the first is characterized by electron transfer from the nanotube to the nanocrystal, which leads to the electron structure of the SWNT and FeCl2 changing; the second corresponds to the strained intercalated state resulting from the mechanical effect of the small SWNT diameter on the FeCl2 nanocrystal.

Magnetic nanostructures based on nanoclusters of iron oxides

Using magnetization and Mössbauer spectroscopy, investigations of the magnetic properties of α-Fe2O3-SiO2 and γ-Fe2O3-SiO2 nanostructures, including α-Fe2O3 nanoclusters 2 nm in size and γ-Fe2O3 nanoclusters 3–4 nm in size in silica gel pores, have been conducted. For α-Fe2O3-SiO2 nanostructures, magnetic phase transitions of the first order are detected and examined with the transition temperature dependent on the nanocluster size and intercluster interactions. α-Fe2O3 nanoclusters up to 16 K remain in the noncompensated antiferromagnetic state (upper Morin point temperature). At low temperatures, α-Fe2O3 nanoclusters reveal quantum-size effects. For γ-Fe2O3-SiO2 nanostructures, supermagnetic behavior with a blocking point dependent on intercluster interactions is typical. At low temperatures, intercluster interactions lead to the appearance of a coercive force of 0.03 T.

Microstructure and gas-sensing properties of nanocrystalline NiFe2O4 prepared by spray pyrolysis

Nanocrystalline nickel ferrite with a crystallite size from 3 to 40 nm has been prepared by spray pyrolysis. The 57Fe Mössbauer spectrum of NiFe2O4 samples has been found to vary systematically with crystallite size. The sensing response of the nanocrystalline nickel ferrite to 50 ppm NH3 has been studied using in situ conductance measurements. NiFe2O4 offers a strong sensing response to ammonia at the level of its maximum concentration limit. The optimum nickel ferrite crystallite size and temperature for ammonia detection are determined.

X-ray photoelectron and Mössbauer spectroscopy studies of bimetallic 57Fe-Pd nanocomposites prepared by metal-vapor synthesis

X-ray photoelectron and Mössbauer spectroscopy were used to study the composition and structure of 57Fe-Pd bimetallic black and 57Fe-Pd/SiO2 nanocomposites prepared by metal-vapor synthesis. The main parameters of the core level photoelectron spectra of 57Fe-Pd systems were determined. The bimetallic system was shown to be a disordered amorphous structure consisting of Pd particles, superparamagnetic γ-Fe2O3 nanoparticles with size 8–10 nm, and a Fe-O-Pd solid solution. Considerable broadening of Pd 3d peaks in 57Fe-Pd/SiO2 and an increase in the O 1s-Si 2p energy interval by 0.4 eV with respect to the spectrum of initial SiO2 were observed; this was evidence of the interaction of Pd with the support. The binding energy of Fe 2p3/2 peak in the nanocomposite spectrum was close to that of Fe2O3, but had a smaller width of the satellite peak and a larger spin-orbit splitting, which was indicative of a considerable amount of FeOOH on the surface compared with the other iron oxides.

Magnetic properties of ultrasmall iron oxide nanoclusters in a polymer matrix

The synthesis of iron oxide nanoclusters in the matrix of an interpolyelectrolyte complex based on poly(acrylic acid) and polyethylenimine is described. The effect of the method of cluster formation (by the oxidation or reduction of iron ions) on the magnetic properties of polymer nanocomposites was studied. The influence of the surface modification of iron oxide nanoclusters in a polymer matrix on the interaction of the nanoclusters with the matrix, the appearance of first-order phase transitions, and the disappearance of superparamagnetism were examined. Mössbauer spectroscopy and magnetization measurements were used for identifying first-order magnetic phase transitions or superparamagnetism.

Metal-containing systems based on chitosan and a collagen-chitosan composite

Metal-carrying polysaccharides based on chitosan and a collagen-chitosan composite (collachit) were obtained by modifying polymers by Au and Fe nanoparticles, which were prepared via metal vapor synthesis. Gold nanoparticles were synthesized using organosols with triethylamine; Fe nanoparticles, using the thermally labile bis(arene) complex, viz., bis(toluene)iron. The composition and structures of the resulting materials were studied by Mössbauer spectroscopy, XPS, and X-ray diagnostics using synchrotron radiation. Particles of Au (7.5–10 nm) and Fe (6–7 nm) were detected in metallopolymers by X-ray powder diffraction. The XPS analysis of gold-containing nanocomposites showed two states of Au4f. One of them is metallic with the binding energy of the Au4f7/2 peak equal to 83.8 eV, and another one is partially oxidized with the binding energy of the Au4f7/2 peak equal to 85.5 eV; the atomic concentrations of the two states are 16% and 84%, respectively. A comparative analysis of the Mössbauer spectra of iron-containing chitosan and collachit demonstrated that these two samples have similar structures. Thus, iron is present as a metallic phase (−30%) and a superparamagnetic gamma-iron oxide (−74%). The size of gamma-iron oxide nanoclusters in the samples can be estimated at −6–8 nm.

The local structure of TiO2-based nanotubes intercalated with iron (III)

Transmission electron microscopy, X-ray photoelectron spectroscopy, and 57Fe Mössbauer spectroscopy have been used to study TiO2-based nanotubes (TNTs) intercalated with 57Fe. A structural model of doped TNTs has been proposed that includes TNTs in the form of a “scroll” with nonmagnetic Fe-O-Fe layers spaced at ∼0.7-nm intervals in the interlayer spacing and ∼20-nm iron oxide clusters on the outer surface of the TNTs.

New approach to the synthesis of polynuclear heterometallic pivalates with iron and manganese atoms

New hexanuclear Fe(III)–Mn(II, III) pivalates [Fe2III Mn4II(O)2(Piv)10(HPiv)4] (I) or [Fe4III Mn2III(O)2(Piv)12(CH2O2)(HPiv)2] · Et2O (II) are synthesized using the solid-state thermolysis of [Fe2Mn(O)(Piv)6(HPiv)3] (90°С). Complexes I and II differ by the ratio of iron and manganese ions, which depends on the atmospheric composition during thermolysis. The structures of compounds I and II are determined by X-ray diffraction studies. According to the parameters of the Mössbauer spectrum, complex I contains the Fe3+ ions in the high-spin state in the octahedral environment of oxygen atoms.

The synthesis of doxorubicin-conjugated magnetite nanoparticles and their magnetic resonance and cytotoxic properties

The possibility of increasing the effectiveness of antitumor drugs such as doxorubicin by preparing its complex with ultrafine magnetic iron oxide nanoparticles is considered. A method for binding doxorubicin molecules to magnetic nanoparticles via citric acid is proposed. The main magnetic properties of the obtained conjugates were studied by proton relaxometry and Mössbauer spectroscopy, while their cytotoxic activity was evaluated via spectrophotometric MTT assay in HeLa cells. It was shown that the conjugates of magnetite nanoparticles with doxorubicin are characterized by a high level of contrast in magnetic resonance imaging. The magnetic properties of doxorubicin-free and bound magnetite nanoparticles are mainly determined by the average size of nanoobjects and the phase composition and slightly depend on the composition of the stabilizing shell. The cytotoxic effect of the synthesized conjugates of magnetite nanoparticles with doxorubicin is higher than that of unbound doxorubicin. This makes it possible to increase the antitumor effect of doxorubicin and control the dynamics of its delivery in the form of a conjugate into the disease focus due to the magnetic contrast properties of nanoparticles.