V. Moshnyaga

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

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Publications (54)219.76 Total impact

  • [Show abstract] [Hide abstract]
    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. · 2.22 Impact Factor
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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. · 4.06 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. · 7.73 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). · 3.66 Impact Factor
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    ABSTRACT: We carry out low temperature magnetotransport measurements on nanostructured La2/3Sr1/3MnO3 wires to study the interaction between spin-polarized current and magnetization in this half metallic material. We selectively position domain walls by applying external fields. The domain wall resistance is found to be positive, in contrast to conventional 3d metals. The depinning field is reduced when current pulses are injected into the wire. By comparing measurements for both current polarities, we can disentangle heating and spin transfer torque effects. The determined spin transfer torque efficiency is of the order of 4 × 10−14 Tm2/A, which is significantly higher than in permalloy.
    Applied Physics Letters 01/2014; 104(7):072410-072410-4. · 3.52 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 01/2014; · 1.88 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). · 3.77 Impact Factor
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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). · 2.21 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; · 3.77 Impact Factor
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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). · 2.21 Impact Factor
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    Physical Review B 01/2013; 87:035418. · 3.66 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). · 3.77 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). · 3.52 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 09/2011; 523(8‐9):652 - 663. · 1.51 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 (ε) and permeability (μ) and for metals at not too high frequencies the general condition for negative refraction becomes extremely simple: Re(μ)<0Re(n)<0 and may be fulfilled for such natural ferromagnetic metals as nickel, iron, or cobalt. Here we demonstrate experimentally that in pure cobalt and Fe/Co alloy the negative values of the refractive index can indeed be 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. · 2.26 Impact Factor
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    Applied Physics Letters 01/2011; 99. · 3.52 Impact Factor
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    ABSTRACT: We report the local-conductivity properties of a La0.8Ca0.2MnO3 thin film, studied by conductive atomic force microscopy. Nonvolatile and bipolar reversible switching of nanometer-sized regions was observed. A threshold voltage, Uc≈3V , and a logarithmic pulse-width dependence compatible with domain-wall creep were revealed. The results are difficult to explain in terms of an ionic drift scenario but rather indicate a switching mechanism based on orbital and accompanying structural changes. A phenomenological model of an electric field-induced structural transition is proposed.
    Physical review. B, Condensed matter 10/2010; · 3.77 Impact Factor
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    M. Schneider, V. Moshnyaga, P. Gegenwart
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    ABSTRACT: The ferromagnetic (FM) quantum phase transition in the perovskite ruthenate Sr1−xCaxRuO3 is studied by low-temperature magnetization and electrical resistivity measurements on thin films. The films were grown epitaxially on SrTiO3 substrates using metalorganic aerosol deposition and characterized by X-ray diffraction and room temperature scanning tunneling microscopy. High residual resistivity ratios of 29 and 16 for and , respectively, prove the high quality of the investigated samples. We observe a continuous suppression of the FM Curie temperature from at towards at . The analysis of the electrical resistivity between 2 and 10 K reveals T2 and T3/2 behavior at and , respectively. For undoped CaRuO3, the measurement has been extended down to 60 mK, revealing a crossover to T2 behavior around 2 K, which suggests a Fermi-liquid ground state in this system.
    physica status solidi (b) 02/2010; 247(3):577 - 579. · 1.49 Impact Factor
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    ABSTRACT: We report a memory resistance (memristor) behavior with nonlinear current-voltage characteristics and bipolar hysteretic resistance switching in the nanocolumnar manganite (LSMO) films. The switching from a high (HRS) to a low (LRS) resistance occurs at a bias field ~1 MV/cm. Applied electric field drops mostly at the insulating interfacial LSMO layer and couples to correlated polarons at the LSMO(111)/LSMO(111) vertical interfaces. The observed memristance behaviour has an electronic (polaronic) origin and is caused by an electric-field-controlled Jahn-Teller (JT) effect, followed by the orbital reconstruction and formation of a metastable orbitally disordered interfacial phase (LRS). Compared to the earlier reported ionic memristor in Ti-O films, an electronic (polaronic) nano-sized LSMO memristor shows an additional (re-entrant) LRS-HRS switching at higher fields because of the second minimum in the elastic energy of a JT system. Comment: 10 pages, 4 figures
    02/2010;
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    Physical Review B 01/2010; 82:113101. · 3.66 Impact Factor

Publication Stats

345 Citations
219.76 Total Impact Points

Institutions

  • 2014
    • Johannes Gutenberg-Universität Mainz
      • Institute of Physics
      Mayence, Rheinland-Pfalz, Germany
    • Universitätsmedizin Göttingen
      Göttingen, Lower Saxony, Germany
  • 2003–2014
    • Georg-August-Universität Göttingen
      • I. Physical Institute
      Göttingen, Lower Saxony, Germany
  • 2007
    • University of Wuerzburg
      Würzburg, Bavaria, Germany
  • 2000
    • Universität Augsburg
      • Institute of Physics
      Augsburg, Bavaria, Germany
  • 1999
    • Academy of Sciences of Moldova
      • Institute of Applied Physics
      Chişinău, Municipiul Chisinau, Moldova