V. Moshnyaga

Johannes Gutenberg-Universität Mainz, Mayence, Rheinland-Pfalz, Germany

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Publications (57)263.31 Total impact

  • Physical Review B 01/2015; 91(1). DOI:10.1103/PhysRevB.91.019901 · 3.74 Impact Factor
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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.
    Applied Physics Letters 12/2014; 105(25):251603. DOI:10.1063/1.4905055 · 3.30 Impact Factor
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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.
    Micron 11/2014; 66. DOI:10.1016/j.micron.2014.04.011 · 1.99 Impact Factor
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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.
    Journal of Physics Condensed Matter 10/2014; 26(45):456003. DOI:10.1088/0953-8984/26/45/456003 · 2.35 Impact Factor
  • 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.
    New Journal of Physics 06/2014; 16(6):063034. DOI:10.1088/1367-2630/16/6/063034 · 3.56 Impact Factor
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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.
    Physical Review Letters 05/2014; 112(20):206403. DOI:10.1103/PhysRevLett.112.206403 · 7.51 Impact Factor
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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.
    Physical Review B 01/2014; 89(2). DOI:10.1103/PhysRevB.89.024420 · 3.74 Impact Factor
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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.
    Physical review. B, Condensed matter 06/2013; 87(24). · 3.66 Impact Factor
  • 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.
    Journal of Applied Physics 03/2013; 113(17). DOI:10.1063/1.4798349 · 2.18 Impact Factor
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    ABSTRACT: We performed time-resolved nanoscale studies on the resistive switching of perovskite manganite thin films by means of conductive atomic force microscopy. Creep and recovery features have been observed in the evolution of metallic domains via pulse-train experiments and current map sequences. Local I(t) curves show 1/fα noise signatures during the switching process, a phenomenon which occurs in various physical processes consisting of discrete jumps of different sizes, such as the Barkhausen effect. Our results imply that the resistive switching falls into this universal class of effects with dynamics determined by the pinning and depinning of structural domain walls.
    Physical review. B, Condensed matter 03/2013; 87(12):121103-. DOI:10.1103/PhysRevB.87.121103 · 3.66 Impact Factor
  • S. Hühn · M. Jungbauer · M. Michelmann · F. Massel · F. Koeth · C. Ballani · V. Moshnyaga ·
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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.
    Journal of Applied Physics 02/2013; 113(17). DOI:10.1063/1.4793711 · 2.18 Impact Factor
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    S Turner · O I Lebedev · J Verbeeck · K Gehrke · V Moshnyaga · G Van Tendeloo ·
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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.
    Physical Review B 01/2013; 87(035418). DOI:10.1103/PhysRevB.87.035418 · 3.74 Impact Factor
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    Physical Review B 01/2013; 87:035418. · 3.74 Impact Factor
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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.
    JETP Letters 11/2012; 96(5). DOI:10.1134/S0021364012170079 · 1.36 Impact Factor
  • 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.
    Surface Engineering and Applied Electrochemistry 07/2012; 48(4). DOI:10.3103/S1068375512040126 · 0.29 Impact Factor
  • 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.
    Physical review. B, Condensed matter 01/2012; 85(1). DOI:10.1103/PhysRevB.85.014424 · 3.66 Impact Factor
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    ABSTRACT: We report bipolar resistive switching between the interfaces of manganite nanocolumns. La0.7Sr0.3MnO3 films were prepared on Al2O3 substrates, where the films grow in nanocolumns from the substrate to the surface. Conductive atomic force microscopy directly detects that the resistive switching is located at the boundaries of the grains. Furthermore, mesoscopic transport measurements reveal a tunnel magnetoresistance. In combination with the resistive switching, this leads to a total of four different resistive states.
    Applied Physics Letters 09/2011; 99(13). DOI:10.1063/1.3643425 · 3.30 Impact Factor
  • 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.
    Annalen der Physik 08/2011; 523(8‐9):652 - 663. DOI:10.1002/andp.201100040 · 3.05 Impact Factor
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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.
    EPL (Europhysics Letters) 07/2011; 95(3):37005. DOI:10.1209/0295-5075/95/37005 · 2.10 Impact Factor
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    Applied Physics Letters 01/2011; 99. · 3.30 Impact Factor

Publication Stats

661 Citations
263.31 Total Impact Points


  • 2014
    • Johannes Gutenberg-Universität Mainz
      • Institute of Physics
      Mayence, Rheinland-Pfalz, Germany
  • 2010-2014
    • 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