V. Moshnyaga

Southern Federal University, Rostov-on-Don, Rostov, Russia

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Publications (54)216.93 Total impact


  • No preview · Article · Jan 2015 · Physical Review B
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    ABSTRACT: We report an atomic layer epitaxial growth of Ruddlesden-Popper (RP) thin films of SrO(SrTiO3)n (n = ∞, 2, 3, 4) by means of metalorganic aerosol deposition (MAD). The films are grown on SrTiO3(001) substrates by means of a sequential deposition of Sr-O/Ti-O2 atomic monolayers, monitored in-situ by optical ellipsometry. X-ray diffraction and transmission electron microscopy (TEM) reveal the RP structure with n = 2–4 in accordance with the growth recipe. RP defects, observed by TEM in a good correlation with the in-situ ellipsometry, mainly result from the excess of SrO. Being maximal at the film/substrate interface, the SrO excess rapidly decreases and saturates after 5–6 repetitions of the SrO(SrTiO3)4 block at the level of 2.4%. This identifies the SrTiO3 substrate surface as a source of RP defects under oxidizing conditions within MAD. Advantages and limitations of MAD as a solution-based and vacuum-free chemical deposition route were discussed in comparison with molecular beam epitaxy.
    No preview · Article · Dec 2014 · Applied Physics Letters
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    ABSTRACT: We describe a technique using a focused ion beam instrument to fabricate high quality plan-view specimens for transmission electron microscopy studies. The technique is simple, site-specific and is capable of fabricating multiple large, >100 μm2 electron transparent windows within epitaxially-grown thin films. A film of La0.67Sr0.33MnO3 is used to demonstrate the technique and its structural and functional properties are surveyed by high resolution imaging, electron spectroscopy, atomic force microscopy and Lorentz electron microscopy. The window is demonstrated to have good thickness uniformity and a low defect density that does not impair the film's Curie temperature. The technique will enable the study of in–plane structural and functional properties of a variety of epitaxial thin film systems.
    No preview · Article · Nov 2014 · Micron
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    ABSTRACT: We investigate the effect of electric current pulse injection on domain walls in La0.7Sr0.3MnO3 (LSMO) half-ring nanostructures by high resolution x-ray magnetic microscopy at room temperature. Due to the easily accessible Curie temperature of LSMO, we can employ reasonable current densities to induce the Joule heating necessary to observe effects such as hopping of the domain walls between different pinning sites and nucleation/annihilation events. Such effects are the dominant features close to the Curie temperature, while spin torque is found to play a small role close to room temperature. We are also able to observe thermally activated domain wall transformations and we find that, for the analyzed geometries, the vortex domain wall configuration is energetically favored, in agreement with micromagnetic simulations.
    Full-text · Article · Oct 2014 · Journal of Physics Condensed Matter
  • M Jungbauer · S Hühn · J-O Krisponeit · V Moshnyaga
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    ABSTRACT: We report a colossal magnetorefractive effect (MRE) in epitaxial thin films of a classical colossal magnetoresistance (CMR) manganite, (La1???y Pry )2/3Ca1/3MnO3 (y?=?0.375 and 0.7). Close to the ferromagnetic (FM) phase transition a moderate applied magnetic field, H?~?10 kOe, results in a reduction of the optical reflectance by ~18% for the photon energy E?~?2.7 eV. The MRE spectral behavior with three pronounced maxima at E?=?1.6, 2.7 and 4.0 eV points out an inter-site nature of the involved optical transitions. The results are discussed within a phase separation scenario with coexisting FM metallic nanodomains antiferromagnetically coupled by correlated polarons. The probability of MRE optical transitions is maximal for antiparallel alignment of Mn3+/Mn4+-spins realized for the coercive field, H c?~?200?800 Oe, and is suppressed by stronger fields, which favor FM metallic behavior. As a result, both the optical reflectivity and the electrical resistance decrease, yielding a close similarity between the CMR and MRE behavior.
    No preview · Article · Jun 2014 · New Journal of Physics
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    ABSTRACT: We have prepared high-quality epitaxial thin films of CaRuO$_3$ with residual resistivity ratios up to 55. Shubnikov-de Haas oscillations in the magnetoresistance and a $T^2$ temperature dependence in the electrical resistivity only below 1.5 K, whose coefficient is substantially suppressed in large magnetic fields, establish CaRuO$_3$ as a Fermi liquid (FL) with anomalously low coherence scale. Non-Fermi liquid (NFL) $T^{3/2}$ dependence is found between 2 and 25 K. The high sample quality allows access to the intrinsic electronic properties via THz spectroscopy. For frequencies below 0.6 THz, the conductivity is Drude-like and can be modeled by FL concepts, while for higher frequencies non-Drude behavior, inconsistent with FL predictions, is found. This establishes CaRuO$_3$ as a prime example of optical NFL behavior in the THz range.
    Full-text · Article · May 2014 · Physical Review Letters
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    ABSTRACT: After the phase transition occurs in manganites La1-xCaxMnO3 (x ≥ 0.5) into a dielectric phase with charge order, right below the corresponding temperature of TCO = 240 K a series of absorption lines appear in the terahertz spectral range, only in case of commensurate x values. We show that the lines originate from acoustic phonons that become optically active by folding of the Brillouin zone. At even lower temperatures, a strongly asymmetric extra absorption band develops at frequencies around 20 cm−1 – 30 cm−1 corresponding to the position of the lowest-energy van Hove singularity in the reduced Brillouin zone. The band is assigned to the Boson Peak, i.e. to the excess of lattice vibrational states over the standard Debye contribution. The folded phonons and the boson peak do not show up for incommensurate calcium.
    Full-text · Article · Mar 2014 · Journal of Physics Conference Series
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    ABSTRACT: A commonly believed picture of colossal magnetoresistance (CMR) effect is related to a first-order phase transition and electronic phase separation with coexisting ferromagnetic metallic and antiferromagnetic insulating phases. However, the underlying mechanism, i.e., the characteristic energy scale of the interacting phases and their spatial extent, is still under debate. Here we present experimental evidence on the existence of an effective antiferromagnetic coupling between the ferromagnetic nanodomains in epitaxial thin films of a classical CMR material (La 1−y Pr y) 0.67 Ca 0.33 MnO 3 with Pr doping, y = 0.375 and 0.4. This coupling yields to peculiar low-field CMR behavior with magnetic hysteresis and slow resistance relaxation, both induced by the magnetization reversal. The coercive field obeys a square-root temperature dependence for T T C and increases anomalously close to the phase transition. We modeled the magnetic structure within the phase-separation scenario as an assembly of single-domain ferromagnetic nanoparticles, antiferromagnetically coupled (pinned) by correlated Jahn-Teller polarons. The concentration of polarons increases drastically close to phase transition as indicated by the third harmonic of the electrical conductivity as well as Raman spectroscopy.
    Full-text · Article · Jan 2014 · Physical Review B
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    ABSTRACT: In the charge-ordered phase of strongly doped manganites La1−xCaxMnO3 (x≥0.5) absorption lines appear in the terahertz spectral range for commensurate x values right below the charge-ordering temperature. They are connected to acoustic phonons that become optically active by folding of the Brillouin zone. At lower temperatures a strongly asymmetric extra absorption band develops at frequencies corresponding to the position of the lowest-energy van Hove singularity in the reduced Brillouin zone. The band is assigned to the boson peak, i.e., to the excess of lattice vibrational states over the standard Debye contribution. The folded phonons and the boson peak do not show up for incommensurate calcium contents when no distinct Brillouin zone folding exists.
    Full-text · Article · Jun 2013 · Physical review. B, Condensed matter
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    ABSTRACT: This chapter shows that FeSb2Se4 exhibits ferromagnetism and semiconductity above 300K and undergoes structural-distortion-driven cooperative magnetic and semiconductor-to-insulator (SI) transitions upon cooling below 130K. It examines the systematically different geometries of two dimensional (2D) nickel nanostrips using spin density functional theory. The chapter also shows a fundamentally different phenomena in the ferromagnetic manganite Sm0.6Sr0.4MnO3. In-plane magnetotransport properties of a EuFe2As2 single crystal are investigated by angular dependent magnetoresistance measurements. In colossal magnetoresistance (CMR) manganites strong electronic correlations may be influenced and/or induced by electronphonon interaction. The narrow band gap semiconductor Sb2Te3 belongs to the class of phase change materials, which may be employed for future electrical and optical data storage. The chapter focuses on electrical properties of Bi0.95Nd0.05FeO3 thin film (BNFO05) deposited on Pt/TiO2/SiO2/Si (100) substrates by the soft chemical method. band theory; colossal magnetoresistance; ferromagnetic materials; phase change materials
    No preview · Article · Apr 2013
  • M. Jungbauer · S. Hühn · M. Michelmann · E. Goering · V. Moshnyaga
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    ABSTRACT: Exchange bias (EB) has been observed for all-manganite La0.7Sr0.3MnO3/SrMnO3/La0.7Sr0.3MnO3 trilayers with ferromagnetic La0.7Sr0.3MnO3 and G-type antiferromagnetic SrMnO3 (SMO) layers, grown on (001) SrTiO3 substrates by metalorganic aerosol deposition. The field shift of the magnetic hysteresis loop HE and the coercivity HC decay exponentially with temperature. HE exhibits a global maximum as a function of SMO interlayer thickness at tSMO ≈ 4.5 nm. We argue that EB behaviour can be explained by the interplay of a spinglass state at the interface and theoretically proposed mechanism based on the Dzyaloshinskii-Moriya interaction.
    No preview · Article · Mar 2013 · Journal of Applied Physics
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    ABSTRACT: Colossal magnetoresistance (CMR) and nm-scale electronic inhomogeneity close to the first order phase transition in perovskite manganites, e.g., (La1−yPry)0.67Ca0.33MnO3 still remain a puzzling phenomenon. We experimentally model a metal-insulator phase coexistence by growing a short period (LCMOn/PCMOn)m superlattices (SLs) with the same thickness for both components. CMR effect was studied as a function of the individual layer thickness n = 2–8 and then compared with chemically homogeneous (La1−yPry)0.67Ca0.33MnO3 LPCMO films. We show that SLs can be superimposed in the phase diagram of LPCMO. The results also point out the importance of the nm-scale electronic rather than chemical separation for realization of the CMR effect as well as limits the lowest boundary for the thickness of an individual manganite material to n ∼ 4u.c.
    No preview · Article · Feb 2013 · Journal of Applied Physics
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    ABSTRACT: La 2/3 Ca 1/3 MnO 3) n /(BaTiO 3) m (LCMO n /BTO m) superlattices on MgO and SrTiO 3 substrates with different layer thicknesses (n = 10, 38, 40 and m = 5, 18, 20) have been grown by metal organic aerosol deposition (MAD) and have been fully characterized down to the atomic scale to study the interface characteristics. Scanning transmission electron microscopy combined with spatially resolved electron energy-loss spectroscopy provides clear evidence for the existence of atomically sharp interfaces in MAD grown films, which exhibit epitaxial growth conditions, a uniform normal strain, and a fully oxidized state. Below a critical layer thickness the LCMO structure is found to change from the bulk Pnma symmetry to a pseudocubic R ¯ 3c symmetry. An atomically flat interface reconstruction consisting of a single Ca-rich atomic layer is observed on the compressively strained BTO on LCMO interface, which is thought to partially neutralize the total charge from the alternating polar atomic layers in LCMO as well as relieving strain at the interface. No interface reconstruction is observed at the tensile strained LCMO on BTO interface.
    Full-text · Article · Jan 2013 · Physical Review B
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    Full-text · Article · Jan 2013 · Physical Review B
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    M. S. Ivanov · E. D. Mishina · V. Moshnyaga · M. Fiebig
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    ABSTRACT: The electronic structure of doped orthorhombic (La0.6Pr0.4)0.7Ca0.3MnO3 manganite is studied using the second optical harmonic generation method. The analysis of the frequency and polarization dependence of the intensity related to the second harmonic demonstrates that the applied magnetic field stimulates a transition of spin-polarized electrons from the d orbitals of Mn ions to the p orbitals of O2 ligands. The manifestation of such transition in the orthorhombic RMnO3 manganite with the distorted crystal lattice is attributed to the dipole-forbidden electronic transitions arising in the applied magnetic field. The mechanism of magnetooptical activity induced by the charge transfer between Mn and O ions is discussed.
    Full-text · Article · Nov 2012 · JETP Letters
  • A. N. Nateprov · V. Ch. Kravtsov · V. Moshnyaga · S. Schorr
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    ABSTRACT: The crystal structure of YbCuZnSb2 has been determined for the first time by single-crystal X-ray diffraction analysis. It is shown that YbCuZnSb2 has a CaAl2Si2-type structure, space group is P-3m1, with the following unit cell parameters: a = 4.4394(1) and c = 7.4139(3) Å. Magnetic susceptibility measurements performed in the temperature range from 2 to 300 K show that ytterbium ions are found in a nonmagnetic 4f 14 ground state (Yb2+). YbCuZnSb2 exhibits p-type conductivity. The temperature dependence of the resistivity has a metallic character. The variations in the Cu/Zn ratio in the synthesized material occur without any disturbance of the structural type. This fact may confirm the existence of a solid solution between the YbZn2Sb2 and YbCuZnSb2 compounds.
    No preview · Article · Jul 2012 · Surface Engineering and Applied Electrochemistry
  • M. Michelmann · V. Moshnyaga · K. Samwer
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    ABSTRACT: (La0.6Pr0.4)0.7Ca0.3MnO3 was characterized by means of ultrasound velocity and attenuation to study the temperature and magnetic field dependence of the elastic constants and to gain an insight into the metamagnetic transition. The metal-insulator and ferromagnetic-paramagnetic transitions are reflected in the behavior of the elastic constants due to strong electron-phonon and spin-phonon interactions. A hysteresis in elastic behavior and metamagnetism hints toward first-order nature of the phase transition. A softening of bulk modulus at the ferromagnetic transition for magnetic fields μ0H>2 T was attributed to a coupling between the lattice and spin fluctuations. This softening peaks at a certain temperature T*≈215 K and field μ0H*≈4 T, which could be an indication of a critical end point of the ferromagnetic transition.
    No preview · Article · Jan 2012 · Physical review. B, Condensed matter
  • V. Moshnyaga · K. Samwer
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    ABSTRACT: Interrelations between global and local structure and magnetism and transport in three-dimensional perovskite manganites is reviewed and compared with recent studies on thin films and superlattices. The concept of correlated Jahn-Teller (JT) polarons is discussed within the phase separation scenario; their role in the local and global structural modifications of manganites is demonstrated. Polaron correlations, affected by external control parameters (temperature, electric and magnetic fields, doping, light, strain) may be very efficient to modify the ground state of manganites. Examples of electronic control of the structure by means of interface modifications, electric field and mechanical strain are highlighted.
    No preview · Article · Aug 2011 · Annalen der Physik
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    ABSTRACT: It is generally believed that Veselago's criterion for negative refraction cannot be fulfilled in natural materials. However, considering imaginary parts of the permittivity ({\epsilon}) and permeability ({\mu}) and for metals at not too high frequencies the general condition for negative refraction becomes extremely simple: Re({\mu}) < 0 --> Re(n) < 0. Here we demonstrate experimentally that in such natural metals as pure Co and FeCo alloy the negative values of the refractive index are achieved close to the frequency of the ferromagnetic resonance. Large values of the negative refraction can be obtained at room temperature and they can easily be tuned in moderate magnetic fields.
    Full-text · Article · Jul 2011 · EPL (Europhysics Letters)
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    Preview · Article · Jan 2011 · Applied Physics Letters

Publication Stats

616 Citations
216.93 Total Impact Points

Institutions

  • 2014
    • Southern Federal University
      • Faculty of Physics
      Rostov-on-Don, Rostov, Russia
    • Johannes Gutenberg-Universität Mainz
      • Institute of Physics
      Mayence, Rheinland-Pfalz, Germany
  • 2007-2014
    • Universitätsmedizin Göttingen
      Göttingen, Lower Saxony, Germany
  • 2002-2014
    • Georg-August-Universität Göttingen
      • • I. Physical Institute
      • • IV. Physical Institute
      Göttingen, Lower Saxony, Germany
    • University of Antwerp
      Antwerpen, Flemish, Belgium
  • 2000
    • Universität Augsburg
      • Institute of Physics
      Augsberg, Bavaria, Germany
  • 1999
    • Academy of Sciences of Moldova
      • Institute of Applied Physics
      Chişinău, Municipiul Chisinau, Moldova