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  • 1.
    Makarova, Tatiana L
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zagaynova, Valeria
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Inan, G
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Okotrub, AV
    Chekhova, GN
    Pinakov, DV
    Bulusheva, LG
    Structural evolution and magnetic properties of underfluorinated C2F2012In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 25, no 1, p. 79-83Article in journal (Refereed)
    Abstract [en]

    A series of layered inclusion compounds based on fluorinated graphite C2F x (x≤1) was obtained by a room temperature synthesis. Inclusion compounds (intercalates) of fluorinated graphite matrix were n-hexane and dichloromethane, i.e., organic guest molecules that differ in size and symmetry. The changes in C2F x stoichiometry are shown to have a decisive effect on magnetic properties of produced complexes. The spin concentration decreases with the increase of fluorine content in fluorocarbon matrix. All samples have groups of correlated spins; at the temperatures 1.75–5 K nonlinear magnetization is observed, indicating a high-spin state. Application of the Langevin formula shows that the clusters consist of 10–20 interacting spins.

  • 2.
    Makarova, Tatiana
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zagaynova, Valeria
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Okotrub, AV
    Kurenya, AG
    Komogortsev, SV
    Bulusheva, LG
    Magnetic properties of carbon nanotubes with low content of Fe2010In: Fullerenes, nanotubes, and carbon nanostructures (Print), ISSN 1536-383X, E-ISSN 1536-4046, Vol. 18, no 4-6, p. 569-573Article in journal (Refereed)
    Abstract [en]

    Films of oriented carbon nanotubes containing different concentrations of ferrocene (0.5%, 1%, 1.5%, 2%, 2.5% and 5%) have been synthesized by CVD method and studied by means of SQUID and force microscopy. Strong dependence of magnetization process on nanotubes parameters is observed. Magnetic anisotropy of low-doped nanotubes is shown to have an easy magnetic axis perpendicular to the aligned nanotubes.

  • 3.
    Makarova, Tatiana
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Zagaynova, Valeria
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Spitsyna, Natalia G.
    Fullerene-induced magnetization training effect in single molecular magnet2010In: Physica status solidi. B, Basic research, ISSN 0370-1972, E-ISSN 1521-3951, Vol. 247, no 11, p. 3018-3021Article in journal (Refereed)
  • 4. Sasnovskaya, V
    et al.
    Kushch, L
    Yagubskii, E
    Sulimenkov, I
    Kozlovskiy, V
    Zagaynova, Valeria
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Makarova, Tatiana
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Preparation and magnetic properties of Mn-12 clusters with 4-cyanobenzenecarboxylate ligand, [Mn12O12(O2CC6H4-p-CN)(16)(H2O)(4)] and its tetraphenylphosphonium salts2012In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 324, no 18, p. 2746-2752Article in journal (Other academic)
    Abstract [en]

    The new Mn12 magnetic clusters with 4-cyanobenzenecarboxylate ligand, [Mn12O12(O2CC6H4-p-CN)16(H2O)4] (1) and its singly (2) and doubly (3) reduced analogues as their tetraphenylphosphonium salts, have been synthesized and characterized by elemental analyses, Raman, ESI-MS spectra and magnetic measurements with a SQUID magnetometer. Unlike the known Mn12 oxocarboxylate clusters, which are very soluble in CH3CN or CH2Cl2, the complex 1 is not dissolved in organic solvents providing an indication for strong intermolecular interactions which lead to strong dipole-dipole interactions between clusters and affect the magnetic behaviour. The one-electron and two-electron reduced clusters (2, 3) contain the bulk counterion and dissolve in CH3CN. They show magnetic properties characteristic for anion Mn12 single-molecule magnets.

  • 5.
    Zagaynova, Valeria
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Carbon-based magnetic nanomaterials2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Magnetism of carbon-based materials is a challenging area for both fundamental research and possible applications. We present studies of low-dimensional carbon-based magnetic systems (fullerene-diluted molecular magnets, carbon nanotubes, graphite fluoride, and nanoporous carbon) by means of SQUID magnetometer, X-ray diffraction and vibrational spectroscopy, the latter techniques used as complementary instruments to find a correlation between the magnetic behaviour and the structure of the samples.In the first part of the thesis, characteristic features of the magnetization process in aligned films of carbon nanotubes with low concentration of iron are discussed. It is shown that the magnetism of such structures is influenced by quantum effects, and the anisotropy behaviour is opposite to what is observed in heavily doped nanotubes.In the second part, Mn12-based single molecular magnets with various carboxylic ligands and their 1:1 fullerene-diluted complexes are studied. We prove that magnetic properties of such systems strongly depend on the environment, and, in principle, it is possible to design a magnet with desirable properties. One of the studied compounds demonstrated a record blocking temperature for a single molecular magnet. Both fullerene-diluted complexes demonstrated “magnetization training” effect in alternating magnetic fields and the ability to preserve magnetic moment.The third and the fourth parts of the thesis are dedicated to the analysis of various contributions to the magnetic susceptibility of metal-free carbon-based systems – intercalated compounds of graphite fluorides and nanoporous oxygen-eroded graphite. The magnetic properties of these systems are strongly dependent on structure, and can be delicately tuned by altering the π-electron system of graphite, i. e. by degree of fluorination of intercalated compounds and by introduction of boron impurity to the host matrix of nanoporous graphite.

  • 6.
    Zagaynova, Valeria
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Makarova, Tatiana L.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Spitsyna, N. G.
    Boukhvalov, D. W.
    Synthesis and magnetic properties of Mn-12-Based single molecular magnets with benzene and pentafluorobenzene carboxylate ligands2011In: Journal of Superconductivity and Novel Magnetism, ISSN 1557-1939, Vol. 24, no 1-2, p. 855-859Article in journal (Refereed)
    Abstract [en]

    We report on the synthesis and magnetic properties of Mn12-based single molecular magnets (SMMs) with benzene and pentafluorobenzene carboxylate ligands. The changes in ligand structure are shown to have a decisive effect on the magnetic properties of the complexes produced. The compound with benzene demonstrates an unusual magnetic behavior, namely, temperature dependencies of magnetization taken under the zero-field-cooled and field-cooled conditions are split below 10 K and furthermore remnant magnetization and coercive force remain nonzero in this temperature range. In contrast, the compound with pentafluorobenzene displays the customary signatures of the blocking temperature at 3 K. The effect of ligand substitution was theoretically studied within the local density approximation taking into account on-site Coloumb repulsion. Calculation results confirm that the electronic structure and the magnetic exchange interactions between different Mn atoms strongly depend on the type of ligand.

  • 7.
    Zagaynova, Valeria
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Makarova, Tatiana
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Spitsyna, N. G.
    Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, 142432 Russia.
    The magnetic memory effect in fullerene-containing single molecular magnets2010In: Bulletin of the Russian Academy of Sciences: Physics, ISSN 1062-8738, Vol. 74, no 10, p. 1426-1429Article in journal (Refereed)
    Abstract [en]

    We studied the influence of fullerenes on the properties of molecular magnets of the family of oxocarboxylate clusters of Mn12. A strong asymmetry in the hysteresis loop was observed for the first time. As opposed to the well-known effect of the displacement of a hysteresis loop along the magnetic field axis (the phenomenon of exchange bias), the observed effect of magnetic memory resides in the displacement along the vertical axis.

1 - 7 of 7
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