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Percorrer por autor "Makarov, V."

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  • Superparamagnetic properties of hemozoin
    Publication . Inyushin, M.; Kucheryavih, Yu.; Kucheryavih, L.; Rojas, L.; Khmelinskii, Igor; Makarov, V.
    We report that hemozoin nanocrystals demonstrate superparamagnetic properties, with direct measurements of the synthetic hemozoin magnetization. The results show that the magnetic permeability constant varies from mu = 4585 (at -20 degrees C) to 3843 (+20 degrees C), with the values corresponding to a superparamagnetic system. Similar results were obtained from the analysis of the diffusion separation of natural hemozoin nanocrystals in the magnetic field gradient, with mu = 6783 exceeding the value obtained in direct measurements by the factor of 1.8. This difference is interpreted in terms of structural differences between the synthetic and natural hemozoin. The ab initio analysis of the hemozoin elementary cell showed that the Fe3+ ion is in the high-spin state (S = 5/2), while the exchange interaction between Fe3+ electron-spin states was much stronger than k(B)T at room temperature. Thus, the spin dynamics of the neighboring Fe3+ ions are strongly correlated, lending support to the superparamagnetism.
    2016-05Artigo científico Acesso aberto Ver mais
  • Temperature dependence of the spin relaxation time of Fe3O4 and hemozoin superparamagnetic nanocrystals
    Publication . Khmelinskii, Igor; Makarov, V.
    We report experimental temperature and concentration dependences of the natural spin relaxation time of superparamagnetic Fe3O4 and hemozoin nanocrystals. We recorded the H-1 NMR spectrum of 0.5% benzene dissolved in CS2 in function of superparamagnetic particle concentration and temperature, interpreting the 7.261 +/- 0.002 ppm beniene line broadening. Our model for the line broadening includes natural, hyperfine magnetic dipole-dipole, and contact hyperfine contributions. The latter arises due to excharige interaction between benzene molecules and suspended nanoparticles. Estimated frequency of fluctuation in the 1 cm(3) sample volume is in the 10(7) Hz scale. Estimated natural electron spin-lattice relaxation frequencies of the superparamagnetic nanocrystals using frequency of fluctuations, and developed theoretical model applied to analysis of experimental data are in good agreement between each other. Thus the presently developed approach may be used to study fluctuations and natural spin-lattice relaxation frequencies in different media. Published by Elsevier B.V.
    2017-08Artigo científico Acesso restrito Ver mais