I.V. Shchetinin

Nanoscale engineering of hybrid magnetite–carbon nanofibre materials for magnetic resonance imaging contrast agents

Magnetic nanomaterials show significant promise as contrast agents for magnetic resonance imaging (MRI). We have developed a new highly efficient one-step procedure for the synthesis of magnetically- functionalised hollow carbon nanofibres, where (i) the carbon nanofibres act as both a template and a support for the nucleation and growth of magnetite nanoparticles and (ii) the structural (size, dispersity and morphology) and functional (magnetisation and coercivity) properties of the magnetic nanoparticles formed on nanofibres are strictly controlled by the mass ratio of the magnetite precursor to the nanofibres and the solvent employed during synthesis. We have shown that our magnetite-nanofibre materials are effectively solubilised in water resulting in a stable suspension that has been employed as a ‘‘negative’’ MRI contrast agent with an excellent transverse relaxivity (r2) of (268 13) mM s 1, surpassing current commercial materials and state-of-the-art magnetic nanoscale platforms in performance for MRI contrast at high magnetic fields. The preparation and evaluation of this unique hybrid nanomaterial represents a critical step towards the realisation of a highly efficient ‘‘smart’’ MRI theranostic agent – a material that allows for the combined diagnosis (with MRI), treatment (with magnetic targeting) and follow-up of a disease (with MRI) – currently in high demand for various clinical applications, including stratified nanomedicine.

XMCD study of the local magnetic and structural properties of microcrystalline NdFeB-based alloys

X-ray Magnetic Circular Dichroism (XMCD) technique was used to investigate local magnetic properties of microcrystalline Nd10.4Zr4.0Fe79.2B6.4 samples, oriented along either easy or hard magnetization direction. The Nd L2,3 and Fe K edge XMCD spectra were measured at room temperature under a magnetic field of T. A very strong dependence of XMCD spectra on the sample orientation has been observed at the NdL2,3-edges, whereas the Fe K-edge XMCD spectra are found to be practically isotropic. This result indicates that magnetic anisotropy of NdFeB-based alloys originates from the Nd sublattice. In addition, element selective magnetization curves have been recorded by measuring the intensity of XMCD signals as a function of an applied magnetic field up to T. To find a correlation between local and macroscopic magnetic properties of studied samples we compared these data with magnetization curves, measured by vibrating sample magnetometer up to T. Results are important for understanding the origin of high-coercivity state in NdFeB-based intermetallic compounds.

Microstructure and Magnetic Properties of Melt-Spun Nd-Rich Nd-Fe Alloys

The effect of composition on the magnetic properties and microstructure of Nd-rich Nd-Fe alloys prepared by melt-spinning were investigated. Several magnetic phases with ordering temperatures at about 10, 37, 48, and 420-480 K were detected from the temperature dependence of magnetization. The first transition is due to the presence of the double-hexagonal-close-packed Nd phase. The magnetic transitions at 37 and 48 K may be related to the face-centered-cubic Nd-based phase and the Nd-rich nanocrystals. The high-temperature ferromagnetic-paramagnetic transitions at 420-480 K may be connected with the amorphous-like Fe-Nd phase enriched in Fe, which is observed by transmission electron microscopy in the intergranular regions. At temperatures below 100 K, the magnetization of the Nd-Fe ribbons did not saturate in a magnetic field as high as 7200 kA/m. The correlations between the microstructure and coercivity of the Nd-rich Nd-Fe ribbons are discussed.

Synthesis of Iron Oxide Nanoclusters by Thermal Decomposition

Herein, we report a novel one-step solvothermal synthesis of magnetite nanoclusters (MNCs). In this report, we discuss the synthesis, structure, and properties of MNCs and contrast enhancement in T2-weighted MR images using magnetite nanoclusters. The effect of different organic acids, used as surfactants, on the size and shape of MNCs was investigated. The structure and properties of samples were determined by magnetic measurements, TGA, TEM, HRTEM, XRD, FTIR, and MRI. Magnetic measurements show that obtained MNCs have relatively high saturation magnetization values (65.1-81.5 emu/g) and dependence of the coercive force on the average size of MNCs was established. MNCs were transferred into an aqueous medium by Pluronic F-127, and T2-relaxivity values were determined. T2-Weighted MR phantom images clearly demonstrated that such magnetite nanoclusters can be used as contrast agents for MRI.

Interaction of hydrogen with the intermetallic compound Nd 2 Fe 17 studied by calorimetry

Interaction of hydrogen with the intermetallic compound Nd2Fe17 has been studied for the first time by calorimetry using a differential heat conduction calorimeter coupled to a Sieverts apparatus. Hydrogen absorption and desorption reactions were run at 200°C, and two types of data were obtained: p–C–T and ΔH–C–T (where p is the equilibrium hydrogen pressure, C = H/Nd2Fe17, ΔH is the reaction enthalpy, and T is the measurement temperature). The p–C–T curves obtained for the hydrogen absorption and desorption processes have no plateau or two-phase region, in contrast to what is characteristic of the formation of a hydride phase. At the same time, the ΔH(C) curves have a few portions where the enthalpy of reaction between hydrogen and the intermetallic compound remains constant: 0 < C < 2.0, with ΔHabs =–85.05 ± 0.65 kJ/mol H2; 2.0 < C < 2.7, with ΔHabs =–80.64 ± 1.00 kJ/mol H2; and 1.9 < C < 2.7, with ΔHdes = 76.48 ± 0.85 kJ/mol H2. The data obtained in this study suggest that positions 9e and 18g in the intermetallic compound are occupied by hydrogen in a particular order.

Investigation of hydrogen interaction with magnetic materials of Nd–Fe–B type by calorimetry method

The interaction of hydrogen with the Nd–Fe–B system is studied via calorimetry with use of a Tian–Calvet differential calorimeter and reconstruction of the pressure–composition isotherms (P–C–T, where Р is the equilibrium pressure of hydrogen, С = H/Nd2Fe14B, and T is the reaction temperature). No hybrid phase coexistence is found on the P–C hydrogen sorption/desorption isotherms or on plots of the dependence of the enthalpy on the hydrogen concentration in the metallic matrix. Nevertheless, several segments with constant enthalpy values can be distinguished in the reaction enthalpy on the hydrogen content plot.

Synthesis and characterization of PEG-silane functionalized iron oxide(II, III) nanoparticles for biomedical application

In this paper we report the synthesis, functionalization, and characterization of ferromagnetic iron oxide (II, III) nanoparticles with different shapes and sizes. Using a number of chemical methods, magnetite nanoparticles having a spherical shape and size of 9 ± 2 nm (coprecipitation), 22 ± 4 nm and 50 ± 6 nm (redox reaction), and 40 ± 5 nm cubes were synthesized. Special attention in this paper is devoted to the covalent modification of magnetite nanoparticles by polymers such as silane-polyethylene glycol (Peg-silane). The main advantage of magnetic nanoparticles modified by polymer is low toxicity, colloidal stability of the prepared magnetite nanoparticles, and the possibility for post functionalization. We determined coercivity and saturated magnetism. Also, the relaxivity T2 was measured by magnetic resonance imaging (MRI). Prepared nanoparticles are of great interest and potential for use in biomedical imaging.

Magnetite-Gold nanohybrids as ideal all-in-one platforms for theranostics

High-quality, 25 nm octahedral-shaped Fe3O4 magnetite nanocrystals are epitaxially grown on 9 nm Au seed nanoparticles using a modified wet-chemical synthesis. These Fe3O4-Au Janus nanoparticles exhibit bulk-like magnetic properties. Due to their high magnetization and octahedral shape, the hybrids show superior in vitro and in vivo T2 relaxivity for magnetic resonance imaging as compared to other types of Fe3O4-Au hybrids and commercial contrast agents. The nanoparticles provide two functional surfaces for theranostic applications. For the first time, Fe3O4-Au hybrids are conjugated with two fluorescent dyes or the combination of drug and dye allowing the simultaneous tracking of the nanoparticle vehicle and the drug cargo in vitro and in vivo. The delivery to tumors and payload release are demonstrated in real time by intravital microscopy. Replacing the dyes by cell-specific molecules and drugs makes the Fe3O4-Au hybrids a unique all-in-one platform for theranostics.

Phase Composition and Magnetic Properties of Nd2Fe14B/α-Fe Nanocomposites Prepared by Mechanical Alloying

Combined studies of hard magnetic Nd2Fe14B/α-Fe nanocomposites are performed. They were prepared by mechanical alloying of melt-quenched Nd7.4Pr2.0Fe76.6Co4.2Zr3.4B6.4 and Nd5.8Fe80Co4.9Ti1.5Si2.5B5.3 alloys taken in mass proportions of 90/10 and 70/30. It is found that, after mechanical alloying, an amorphous–crystalline structure is formed; it consists of the hard magnetic Nd2Fe14B and soft magnetic (amorphous and α-Fe) phases. Subsequent annealing at ~500°C initiates the decomposition of the amorphous phase and the formation of the nanocrystalline Nd2Fe14B and α-Fe phases. This leads to an increase in the coercivity and the residual magnetization-to-saturation magnetization ratio (σr/σs ≥ 0.5). It is assumed that the magnetic hardening of powders is due to the formation of an exchange-coupled state, which results from the exchange interaction between α-Fe nanocrystals and the Nd2Fe14B phase.

Structural and Magnetic Properties of As-Cast Fe–Nd Alloys

The effect of composition on the magnetic properties and microstructure of as-cast Nd–Fe alloys was investigated. The temperature dependence of the hysteresis loops was studied. The magnetic phases with ordering temperatures in the range from 7 to 50 K and from 420 to 580 K are detected from zero-field cooled (ZFC) and field cooled (FC) dependencies of magnetization. At temperatures below 100 K, the increase of the magnetizing field leads to a sharp increase of the magnetization, which does not saturate in the magnetization field 90 kOe. The correlations between the microstructure and coercivity of the as-cast Nd–Fe alloys are discussed.