Dimerization and low-dimensional magnetism in nanocrystalline TiO2 semiconductors doped by Fe and Co

The report is devoted to an analysis of the structural and magnetic state of the nanocrystalline diluted magnetic semiconductors based on TiO2 doped with Fe and Co atoms. Structural and magnetic characterization of samples was carried out using X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR) spectroscopy, SQUID magnetometry, and the density functional theory (DFT) calculations. Analysis of the experimental data suggests the presence of non-interacting paramagnetic Fe3+ and Co2+ ions in the high-spin state and negative exchange interactions between them. The important conclusions is that the distribution of dopants in the TiO2 matrix, even at low concentrations of 3d-metal dopant (less than one percent), is not random, but the 3d ions localization and dimerization is observed both on the surface and in the nanoparticles core. Thus, in the paper the quantum mechanical model for describing the magnetic properties of TiO2:(Fe, Co) was suggested. The model operates only with two parameters: paramagnetic contribution of non-interacting 3d-ions and dimers having different exchange interactions between 3d magnetic carriers. © Published under licence by IOP Publishing Ltd

Application of Nanoparticles with the Structure of the Metal Nucleus - Carbon Enclosure in Biology and Medicine

The study was carried out with the financial support of the Russian Foundation for Basic Research in the framework of the research project No. 18-33-00785

Unconventional magnetism of non-uniform distribution of Co in TiO2 nanoparticles

High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), magnetic methods, and density-functional theory (DFT) calculations were applied for the investigations of Co-doped anatase TiO2 nanoparticles (∼20 nm). It was found that high-spin Co2+ ions prefer to occupy the interstitial positions in the TiO2 lattice which are the most energetically favourable in compare to the substitutional those. A quantum mechanical model which operates mainly on two types of Co2+ – Co2+ dimers with different negative exchange interactions and the non-interacting paramagnetic Co2+ ions provides a satisfactorily description of magnetic properties for the TiO2:Co system. © 2020 Elsevier B.V.Russian Foundation for Basic Research. Ministry of Science and Higher Education of the Russian Federatio

Plastic Deformation of Polycrystalline Iridium at Room Temperature

Defect structure and its relationship with deformation behaviour at room temperature of iridium, the sole refractory face centred cubic (f.c.c.) metal, are discussed. Small angle boundaries and pile-ups of curvilinear dislocation segments are the main features of dislocation structure in polycrystalline iridium at room temperature, while homogeneously distributed rectilinear dislocation segments were the main element of defect structure of iridium single crystals at the same conditions. Small angle boundaries and pile-ups of curvilinear dislocation segments are formed in iridium single crystals under mechanical treatment at elevated temperatures (> 800°C) only. The evolution of defect structure in polycrystalline iridium and other f.c.c. metals under room temperature deformation occurs by the same process: accumulation of dislocations in the matrix leads to the appearance of both new sub-grains and new grains up to the fine grain (nanocrystalline) structure. Neither single straight dislocations nor their pile-ups are observed in iridium at room temperature if small angle boundaries have been formed. This feature may be considered as the reason why polycrystalline iridium demonstrates advanced necking (high localised plasticity) and small total elongation.The authors would like to thank Professor David Lupton (W. C. Heraeus GmbH, Hanau, Germany) and Professor Easo George (The University of Tennessee, Knoxville, Tennessee, U.S.A.) for helpful discussions. This research was partially supported by the JSC Ekaterinburg NonFerrous Metals Processing Plant, the Ministry of Education and Science of the Russian Federation (Grant No. 2.2.2.2/5579) and the U.S. Civilian Research and Development Foundation (CRDF) (Grant No. RUXO-005-EK-06/BG7305)

Atomic, electronic and magnetic structure of graphene/iron and nickel interfaces: theory and experiment

First-principles calculations of the effect of carbon coverage on the atomic, electronic and magnetic structure of nickel and iron substrates demonstrate insignificant changes in the interatomic distances and magnetic moments on the atoms of the metallic substrates. The coverage of the iron surface by mono- and few-layer graphene induces significant changes in the orbital occupancies and exchange interactions between the layers in contrast to the case of a nickel substrate for which changes in the orbital ordering and exchange interactions are much smaller. Experimental measurements demonstrate the presence of ferromagnetic fcc-iron in Fe@C nanoparticles and the superparamagnetic behavior of Ni@C nanoparticles.Comment: 19 pages, 7 figures, accepted to RSC Advance