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Sample records for quasi-two-dimensional antiferromagnet er5ir4si10

  1. Antiferromagnetic fluctuations in a quasi-two-dimensional organic superconductor detected by Raman spectroscopy.

    Energy Technology Data Exchange (ETDEWEB)

    Drichko, Natalia; Hackl, Rudi; Schlueter, John A.

    2015-10-15

    Using Raman scattering, the quasi-two-dimensional organic superconductor kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Br (T-c = 11.8 K) and the related antiferromagnet kappa-(BEDT-TTF)(2)Cu[N(CN)(2)]Cl are studied. Raman scattering provides unique spectroscopic information about magnetic degrees of freedom that has been otherwise unavailable on such organic conductors. Below T = 200 K a broad band at about 500 cm(-1) develops in both compounds. We identify this band with two-magnon excitation. The position and the temperature dependence of the spectral weight are similar in the antiferromagnet and in the metallic Fermi liquid. We conclude that antiferromagnetic correlations are similarly present in the magnetic insulator and the Fermi-liquid state of the superconductor.

  2. Semi-phenomenological analysis of neutron scattering results for quasi-two dimensional quantum anti-ferromagnet

    Science.gov (United States)

    Sarkar, Subhajit; Chaudhury, Ranjan; Paul, Samir K.

    2017-01-01

    The available results from the inelastic neutron scattering experiment performed on the quasi-two dimensional spin 1/2 anti-ferromagnetic material La2CuO4 have been analysed theoretically. The formalism of ours is based on a semi-classical like treatment involving a model of an ideal gas of mobile vortices and anti-vortices built on the background of the Néel state, using the bipartite classical spin configuration corresponding to an XY-anisotropic Heisenberg anti-ferromagnet on a square lattice. The results for the integrated intensities for our spin 1/2 model corresponding to different temperatures, show occurrence of vigorous unphysical oscillations, when convoluted with a realistic spectral window function. These results indicate failure of the conventional semi-classical theoretical model of ideal vortex/anti-vortex gas arising in the Berezinskii-Kosterlitz-Thouless theory for the low spin magnetic systems. A full fledged quantum mechanical formalism and calculations seem crucial for the understanding of topological excitations in such low spin systems. Furthermore, a severe disagreement is found to occur at finite values of energy transfer between the integrated intensities obtained theoretically from the conventional formalism and those obtained experimentally. This further suggests strongly that the full quantum treatment should also incorporate the interaction between the fragile-magnons and the topological excitations. This is quite plausible in view of the recent work establishing such a process in XXZ quantum ferromagnet on 2D lattice. The high spin XXZ quasi-two dimensional antiferromagnet like MnPS3 however follows the conventional theory quite well.

  3. Quantum Phase Transition in Quasi-two-dimensional Heisenberg Antiferromagnet with Single-Ion Anisotropy

    Institute of Scientific and Technical Information of China (English)

    JI An-Chun; TIAN Guang-Shan

    2007-01-01

    In the present paper, we investigate the quantum phase transition in a spatially anisotropic antiferromagnetic Heisenberg model of S = 1 with single-ion energy anisotropy. By using the Schwinger boson representation, we calculate the Gaussian correction to the critical value Jc⊥ caused by quantum spin fluctuations. We find that, for the positive single-ion energy, a nonzero value of Jc⊥ is always needed to stabilize the antiferromagnetic long-range order in this model. It resolves a difference among literature and shows clearly that the effect of quantum fluctuations may qualitatively change a result obtained by the mean-field theories on lower-dimensional systems.

  4. d-wave superconductivity, antiferromagnetism and spin liquid in quasi-two-dimensional organic superconductors

    Directory of Open Access Journals (Sweden)

    P. Sahebsara

    2006-09-01

    Full Text Available   The self-energy-functional approach is a powerful many-body tool to investigate different broken symmetry phases of strongly correlated electron systems. We use the variational cluster perturbation theory (also called the variational cluster approximation to investigate the interplay between the antiferromagnetism and d-wave superconductivity of κ-(ET2 X conductors. These compounds are described by the so-called dimer Hubbard model, with various values of the on-site repulsion U and diagonal hopping amplitude t. At strong coupling, our zero-temperature calculations show a transition from Néel antiferromagnetism to a spin-liquid phase with no long range order, at around t ~ 0.9. At lower values of U, we find d-wave superconductivity. Taking into account the point group symmetries of the lattice, we find a transition between dx2-y2 and dxy pairing symmetries, the latter happening for smaller values of U.

  5. Spin transport of the frustrated quasi-two-dimensional XY-like antiferromagnet

    Science.gov (United States)

    Lima, L. S.

    2017-01-01

    We use the Self Consistent Harmonic Approximation together with the Kubo formalism of the Linear Response Theory to study the spin transport in the two-dimensional frustrated Heisenberg antiferromagnet in a square lattice with easy-plane ion single anisotropy. The regular part of the spin conductivity σreg(ω) is determined for several values of the critical ion single parameter Dc, that separates the low D region from the large D quantum paramagnetic phase. We have obtained an abrupt change in the spin conductivity in the discontinuity points of the graphic Dc vs. η, where the system presents a quantum phase transition.

  6. Quantum critical response function in quasi-two-dimensional itinerant antiferromagnets

    Science.gov (United States)

    Varma, C. M.; Zhu, Lijun; Schröder, Almut

    2015-10-01

    We reexamine the experimental results for the magnetic response function χ''(q ,E ,T ) for q around the antiferromagnetic vectors Q , in the quantum-critical region, obtained by inelastic neutron scattering, on an Fe-based superconductor and on a heavy-fermion compound. The motivation is to compare the results with a recent theory, which shows that the fluctuations in a generic antiferromagnetic model for itinerant fermions map to those in the universality class of the dissipative quantum-XY model. The quantum-critical fluctuations in this model, in a range of parameters, are given by the correlations of spatial and temporal topological defects. The theory predicts a χ''(q ,E ,T ) (i) which is a separable function of (q -Q ) and of (E ,T ) , (ii) at criticality, the energy-dependent part is ∝tanh(E /2 T ) below a cutoff energy, (iii) the correlation time departs from its infinite value at criticality on the disordered side by an essential singularity, and (iv) the correlation length depends logarithmically on the correlation time, so that the dynamical critical exponent z is ∞ . The limited existing experimental results are found to be consistent with the first two unusual predictions from which the linear dependence of the resistivity on T and the T lnT dependence of the entropy also follow. More experiments are suggested, especially to test the theory of variations on the correlation time and length on the departure from criticality.

  7. O2- -to-F- substitution on the quasi-two-dimensional quantum antiferromagnet (CuCl)LaNb2O7

    Science.gov (United States)

    Tassel, C.; Kobayashi, Y.; Mitsuoka, S.; Takeiri, F.; Ajiro, Y.; Kageyama, H.

    2011-09-01

    We present the preparation of the electron-doped quasi-two dimensional quantum antiferromagnet (CuCl)LaNb2O7 by two step-wise topochemical reactions. The first step involves a reductive fluorination of the insulating layered perovskite RbLaNb2O7 using polytetrafluoroethylene that allows electric conduction in the perovskite blocks. The product RbLaNb2O6F was then ion-exchanged with copper dichloride to yield (CuCl)LaNb2O6F. The synchrotron x-ray diffraction study indicates that the structure of the final compound is different from that of the pure (CuCl)LaNb2O7.

  8. The magnetic properties of a quasi-two-dimensional spin 1 easy axis Heisenberg antiferromagnet with competing interactions

    Energy Technology Data Exchange (ETDEWEB)

    Sousa, Griffith Mendonça A., E-mail: griffith_mas@hotmail.com; Pires, A.S.T.

    2014-03-15

    The Neel and collinear ordered phases of the two-dimensional S=1 antiferromagnet with next and next near neighbor exchange interactions and easy axis single ion anisotropy, on the square lattice, are studied at low temperature using a Modified Spin Wave Theory. We calculate the low-temperature quantities as a function of the temperature, frustration and anisotropy. We calculate also the phase diagram at T=0. We found a disordered phase separating the Neel and collinear phases. - Highlights: • The phase diagrams in zero temperature. • The critical temperature was studied as a function of frustration and D. • The sublattice magnetizations and the gap were studied.

  9. Magnetic phases of the quasi-two-dimensional antiferromagnet CuCrO2 on a triangular lattice

    Science.gov (United States)

    Sakhratov, Yu. A.; Svistov, L. E.; Kuhns, P. L.; Zhou, H. D.; Reyes, A. P.

    2016-09-01

    We have carried out Cu,6563 NMR spectra measurements in a magnetic field up to about 45 T on a single crystal of a multiferroic triangular antiferromagnet CuCrO2. The measurements were performed for magnetic fields aligned along the crystal c axis. Field and temperature evolution of the spectral shape demonstrates a number of phase transitions. It was found that the 3D magnetic ordering takes place in the low field range (H ≲15 T). At higher fields magnetic structures form within individual triangular planes whereas the spin directions of the magnetic ions from neighboring planes are not correlated. It is established that the 2D-3D transition is hysteretic in field and temperature. Line-shape analysis reveals several possible magnetic structures existing within individual planes for different phases of CuCrO2. Within certain regions on the magnetic H -T phase diagram of CuCrO2 a 3D magnetic ordering with tensor order parameter is expected.

  10. Anisotropic electronic and magnetic properties of the quasi-two-dimensional heavy-fermion antiferromagnet CeRhIn{sub 5}

    Energy Technology Data Exchange (ETDEWEB)

    Cornelius, A. L.; Arko, A. J.; Sarrao, J. L.; Hundley, M. F.; Fisk, Z.

    2000-12-01

    We have used high pulsed magnetic fields to 50 T to observe de Haas--van Alphen oscillations in the tetragonal antiferromagnet CeRhIn{sub 5}, which has an enhanced value of the electronic specific heat coefficient {gamma}{approx}>420 mJ/molK{sup 2}. For Tquasi-two-dimensional crystal structure.

  11. Quasi-two-dimensional Fermi surfaces in the flat antiferromagnetic Brillouin zone of NpRhGa{sub 5} studied by dHvA experiments and energy band calculations

    Energy Technology Data Exchange (ETDEWEB)

    Aoki, Dai [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Yamagami, Hiroshi [Department of Physics, Faculty of Science, Kyoto Sangyo University, Kyoto 603-8555 (Japan); Homma, Yoshiya [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Shiokawa, Yoshinobu [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Yamamoto, Etsuji [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Nakamura, Akio [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Haga, Yoshinori [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan); Settai, Rikio [Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan); Onuki, Yoshichika [Advanced Science Research Center, Japan Atomic Energy Research Institute, Tokai, Ibaraki 319-1195 (Japan)

    2005-05-04

    We succeeded in growing a high-quality single crystal of NpRhGa{sub 5} by the Ga-flux method and observed the de Haas-van Alphen oscillation in the antiferromagnetic state. Four kinds of nearly cylindrical Fermi surfaces, which correspond to main Fermi surfaces, were clearly detected. These quasi-two-dimensional Fermi surfaces are formed in the flat antiferromagnetic Brillouin zone and are well explained on the basis of spin- and orbital-polarized LAPW energy band calculations. The cyclotron masses are moderately enhanced, ranging from 8.1 to 11.7 m{sub 0}, which are approximately four times larger than the corresponding band masses. This is the first case where the 5f-itinerant band model is applicable to a neptunium magnetic compound. (letter to the editor)

  12. Zigzag antiferromagnetic ground state with anisotropic correlation lengths in the quasi-two-dimensional honeycomb lattice compound N a2C o2Te O6

    Science.gov (United States)

    Bera, A. K.; Yusuf, S. M.; Kumar, Amit; Ritter, C.

    2017-03-01

    The crystal structure, magnetic ground state, and the temperature-dependent microscopic spin-spin correlations of the frustrated honeycomb lattice antiferromagnet N a2C o2Te O6 have been investigated by powder neutron diffraction. A long-range antiferromagnetic (AFM) ordering has been found below TN˜24.8 K . The magnetic ground state, determined to be zigzag antiferromagnetic and characterized by a propagation vector k =(1 /2 0 0 ) , occurs due to the competing exchange interactions up to third-nearest neighbors within the honeycomb lattice. The exceptional existence of a limited magnetic correlation length along the c axis (perpendicular to the honeycomb layers in the a b planes) has been found even at 1.8 K, well below the TN˜24.8 K . The observed limited correlation along the c axis is explained by the disorder distribution of the Na ions within the intermediate layers between honeycomb planes. The reduced ordered moments mCo (1 )=2.77 (3 ) μB/C o2 + and mCo (2 )=2.45 (2 ) μB/C o2 + at 1.8 K reflect the persistence of spin fluctuations in the ordered state. Above TN˜24.8 K , the presence of short-range magnetic correlations, manifested by broad diffuse magnetic peaks in the diffraction patterns, has been found. Reverse Monte Carlo analysis of the experimental diffuse magnetic scattering data reveals that the spin correlations are mainly confined within the two-dimensional honeycomb layers (a b plane) with a correlation length of ˜12 Å at 25 K. The nature of the spin arrangements is found to be similar in both the short-range and long-range ordered magnetic states. This implies that the short-range correlation grows with decreasing temperature and leads to the zigzag AFM ordering at T ≤TN . The present study provides a comprehensive picture of the magnetic correlations over the temperature range above and below the TN and their relation to the crystal structure. The role of intermediate soft Na layers on the magnetic coupling between honeycomb planes is

  13. Quasi-Two-Dimensional Magnetism in Co-Based Shandites

    Science.gov (United States)

    Kassem, Mohamed A.; Tabata, Yoshikazu; Waki, Takeshi; Nakamura, Hiroyuki

    2016-06-01

    We report quasi-two-dimensional (Q2D) itinerant electron magnetism in the layered Co-based shandites. Comprehensive magnetization measurements were performed using single crystals of Co3Sn2-xInxS2 (0 ≤ x ≤ 2) and Co3-yFeySn2S2 (0 ≤ y ≤ 0.5). The magnetic parameters of both systems; the Curie temperature TC, effective moment peff and spontaneous moment ps; exhibit almost identical variations against the In- and Fe-concentrations, indicating significance of the electron count on the magnetism in the Co-based shandite. The ferromagnetic-nonmagnetic quantum phase transition is found around xc ˜ 0.8. Analysis based on the extended Q2D spin fluctuation theory clearly reveals the highly Q2D itinerant electron character of the ferromagnetism in the Co-based shandites.

  14. Quasi-two-dimensional Dirac fermions and quantum magnetoresistance in LaAgBi$_2$

    OpenAIRE

    Wang, Kefeng; Graf, D.; Petrovic, C.

    2016-01-01

    We report quasi-two-dimensional Dirac fermions and quantum magnetoresistance in LaAgBi$_2$. The band structure shows several narrow bands with nearly linear energy dispersion and Dirac-cone-like points at the Fermi level. The quantum oscillation experiments revealed one quasi-two-dimensional Fermi pocket and another complex pocket with small cyclotron resonant mass. The in-plane transverse magnetoresistance exhibits a crossover at a critical field $B^*$ from semiclassical weak-field $B^2$ dep...

  15. Three-dimensional magnetic interactions in quasi-two-dimensional PdAs2O6

    Science.gov (United States)

    Zhao, Z. Y.; Wu, Y.; Cao, H. B.; Zhou, H. D.; Yan, J.-Q.

    2017-06-01

    Millimeter-sized PdAs2O6 single crystals are grown using the vapor transport technique. The magnetic order at {{T}\\text{N}}=140 K is studied by measuring magnetic properties, specific heat, and neutron single crystal diffraction. The anisotropic magnetic susceptibility and a metamagnetic transition observed in magnetic fields above 20 kOe suggest that the magnetic moment lies in the ab plane, consistent with the magnetic structure determined by neutron single crystal diffraction. Below 140 K, Pd2+ ions order ferromagnetically in the ab plane but antiferromagnetically along the crystallographic c axis. The ordered moment is refined to be 2.09(2) {μ\\text{B}} /Pd2+ using the fitted magnetic form factor of Pd2+ . A weak λ-type anomaly around T N was observed in specific heat and the magnetic entropy change across T N is 1.72 J mol-1 K.This small entropy change and the temperature dependence of the magnetic susceptibility support the presence of short range correlations in a wide temperature range {{T}\\text{N}} 250 K. The comparison with SrRu2O6 suggests that the magnetic interactions in PdAs2O6 are dominated by Pd-(O-\\text{As}\\text{As} -O)-Pd super-superexchange and three dimensional despite the quasi-two-dimensional arrangement of magnetic ions. The comparison with NiAs2O6 suggests that increasing covalency of isostructural compounds is an effective approach to design and to discover new materials with higher magnetic order temperatures in the localized regime.

  16. Collective modes of a quasi-two-dimensional Bose condensate in large gas parameter regime

    Indian Academy of Sciences (India)

    S R Mishra; S P Ram; Arup Banerjee

    2007-06-01

    We have theoretically studied the collective modes of a quasi-two-dimensional (Q2D) Bose condensate in the large gas parameter regime by using a formalism which treats the interaction energy beyond the mean-field approximation. The results show that incorporation of this higher order term leads to significant modifications in the mode frequencies.

  17. Quasi-particle properties in a quasi-two-dimensional electron liquid

    Indian Academy of Sciences (India)

    R Asgari; B Tanatar

    2008-02-01

    We consider the quasi-particle properties such as the effective mass and spin susceptibility of quasi-two-dimensional electron systems. The finite quantum well width effects are incorporated into the local-field factors that describe the charge and spin correlations. We employ the Fermi-hypernetted chain formalism in conjunction with fluctuation-dissipation theorem to obtain the local-field factors. Our results are in good agreement with recent experiments.

  18. Three-body recombination in a quasi-two-dimensional quantum gas

    Science.gov (United States)

    Huang, Bo; Zenesini, Alessandro; Grimm, Rudolf

    2016-05-01

    Quantum three-body recombination in three-dimensional systems is influenced by a series of weakly bound trimers known as Efimov states, which are induced by short-range interactions and exhibit a discrete scaling symmetry. On the other hand, two-dimensional systems with contact interactions are characterized by continuous scale invariance and support no Efimov physics. This raises questions about the behaviour of three-body recombination in the transition from three to two dimensions. We use ultracold caesium atoms trapped in anisotropic potentials formed by a pair of counter-propagating laser beams to experimentally investigate three-body recombination in quasi-two-dimensional systems with tunable confinement and tunable interactions. In our recent experiments, we observed a smooth transition of the three-body recombination rate coefficient from a three-dimensional to a deeply quasi-two-dimensional system. A comparison between the results obtained near two Feshbach resonances indicates a universal behaviour of three-body recombination in the quasi-two-dimensional regime. Austrian Science Fund FWF within project P23106.

  19. Negative static permittivity and violation of Kramers-Kronig relations in quasi-two-dimensional crystals

    Science.gov (United States)

    Nazarov, V. U.

    2015-10-01

    We investigate the wave vector and frequency-dependent screening of the electric field in atomically thin (quasi-two-dimensional) crystals. For graphene and hexagonal boron nitride we find that, above a critical wave vector qc, the static permittivity ɛ (q >qc,ω =0 ) becomes negative and the Kramers-Kronig relations do not hold for ɛ (q >qc,ω ) . Thus, in quasi-two-dimensional crystals, we reveal the physical confirmation of a proposition put forward decades ago [D. A. Kirzhnits, Sov. Phys. Usp. 19, 530 (1976), 10.1070/PU1976v019n06ABEH005268], allowing for the breakdown of Kramers-Kronig relations and for negative static permittivity. In the vicinity of the critical wave vector, we find a giant growth of the permittivity. Our results, obtained in the ab initio calculations using both the random-phase approximation and the adiabatic time-dependent local-density approximation, and further confirmed with a simple slab model, allow us to argue that the above properties, being exceptional in the three-dimensional case, are common to quasi-two-dimensional systems.

  20. Quasi-two-dimensional complex plasma containing spherical particles and their binary agglomerates

    CERN Document Server

    Chaudhuri, M; Nosenko, V; Thomas, H M

    2015-01-01

    A new type of quasi-two-dimensional complex plasma system was observed which consisted of monodisperse microspheres and their binary agglomerations (dimers). The particles and their dimers levitated in a plasma sheath at slightly different heights and formed two distinct sublayers. The sys- tem did not crystallize and may be characterized as disordered solid. The dimers were identified based on their characteristic appearance in defocused images, i.e., rotating interference fringe pat- terns. The in-plane and inter-plane particle separations exhibit nonmonotonic dependence on the discharge pressure which agrees well with theoretical predictions.

  1. Block copolymer micelle coronas as quasi-two-dimensional dilute or semidilute polymer solutions

    DEFF Research Database (Denmark)

    Svaneborg, C.; Pedersen, J.S.

    2001-01-01

    Chain-chain interactions in a corona of polymers tethered to a spherical core under good solvent conditions are studied using Monte Carlo simulations. The total scattering function of the corona as well as different partial contributions are sampled. By combining the different contributions...... in a self-consistent approach, it is demonstrated that the corona can be regarded as a quasi-two-dimensional polymer solution, with a concentration dependence analogous to that of an ordinary polymer solution. Scattering due to the corona profile and density fluctuation correlations are separated...

  2. Characterizing Mixing in a Quasi-Two-Dimensional Flow using Persistent Homology

    Science.gov (United States)

    Tithof, Jeffrey; Kelley, Douglas

    2016-11-01

    Fluid mixing is a tremendously important phenomenon present in numerous physical systems, both natural and human-made. Describing, understanding, and predicting the mixing behavior of fluid flows poses an immense challenge. In this work, we explore the utility of topological data analysis in quantifying fluid mixing. We analyze Eulerian and Lagrangian quantities obtained from a quasi-two-dimensional flow realized by driving a thin layer of fluid with electromagnetic forces. Our analysis employs persistent homology, which offers a unique framework for quantifying topological features associated with connectivity in the fluid flow. Preliminary results suggest that this topological approach offers new physical insight, complementing existing methods for quantifying fluid mixing.

  3. Slow dynamics in a quasi-two-dimensional binary complex plasma

    CERN Document Server

    Du, Cheng-Ran; Thomas, Hubertus M; Morfill, Gregor E; Ivlev, Alexei V

    2016-01-01

    Slow dynamics in an amorphous quasi-two-dimensional complex plasma, comprised of microparticles of two different sizes, was studied experimentally. The motion of individual particles was observed using video microscopy, and the self part of the intermediate scattering function as well as the mean-squared particle displacement was calculated. The long-time structural relaxation reveals the characteristic behavior near the glass transition. Our results suggest that binary complex plasmas can be an excellent model system to study slow dynamics in classical supercooled fluids.

  4. Hall Conductivity in a Quasi-Two-Dimensional Disordered Electron System

    Institute of Scientific and Technical Information of China (English)

    YANG Yong-Hong; WANG Yong-Gang; LIU Mei

    2002-01-01

    By making use of the diagrammatic techniques in perturbation theory,we have investigated the Hall effect in a quasi-two-dimensional disordered electron system.In the weakly localized regime,the analytical expression for quantum correction to Hall conductivity has been obtained using the Kubo formalism and quasiclassical approximation.The relevant dimensional crossover behavior from three dimensions to two dimensions with decreasing the interlayer hopping energy is discussed.The quantum interference effect is shown to have a vanishing correction t,o the Hall coefficient.

  5. Kinetic Theory of a Confined Quasi-Two-Dimensional Gas of Hard Spheres

    Directory of Open Access Journals (Sweden)

    J. Javier Brey

    2017-02-01

    Full Text Available The dynamics of a system of hard spheres enclosed between two parallel plates separated a distance smaller than two particle diameters is described at the level of kinetic theory. The interest focuses on the behavior of the quasi-two-dimensional fluid seen when looking at the system from above or below. In the first part, a collisional model for the effective two-dimensional dynamics is analyzed. Although it is able to describe quite well the homogeneous evolution observed in the experiments, it is shown that it fails to predict the existence of non-equilibrium phase transitions, and in particular, the bimodal regime exhibited by the real system. A critical revision analysis of the model is presented , and as a starting point to get a more accurate description, the Boltzmann equation for the quasi-two-dimensional gas has been derived. In the elastic case, the solutions of the equation verify an H-theorem implying a monotonic tendency to a non-uniform steady state. As an example of application of the kinetic equation, here the evolution equations for the vertical and horizontal temperatures of the system are derived in the homogeneous approximation, and the results compared with molecular dynamics simulation results.

  6. An intrinsic growth instability in isotropic materials leads to quasi-two-dimensional nanoplatelets

    Science.gov (United States)

    Riedinger, Andreas; Ott, Florian D.; Mule, Aniket; Mazzotti, Sergio; Knüsel, Philippe N.; Kress, Stephan J. P.; Prins, Ferry; Erwin, Steven C.; Norris, David J.

    2017-07-01

    Colloidal nanoplatelets are atomically flat, quasi-two-dimensional sheets of semiconductor that can exhibit efficient, spectrally pure fluorescence. Despite intense interest in their properties, the mechanism behind their highly anisotropic shape and precise atomic-scale thickness remains unclear, and even counter-intuitive for commonly studied nanoplatelets that arise from isotropic crystal structures (such as zincblende CdSe and lead halide perovskites). Here we show that an intrinsic instability in growth kinetics can lead to such highly anisotropic shapes. By combining experimental results on the synthesis of CdSe nanoplatelets with theory predicting enhanced growth on narrow surface facets, we develop a model that explains nanoplatelet formation as well as observed dependencies on time and temperature. Based on standard concepts of volume, surface and edge energies, the resulting growth instability criterion can be directly applied to other crystalline materials. Thus, knowledge of this previously unknown mechanism for controlling shape at the nanoscale can lead to broader libraries of quasi-two-dimensional materials.

  7. Diffusivity and weak clustering in a quasi-two-dimensional granular gas.

    Science.gov (United States)

    Perera-Burgos, J A; Pérez-Ángel, G; Nahmad-Molinari, Y

    2010-11-01

    We present results from a detailed simulation of a quasi-two-dimensional dissipative granular gas, kept in a noncondensed steady state via vertical shaking over a rough substrate. This gas shows a weak power-law decay in the tails of its pair distribution functions, indicating clustering. This clustering depends monotonically on the dissipation coefficient and disappears when the sphere-sphere collisions are conservative. Clustering is also sensitive to the packing fraction. This gas also displays the standard nonequilibrium characteristics of similar systems, including non-Maxwellian velocity distributions. The diffusion coefficients are calculated over all the conditions of the simulations, and it is found that diluted gases are more diffusive for smaller restitution coefficients.

  8. Hydrodynamics for a model of a confined quasi-two-dimensional granular gas.

    Science.gov (United States)

    Brey, J Javier; Buzón, V; Maynar, P; García de Soria, M I

    2015-05-01

    The hydrodynamic equations for a model of a confined quasi-two-dimensional gas of smooth inelastic hard spheres are derived from the Boltzmann equation for the model, using a generalization of the Chapman-Enskog method. The heat and momentum fluxes are calculated to Navier-Stokes order, and the associated transport coefficients are explicitly determined as functions of the coefficient of normal restitution and the velocity parameter involved in the definition of the model. Also an Euler transport term contributing to the energy transport equation is considered. This term arises from the gradient expansion of the rate of change of the temperature due to the inelasticity of collisions, and it vanishes for elastic systems. The hydrodynamic equations are particularized for the relevant case of a system in the homogeneous steady state. The relationship with previous works is analyzed.

  9. Ordered quasi-two-dimensional structure of nanoparticles in semiflexible ring polymer brushes under compression

    Science.gov (United States)

    Hua, Yunfeng; Deng, Zhenyu; Jiang, Yangwei; Zhang, Linxi

    2017-06-01

    Molecular dynamics simulations of a coarse-grained bead-spring model of ring polymer brushes under compression are presented. Flexible polymer brushes are always disordered during compression, whereas semiflexible polymer brushes tend to be ordered under sufficiently strong compression. Further, the polymer monomer density of the semiflexible polymer brush is very high near the brush surface, inducing a peak value of the free energy near the surface. Therefore, when nanoparticles are compressed in semiflexible ring polymer brushes, they tend to exhibit a closely packed single-layer structure between the brush surface and the impenetrable wall, and a quasi-two-dimensional ordered structure near the brush surface is formed under strong compression. These findings provide a new approach to designing responsive applications.

  10. Origin of anomalous magnetic breakdown frequencies in quasi-two-dimensional organic conductors

    Science.gov (United States)

    Sandhu, P. S.; Kim, Ju H.; Brooks, J. S.

    1997-11-01

    We investigate the origin of anomalous magnetic breakdown frequencies in the de Haas-van Alphen (dHvA) effect in quasi-two-dimensional organic conductors such as α-(BEDT-TTF)2KHg(SCN)4 and κ-(BEDT-TTF)2Cu(NCS)2. A tight-binding model based on their realistic band structure is constructed and solved numerically to compute the field dependence of the magnetization. The present model provides a natural description for the phenomenon of magnetic breakdown between coexisting closed and open Fermi surfaces and accounts for the experimentally observed frequencies that are forbidden in the semiclassical picture. We find that the appearance of these anomalous frequencies in the dHvA signal is a quantum-mechanical effect which arises from differences in field dependence of the states in the two partially occupied bands near the Fermi level.

  11. Motility of Escherichia coli in a quasi-two-dimensional porous medium

    Science.gov (United States)

    Sosa-Hernández, Juan Eduardo; Santillán, Moisés; Santana-Solano, Jesús

    2017-03-01

    Bacterial migration through confined spaces is critical for several phenomena, such as biofilm formation, bacterial transport in soils, and bacterial therapy against cancer. In the present work, E. coli (strain K12-MG1655 WT) motility was characterized by recording and analyzing individual bacterium trajectories in a simulated quasi-two-dimensional porous medium. The porous medium was simulated by enclosing, between slide and cover slip, a bacterial-culture sample mixed with uniform 2.98-μ m -diameter spherical latex particles. The porosity of the medium was controlled by changing the latex particle concentration. By statistically analyzing several trajectory parameters (instantaneous velocity, turn angle, mean squared displacement, etc.), and contrasting with the results of a random-walk model developed ad hoc, we were able to quantify the effects that different obstacle concentrations have upon bacterial motility.

  12. Dynamical transition in a jammed state of a quasi-two-dimensional foam

    Science.gov (United States)

    Kurita, Rei; Furuta, Yujiro; Yanagisawa, Naoya; Oikawa, Noriko

    2017-06-01

    The states of foam are empirically classified into dry foam and wet foam by the volume fraction of the liquid. Recently, a transition between the dry foam state and the wet foam state has been found by characterizing the bubble shapes [Furuta et al., Sci. Rep. 6, 37506 (2016), 10.1038/srep37506]. In the literature, it is indirectly ascertained that the transition from the dry to the wet form is related to the onset of the rearrangement of the bubbles, namely, the liquid fraction at which the bubbles become able to move to replace their positions. The bubble shape is a static property, and the rearrangement of the bubbles is a dynamic property. Thus, we investigate the relation between the bubble shape transition and the rearrangement event occurring in a collapsing process of the bubbles in a quasi-two-dimensional foam system. The current setup brings a good advantage to observe the above transitions, since the liquid fraction of the foam continuously changes in the system. It is revealed that the rearrangement of the bubbles takes place at the dry-wet transition point where the characteristics of the bubble shape change.

  13. Valence and conduction band structure of the quasi-two-dimensional semiconductor Sn S2

    Science.gov (United States)

    Racke, David A.; Neupane, Mahesh R.; Monti, Oliver L. A.

    2016-02-01

    We present the momentum-resolved photoemission spectroscopy of both the valence and the conduction band region in the quasi-two-dimensional van der Waals-layered indirect band gap semiconductor Sn S2 . Using a combination of angle-resolved ultraviolet photoemission and angle-resolved two-photon photoemission (AR-2PPE) spectroscopy, we characterize the band structure of bulk Sn S2 . Comparison with density functional theory calculations shows excellent quantitative agreement in the valence band region and reveals several localized bands that likely originate from defects such as sulfur vacancies. Evidence for a moderate density of defects is also observed by AR-2PPE in the conduction band region, leading to localized bands not present in the computational results. The energetic structure and dispersion of the conduction bands is captured well by the computational treatment, with some quantitative discrepancies remaining. Our results provide a broader understanding of the electronic structure of Sn S2 in particular and van der Waals-layered semiconductors in general.

  14. General solution of the Dirac equation for quasi-two-dimensional electrons

    Energy Technology Data Exchange (ETDEWEB)

    Eremko, Alexander, E-mail: eremko@bitp.kiev.ua [Bogolyubov Institute for Theoretical Physics, Metrologichna Str., 14-b, Kyiv, 03680 (Ukraine); Brizhik, Larissa, E-mail: brizhik@bitp.kiev.ua [Bogolyubov Institute for Theoretical Physics, Metrologichna Str., 14-b, Kyiv, 03680 (Ukraine); Loktev, Vadim, E-mail: vloktev@bitp.kiev.ua [Bogolyubov Institute for Theoretical Physics, Metrologichna Str., 14-b, Kyiv, 03680 (Ukraine); National Technical University of Ukraine “KPI”, Peremohy av., 37, Kyiv, 03056 (Ukraine)

    2016-06-15

    The general solution of the Dirac equation for quasi-two-dimensional electrons confined in an asymmetric quantum well, is found. The energy spectrum of such a system is exactly calculated using special unitary operator and is shown to depend on the electron spin polarization. This solution contains free parameters, whose variation continuously transforms one known particular solution into another. As an example, two different cases are considered in detail: electron in a deep and in a strongly asymmetric shallow quantum well. The effective mass renormalized by relativistic corrections and Bychkov–Rashba coefficients are analytically obtained for both cases. It is demonstrated that the general solution transforms to the particular solutions, found previously (Eremko et al., 2015) with the use of spin invariants. The general solution allows to establish conditions at which a specific (accompanied or non-accompanied by Rashba splitting) spin state can be realized. These results can prompt the ways to control the spin degree of freedom via the synthesis of spintronic heterostructures with the required properties.

  15. Experimental Observation of Exact Coherent Structures in a Weakly Turbulent Quasi-Two-Dimensional Flow

    Science.gov (United States)

    Suri, Balachandra; Tithof, Jeffrey; Pallantla, Ravi Kumar; Grigoriev, Roman; Schatz, Michael

    2015-11-01

    The dynamical systems approach to fluid turbulence relies on understanding the role of unstable, non-chaotic solutions - such as equilibria, traveling waves, and periodic orbits - of the Navier-Stokes equations. These solutions, called Exact Coherent Structures, exist in the same parameter regime as turbulence, but being unstable, are observed in experiments only as short transients. In this talk, we present experimental evidence for the existence and dynamical relevance of unstable equilibria in a weakly turbulent quasi-two-dimensional (Q2D) Kolmogorov flow. In the experiment, this Q2D flow is generated in an electromagnetically driven shallow layer of electrolyte. The numerical simulations, however, use a strictly 2D model which incorporates the effects of the finite thickness of the fluid layer in the experiment. During its evolution, there are instances when the dynamics of a weakly turbulent flow slow down, rather dramatically. Using experimental flow fields from such instances, and by means of a Newton-Solver, we numerically compute several unstable equilibria. Additionally, using numerical simulations, we show that the dynamics of a turbulent flow in the neighbourhood of an equilibrium are accurately described by the unstable manifold of the equilibrium. This work is supported in part by the National Science Foundation under grants CBET-0900018, and CMMI-1234436.

  16. Vibrational properties of quasi-two-dimensional colloidal glasses with varying interparticle attraction.

    Science.gov (United States)

    Gratale, Matthew D; Ma, Xiaoguang; Davidson, Zoey S; Still, Tim; Habdas, Piotr; Yodh, A G

    2016-10-01

    We measure the vibrational modes and particle dynamics of quasi-two-dimensional colloidal glasses as a function of interparticle interaction strength. The interparticle attractions are controlled via a temperature-tunable depletion interaction. Specifically, the interparticle attraction energy is increased gradually from a very small value (nearly hard-sphere) to moderate strength (∼4k_{B}T), and the variation of colloidal particle dynamics and vibrations are concurrently probed. The particle dynamics slow monotonically with increasing attraction strength, and the particle motions saturate for strengths greater than ∼2k_{B}T, i.e., as the system evolves from a nearly repulsive glass to an attractive glass. The shape of the phonon density of states is revealed to change with increasing attraction strength, and the number of low-frequency modes exhibits a crossover for glasses with weak compared to strong interparticle attraction at a threshold of ∼2k_{B}T. This variation in the properties of the low-frequency vibrational modes suggests a new means for distinguishing between repulsive and attractive glass states.

  17. Anomalous metallic state in quasi-two-dimensional BaNiS2

    Science.gov (United States)

    Santos-Cottin, David; Gauzzi, Andrea; Verseils, Marine; Baptiste, Benoit; Feve, Gwendal; Freulon, Vincent; Plaçais, Bernard; Casula, Michele; Klein, Yannick

    2016-03-01

    We report on a systematic study of the thermodynamic, electronic, and charge transport properties of high-quality single crystals of BaNiS2, the metallic end member of the quasi-two-dimensional BaCo1 -xNixS2 system characterized by a metal-insulator transition at xc r=0.22 . Our analysis of magnetoresistivity and specific heat data consistently suggests a picture of compensated semimetal with two hole bands and one electron band, where electron-phonon scattering dominates charge transport and the minority holes exhibit, below ˜100 K, a very large mobility, μh˜15000 cm2V-1s-1 , which is explained by a Dirac-like band. Evidence of unconventional metallic properties is given by an intriguing crossover of the resistivity from a Bloch-Grüneisen regime to a linear-T regime occurring at 2 K and by a strong linear term in the paramagnetic susceptibility above 100 K. We discuss the possibility that these anomalies reflect a departure from conventional Fermi-liquid properties in presence of short-range AF fluctuations and of a large Hund coupling.

  18. Protected Fe valence in quasi-two-dimensional α-FeSi2

    Science.gov (United States)

    Miiller, W.; Tomczak, J. M.; Simonson, J. W.; Smith, G.; Kotliar, G.; Aronson, M. C.

    2015-05-01

    We report the first comprehensive study of the high temperature form (α-phase) of iron disilicide. Measurements of the magnetic susceptibility, magnetization, heat capacity and resistivity were performed on well characterized single crystals. With a nominal iron d6 configuration and a quasi-two-dimensional crystal structure that strongly resembles that of LiFeAs, α-FeSi2 is a potential candidate for unconventional superconductivity. Akin to LiFeAs, α-FeSi2 does not develop any magnetic order and we confirm its metallic state down to the lowest temperatures (T = 1.8 K). However, our experiments reveal that paramagnetism and electronic correlation effects in α-FeSi2 are considerably weaker than in the pnictides. Band theory calculations yield small Sommerfeld coefficients of the electronic specific heat γ = Ce/T that are in excellent agreement with experiment. Additionally, realistic many-body calculations further corroborate that quasi-particle mass enhancements are only modest in α-FeSi2. Remarkably, we find that the natural tendency to vacancy formation in the iron sublattice has little influence on the iron valence and the density of states at the Fermi level. Moreover, Mn doping does not significantly change the electronic state of the Fe ion. This suggests that the iron valence is protected against hole doping and indeed the substitution of Co for Fe causes a rigid-band like response of the electronic properties. As a key difference from the pnictides, we identify the smaller inter-iron layer spacing, which causes the active orbitals near the Fermi level to be of a different symmetry in α-FeSi2. This change in orbital character might be responsible for the lack of superconductivity in this system, providing constraints on pairing theories in the iron based pnictides and chalcogenides.

  19. On calculation of quasi-two-dimensional divergence-free projections for visualization of three-dimensional incompressible flows

    OpenAIRE

    Gelfgat, Alexander

    2015-01-01

    A visualization of three-dimensional incompressible flows by divergence-free quasi-two-dimensional projections of the velocity field on three coordinate planes was recently proposed. The projections were calculated using divergence-free Galerkin bases, which resulted in the whole procedure being complicated and CPU-time consuming. Here we propose an alternative way based on the Chorin projection combined with a SIMPLE-like iteration. The approach proposed is much easier in realization, allows...

  20. Mixed valence as a necessary criteria for quasi-two dimensional electron gas in oxide hetero-interfaces

    Science.gov (United States)

    Singh, Vijeta; Pulikkotil, J. J.

    2017-02-01

    The origin of quasi-two dimensional electron gas at the interface of polar-nonpolar oxide hetero-structure, such as LaAlO3/SrTiO3, is debated over electronic reconstruction and defects/disorder models. Common to these models is the partial valence transformation of substrate Ti ions from its equilibrium 4 + state to an itinerant 3 + state. Given that the Hf ions have a lower ionization potential than Ti due to the 4 f orbital screening, one would expect a hetero-interface conductivity in the polar-nonpolar LaAlO3/SrHfO3 system as well. However, our first principles calculations show the converse. Unlike the Ti3+ -Ti4+ valence transition which occur at a nominal energy cost, the barrier energy associated with its isoelectronic Hf3+ -Hf4+ counterpart is very high, hence suppressing the formation of quasi-two dimensional electron gas at LaAlO3/SrHfO3 hetero-interface. These calculations, therefore, emphasize on the propensity of mixed valence at the interface as a necessary condition for an oxide hetero-structure to exihibit quasi two-dimensional electron gas.

  1. Probing the Scale Invariance of the Inflationary Power Spectrum in Expanding Quasi-Two-Dimensional Dipolar Condensates

    Science.gov (United States)

    Chä, Seok-Yeong; Fischer, Uwe R.

    2017-03-01

    We consider an analogue de Sitter cosmos in an expanding quasi-two-dimensional Bose-Einstein condensate with dominant dipole-dipole interactions between the atoms or molecules in the ultracold gas. It is demonstrated that a hallmark signature of inflationary cosmology, the scale invariance of the power spectrum of inflaton field correlations, experiences strong modifications when, at the initial stage of expansion, the excitation spectrum displays a roton minimum. Dipolar quantum gases thus furnish a viable laboratory tool to experimentally investigate, with well-defined and controllable initial conditions, whether primordial oscillation spectra deviating from Lorentz invariance at trans-Planckian momenta violate standard predictions of inflationary cosmology.

  2. Visualization of three-dimensional incompressible flows by quasi-two-dimensional divergence-free projections in arbitrary flow regions

    Science.gov (United States)

    Gelfgat, Alexander Yu.

    2016-08-01

    A visualization of three-dimensional incompressible flows by divergence-free quasi-two-dimensional projections of the velocity field onto three coordinate planes is revisited. An alternative and more general way to compute the projections is proposed. The approach is based on the Chorin projection combined with a SIMPLE-like iteration. Compared to the previous methodology based on divergence-free Galerkin-Chebyshev bases, this technique, formulated in general curvilinear coordinates, is applicable to any flow region and allows for faster computations. To illustrate this visualization method, examples in Cartesian and spherical coordinates, as well as post-processing of experimental 3D-PTV data, are presented.

  3. Spin-Dependent Scattering Effects and Dimensional Crossover in a Quasi-Two-Dimensional Disordered Electron System

    Institute of Scientific and Technical Information of China (English)

    YANG YongHong; WANG YongGang; LIU Mei; WANG Jin

    2002-01-01

    Two kinds of spin-depcndcnt scattering effects (magnetic-iinpurity and spin-orbit scatterings) axe investi-gated theoretically in a quasi-two-dimensional (quasi-2D) disordered electron system. By making use of the diagrammatictechniques in perturbation theory, we have calculated the dc conductivity and magnetoresistance due to weak-localizationeffects, the analytical expressions of them are obtained as functions of the interlayer hopping energy and the charac-teristic times: elastic, inelastic, magnetic and spin-orbit scattering times. The relevant dimensional crossover behaviorfrom 3D to 2D with decreasing the interlayer coupling is discussed, and the condition for the crossover is shown to bedependent on the aforementioned scattering times. At low temperature there exists a spin-dcpendent-scattering-induccddimensional crossover in this system.

  4. On calculation of quasi-two-dimensional divergence-free projections for visualization of three-dimensional incompressible flows

    CERN Document Server

    Gelfgat, Alexander

    2015-01-01

    A visualization of three-dimensional incompressible flows by divergence-free quasi-two-dimensional projections of the velocity field on three coordinate planes was recently proposed. The projections were calculated using divergence-free Galerkin bases, which resulted in the whole procedure being complicated and CPU-time consuming. Here we propose an alternative way based on the Chorin projection combined with a SIMPLE-like iteration. The approach proposed is much easier in realization, allows for faster computations, and can be generalized for arbitrary curvilinear orthogonal coordinates. To illustrate the visualization method, examples of flow visualization in cylindrical and spherical coordinates, as well as post-processing of experimental 3D-PTV data are presented.

  5. Magnetic breakdown phenomenon in quasi-two-dimensional organic conductors: A quantum model inspired by a realistic band structure

    Science.gov (United States)

    Kim, Ju H.; Han, S. Y.; Brooks, J. S.

    1999-08-01

    We investigate the phenomenon of magnetic breakdown in quasi-two-dimensional organic conductors such as α-(ET)2KHg(SCN)4 and κ-(ET)2Cu(NCS)2 by constructing a tight-binding model based on a realistic band structure which is derived from the crystallographic data. We solve the model numerically to compute the magnetic field dependence of the magnetization and show that the present model accounts naturally for the experimentally observed magnetization oscillation frequencies that are forbidden in the semiclassical picture. The computed values of the fundamental and magnetic breakdown frequencies with no adjustable parameters are close to the experimentally measured values. For completeness, we carry out the computation for both canonical (fixed number of particles) and grand canonical (fixed chemical potential) ensembles, and show that the forbidden frequencies appear in both cases. Hence, the appearance of anomalous frequencies in the de Haas-van Alphen effect has a quantum-mechanical origin and arises from the interplay of electronic states from two partially occupied bands near the Fermi energy as a function of magnetic field. We also compute the temperature dependence of the magnetization and apply ad hoc the Lifshitz-Kosevich analysis to the amplitudes of the Fourier components at moderately high temperatures. This yields effective mass values for α-(ET)2KHg(SCN)4 in good agreement with experimental values.

  6. Axis and velocity determination for quasi two-dimensional plasma/field structures from Faraday's law: A second look

    Science.gov (United States)

    Sonnerup, Bengt U. Ö.; Denton, Richard E.; Hasegawa, Hiroshi; Swisdak, M.

    2013-05-01

    We re-examine the basic premises of a single-spacecraft data analysis method, developed by Sonnerup and Hasegawa (2005), for determining the axis orientation and proper frame velocity of quasi two-dimensional, quasi-steady structures of magnetic field and plasma. The method, which is based on Faraday's law, makes use of magnetic and electric field data measured by a single spacecraft traversing the structure, although in many circumstances the convection electric field, - v × B, can serve as a proxy for E. It has been used with success for flux ropes observed at the magnetopause but has usually failed to provide acceptable results when applied to real space data from reconnection events as well as to virtual data from numerical MHD simulations of such events. In the present paper, the reasons for these shortcomings are identified, analyzed, and discussed in detail. Certain basic properties of the method are presented in the form of five theorems, the last of which makes use of singular value decomposition to treat the special case where the magnetic variance matrix is non-invertible. These theorems are illustrated using data from analytical models of flux ropes and also from MHD simulations as well as a 2-D kinetic simulation of reconnection. The results make clear that the method requires the presence of a significant, non-removable electric field distribution in the plane transverse to the invariant direction and that it is sensitive to deviations from strict two-dimensionality and strict time stationarity.

  7. Evolution of the vortex state in the BCS-BEC crossover of a quasi two-dimensional superfluid Fermi gas

    Science.gov (United States)

    Luo, Xuebing; Zhou, Kezhao; Zhang, Zhidong

    2016-11-01

    We use the path-integral formalism to investigate the vortex properties of a quasi-two dimensional (2D) Fermi superfluid system trapped in an optical lattice potential. Within the framework of mean-field theory, the cooper pair density, the atom number density, and the vortex core size are calculated from weakly interacting BCS regime to strongly coupled while weakly interacting BEC regime. Numerical results show that the atoms gradually penetrate into the vortex core as the system evolves from BEC to BCS regime. Meanwhile, the presence of the optical lattice allows us to analyze the vortex properties in the crossover from three-dimensional (3D) to 2D case. Furthermore, using a simple re-normalization procedure, we find that the two-body bound state exists only when the interaction is stronger than a critical one denoted by G c which is obtained as a function of the lattice potential’s parameter. Finally, we investigate the vortex core size and find that it grows with increasing interaction strength. In particular, by analyzing the behavior of the vortex core size in both BCS and BEC regimes, we find that the vortex core size behaves quite differently for positive and negative chemical potentials. Project supported by the National Natural Science Foundation of China (Grant Nos. 51331006, 51590883, and 11204321) and the Project of Chinese Academy of Sciences (Grant No. KJZD-EW-M05-3).

  8. Size-Dependent Biexciton Quantum Yields and Carrier Dynamics of Quasi-Two-Dimensional Core/Shell Nanoplatelets.

    Science.gov (United States)

    Ma, Xuedan; Diroll, Benjamin T; Cho, Wooje; Fedin, Igor; Schaller, Richard D; Talapin, Dmitri V; Gray, Stephen K; Wiederrecht, Gary P; Gosztola, David J

    2017-09-05

    Quasi-two-dimensional nanoplatelets (NPLs) possess fundamentally different excitonic properties from zero-dimensional quantum dots. We study lateral size-dependent photon emission statistics and carrier dynamics of individual NPLs using second-order photon correlation (g((2))(τ)) spectroscopy and photoluminescence (PL) intensity-dependent lifetime analysis. Room-temperature radiative lifetimes of NPLs can be derived from maximum PL intensity periods in PL time traces. It first decreases with NPL lateral size and then stays constant, deviating from the electric dipole approximation. Analysis of the PL time traces further reveals that the single exciton quantum yield in NPLs decreases with NPL lateral size and increases with protecting shell thickness, indicating the importance of surface passivation on NPL emission quality. Second-order photon correlation (g((2))(τ)) studies of single NPLs show that the biexciton quantum yield is strongly dependent on the lateral size and single exciton quantum yield of the NPLs. In large NPLs with unity single exciton quantum yield, the corresponding biexciton quantum yield can reach unity. These findings reveal that by careful growth control and core-shell material engineering, NPLs can be of great potential for light amplification and integrated quantum photonic applications.

  9. Effects of anisotropy and magnetic fields on the specific heat of a quasi-two-dimensional Boltzmann gas in an elliptical parabolic quantum dot

    Institute of Scientific and Technical Information of China (English)

    Zhai Zhi-Yuan; Li Yu-Qi; Pan Xiao-Yin

    2012-01-01

    We investigate the effects due to anisotropy and magnetic field interaction for a quasi-two-dimensional Boltzmann gas in an elliptical parabolic quantum dot.The specific heat is studied with varying temperature,anisotropy,and magnetic field strength.The cases without and with the inclusion of the spin Zeeman interaction are considered.

  10. Nuclear-magnetic-resonance relaxation due to the translational diffusion of fluid confined to quasi-two-dimensional pores

    Science.gov (United States)

    Faux, D. A.; McDonald, P. J.; Howlett, N. C.

    2017-03-01

    Nuclear-magnetic-resonance (NMR) relaxation experimentation is an effective technique for nondestructively probing the dynamics of proton-bearing fluids in porous media. The frequency-dependent relaxation rate T1-1 can yield a wealth of information on the fluid dynamics within the pore provided data can be fit to a suitable spin diffusion model. A spin diffusion model yields the dipolar correlation function G (t ) describing the relative translational motion of pairs of 1H spins which then can be Fourier transformed to yield T1-1. G (t ) for spins confined to a quasi-two-dimensional (Q2D) pore of thickness h is determined using theoretical and Monte Carlo techniques. G (t ) shows a transition from three- to two-dimensional motion with the transition time proportional to h2. T1-1 is found to be independent of frequency over the range 0.01-100 MHz provided h ≳5 nm and increases with decreasing frequency and decreasing h for pores of thickness h <3 nm. T1-1 increases linearly with the bulk water diffusion correlation time τb allowing a simple and direct estimate of the bulk water diffusion coefficient from the high-frequency limit of T1-1 dispersion measurements in systems where the influence of paramagnetic impurities is negligible. Monte Carlo simulations of hydrated Q2D pores are executed for a range of surface-to-bulk desorption rates for a thin pore. G (t ) is found to decorrelate when spins move from the surface to the bulk, display three-dimensional properties at intermediate times, and finally show a bulk-mediated surface diffusion (Lévy) mechanism at longer times. The results may be used to interpret NMR relaxation rates in hydrated porous systems in which the paramagnetic impurity density is negligible.

  11. Fingerprints of field-induced Berezinskii-Kosterlitz-Thouless transition in quasi-two-dimensional S=1/2 Heisenberg magnets Cu(en)(H2O)2SO4 and Cu(tn)Cl2

    Science.gov (United States)

    Baranová, Lucia; Orendáčová, Alžbeta; Čižmár, Erik; Tarasenko, Róbert; Tkáč, Vladimír; Orendáč, Martin; Feher, Alexander

    2016-04-01

    Organo-metallic compounds Cu(en)(H2O)2SO4 (en=C2H8N2) and Cu(tn)Cl2 (tn=C3H10N2) representing S=1/2 quasi-two-dimensional Heisenberg antiferromagnets with an effective intra-layer exchange coupling J/kB≈3 K, have been examined by specific heat measurements at temperatures down to nominally 50 mK and magnetic fields up to 14 T. A comparative analysis of magnetic specific heat in zero magnetic field revealed nearly identical contribution of short-range magnetic correlations and significant differences were observed at lowest temperatures. A phase transition to long-range order was observed in Cu(en)(H2O)2SO4 at TC=0.9 K while hidden in Cu(tn)Cl2. A response of both compounds to the application of magnetic field has rather universal features characteristic for a field-induced Berezinskii-Kosterlitz-Thouless transition theoretically predicted for ideal two-dimensional magnets.

  12. Binary cooperative NiCo2O4 on the nickel foams with quasi-two-dimensional precursors: a bridge between 'supercapacitor' and 'battery' in electrochemical energy storage.

    Science.gov (United States)

    Peng, Tao; Qian, Zhongyu; Wang, Jun; Qu, Liangti; Wang, Peng

    2015-02-28

    Some inorganic quasi-two-dimensional nanomaterials such as cobalt-nickel hydroxides are kinetically facile for a capacitive charge storage process. However, high performance capacitive charge storage needs a balance of the ionic and electronic transporting, and to build up an integrated architecture on substrates step by step and utilize the interface better is still a key challenge. As the interfacial assembly has conflicted with our goals for high-performance capacitive charge storage process, we identify theoretically and experimentally binary cooperative nanoscale interfacial materials to solve the problem. Co-Ni-hydroxide precursors were prepared by hybrid quasi-two-dimensional nanosheets and hetero-oriented nanocrystallines walls. Followed by dip-dry and annealing, NiCo2O4 could adhere to the nickel foams robustly with a solution-based surface treatment. Moreover, an unusual phenomenon in the electrochemical test inspired us to establish a bridge between 'supercapacitor' and 'battery'. The bridged gap highlights a new design idea for high-performance energy storage.

  13. Linear stability of horizontal, laminar fully developed, quasi-two-dimensional liquid metal duct flow under a transverse magnetic field and heated from below

    Science.gov (United States)

    Vo, Tony; Pothérat, Alban; Sheard, Gregory J.

    2017-03-01

    This study considers the linear stability of Poiseuille-Rayleigh-Bénard flows subjected to a transverse magnetic field, to understand the instabilities that arise from the complex interaction between the effects of shear, thermal stratification, and magnetic damping. This fundamental study is motivated in part by the desire to enhance heat transfer in the blanket ducts of nuclear fusion reactors. In pure magnetohydrodynamic flows, the imposed transverse magnetic field causes the flow to become quasi-two-dimensional and exhibit disturbances that are localized to the horizontal walls. However, the vertical temperature stratification in Rayleigh-Bénard flows feature convection cells that occupy the interior region, and therefore the addition of this aspect provides an interesting point for investigation. The linearized governing equations are described by the quasi-two-dimensional model proposed by Sommeria and Moreau [J. Fluid Mech. 118, 507 (1982), 10.1017/S0022112082001177], which incorporates a Hartmann friction term, and the base flows are considered fully developed and one-dimensional. The neutral stability curves for critical Reynolds and Rayleigh numbers, Rec and Rac, respectively, as functions of Hartmann friction parameter H have been obtained over 10-2≤H ≤104 . Asymptotic trends are observed as H →∞ following Rec∝H1 /2 and Rac∝H . The linear stability analysis reveals multiple instabilities which alter the flow both within the Shercliff boundary layers and the interior flow, with structures consistent with features from plane Poiseuille and Rayleigh-Bénard flows.

  14. Electronic band structure and Fermi surfaces of the quasi-two-dimensional monophosphate tungsten bronze, P4W12O44

    Science.gov (United States)

    Paul, S.; Ghosh, A.; Sato, T.; Sarma, D. D.; Takahashi, T.; Wang, E.; Greenblatt, M.; Raj, S.

    2014-02-01

    The electronic structure of quasi-two-dimensional monophosphate tungsten bronze, P4W12O44, has been investigated by high-resolution angle-resolved photoemission spectroscopy and density functional theoretical calculations. Experimental electron-like bands around \\Gamma point and Fermi surfaces have similar shapes as predicted by calculations. Fermi surface mapping at different temperatures shows a depletion of density of states at low temperature in certain flat portions of the Fermi surfaces. These flat portions of the Fermi surfaces satisfy the partial nesting condition with incommensurate nesting vectors q_1 and q_2 , which leads to the formation of charge density waves in this phosphate tungsten bronzes. The setting up of charge density wave in these bronzes can well explain the anomaly observed in its transport properties.

  15. Non-Linear Conduction in the Density Wave State of Quasi-Two Dimensional Organic Conductor α-(BEDT-TTF)2KHg(SCN)4

    Science.gov (United States)

    Fujita, Toshiyuki; Sasaki, Takahiko; Yoneyama, Naoki; Kobayashi, Norio

    2004-06-01

    Current-voltage characteristics are measured in the quasi-two dimensional organic conductor α-(BEDT-TTF)2KHg(SCN)4 at temperatures down to 0.5 K and in the magnetic field up to 25 T. The non-linear conduction with a threshold electric field is found in the density wave state. The features of threshold electric field obtained in the low magnetic field region are explained by the unconventional charge density wave model. In the high magnetic field region, where the Shubnikov-de Haas oscillations appear, the current-voltage characteristics reveal that the density wave state synchronizes with the filling of the electron on the Landau level and continues even above a kink field 23 T.

  16. Drude weight in quasi-two-dimensional organic conductors close to the Mott transition: Optical studies of the bandwidth, filling and temperature dependence

    Energy Technology Data Exchange (ETDEWEB)

    Drichko, Natalia [Ioffe Physico-Technical Institute, Polytekhnicheskaya 26, 194021 St. Petersburg (Russian Federation); 1. Physikalisches Institut, Universitaet Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart (Germany)], E-mail: drichko@pi1.physik.uni-stuttgart.de; Dumm, Michael; Faltermeier, Daniel; Dressel, Martin [1. Physikalisches Institut, Universitaet Stuttgart, Pfaffenwaldring 57, 70550 Stuttgart (Germany); Merino, Jaime [Dept. de Fisica Teorica de la Materia Condensada, Universidad Autonoma de Madrid (Spain); Greco, Andres [Facultad de Ciencias Exactas Ingenieria y Agrimensura e Instituto de Fisica Rosario (UNR-CONICET), Rosario (Argentina)

    2007-09-01

    We explore the effects of electronic correlations in quasi-two-dimensional BEDT-TTF-based organic conductors with half, quarter and 1/5-filled bands. Close to the Mott transition but still on the metallic side, quasiparticles are observed in the 1/2-filled systems only at temperatures well below 100 K, with a considerable growth of the Drude-like contribution. In contrast, the 1/4-filled conductors show a zero-frequency conduction peak already at room temperature which increases slightly upon cooling. Basically no change with temperature is observed for the Drude contribution of the 1/5-filled compound. Optical studies allow us to investigate the formation of quasiparticles at low temperature for systems of different filling. The strongest effect is observed in 1/2-filled compounds, it becomes weaker in 1/4 filled, while in the 1/5-filled compound no change of the Dude-peak on temperature is seen.

  17. Magnetic ground state of quasi-two-dimensional organic conductor, τ-(EDO-S,S-DMEDT-TTF)2(AuCl2)1+y

    Science.gov (United States)

    Nakanishi, T.; Yasuzuka, S.; Yoshino, H.; Fujiwara, H.; Sugimoto, T.; Nishio, Y.; Kajita, K.; Anyfantis, G. A.; Papavassiliou, G. C.; Murata, K.

    2006-11-01

    To understand the interplay between transport and magnetic properties, quasi-two-dimensional (Q2D) organic conductor τ-(EDO-S,S-DMEDTTTF)2(AuCl2)1+y was studied by measurements of electric resistivity ( ρa, ρc), magnetoresistance (MR), susceptibility (χ) and specific heat (C) in the temperature region between 1 K and 300 K. In spite of the fact that the drastic changes were observed in ρa, ρc, MR and χ at TC = 20 K, no anomaly was seen in C. The concentration of spins estimated from M-H curve is about 360 ppm, which is difficult to detect anomaly in C. These data suggest that the number of spins is very small in the ground state like spin-glass system.

  18. Near-degeneracy of extended s +dx2-y2 and dx y order parameters in quasi-two-dimensional organic superconductors

    Science.gov (United States)

    Guterding, Daniel; Altmeyer, Michaela; Jeschke, Harald O.; Valentí, Roser

    2016-07-01

    The symmetry of the superconducting order parameter in quasi-two-dimensional bis-ethylenedithio-tetrathiafulvalene (BEDT-TTF) organic superconductors is a subject of ongoing debate. We report ab initio density-functional-theory calculations for a number of organic superconductors containing κ -type layers. Using projective Wannier functions, we derive the parameters of a common low-energy Hamiltonian based on individual BEDT-TTF molecular orbitals. In a random-phase approximation spin-fluctuation approach, we investigate the evolution of the superconducting pairing symmetry within this model, and we point out a phase transition between extended s +dx2-y2 and dx y symmetry. We discuss the origin of the mixed order parameter and the relation between the realistic molecule description and the widely used dimer approximation. Based on our ab initio calculations, we position the investigated materials in the obtained molecule model phase diagram, and we simulate scanning tunneling spectroscopy experiments for selected cases. Our calculations show that many κ -type materials lie close to the phase-transition line between the two pairing symmetry types found in our calculation, possibly explaining the multitude of contradictory experiments in this field.

  19. Interplay between Ferroelastic and Metal-Insulator Phase Transitions in Strained Quasi-Two-Dimensional VO2 Nanoplatelets

    Energy Technology Data Exchange (ETDEWEB)

    Tselev, Alexander [ORNL; Strelcov, Evgheni [Southern Illinois University; Luk' yanchuk, Prof. Igor A. [University of Picardie Jules Verne, Amiens, France; Ivanov, Ilia N [ORNL; Budai, John D [ORNL; Tischler, Jonathan Zachary [ORNL; Jones, Keith M [ORNL; Proksch, Roger [Asylum Research, Santa Barbara, CA; Kalinin, Sergei V [ORNL; Kolmakov, Andrei [ORNL

    2010-01-01

    Formation of ferroelastic twin domains in VO_2 nanosystems can strongly affect local strain distributions, and hence couple to the strain-controlled metal-insulator transition. Here we report polarized-light optical and scanning microwave microscopy studies of interrelated ferroelastic and metal-insulator transitions in single-crystalline vanadium dioxide (VO_2) quasi-two-dimensional (quasi-2D) nanoplatelets (NPls). In contrast to quasi-1D single-crystalline nanobeams, the geometric frustration results in emergence of several possible families of ferroelastic domains in NPls, thus allowing systematic studies of strain-controlled transitions in the presence of geometrical frustration. We demonstrate possibility of controlling the ferroelastic domain population by the strength of the NPl-substrate interaction, mechanical stress, and by the NPl lateral size. Ferroelastic domain species and domain walls are identified based on standard group-theoretical considerations. Using variable temperature microscopy, we imaged the development of domains of metallic and semiconducting phases during the metal-insulator phase transition and non-trivial strain-driven reentrant domain formation. A long-range reconstruction of ferroelastic structures accommodating metal-insulator domain formation has been observed. These studies illustrate that complete picture of the phase transitions in single-crystalline and disordered VO_2 structures can be drawn only if both ferroelastic and metal-insulator strain effects are taken into consideration and understood.

  20. Quasi-two-dimensional subthreshold current model of deep submicrometer SOI drive-in gate controlled hybrid transistors with lateral non-uniform doping profile

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    We have analyzed the operating mechanism of the novel deep submicrometer SOI drive-in gate controlled hybrid transistor (DGCHT), which can effectively alleviate the contradiction between speed enhancement and power reduction in conventional MOS devices and can improve the output resistance. On the basis of this, the subthreshold current model of DGCHTs is proposed. The model takes into account the impact of lateral non-uniform doping profile on body effect, short-channel effect and carrier mobility. Considering the mobile charge, two-dimensional Poisson equation is solved with quasi-two-dimensional analysis and parabolic approximation of surface potential. With the surface potential obtained, the subthreshold current is figured out, including both the diffusion and drift component. The calculated results are in good agreement with the MEDICI numerical simulation results, indicating the correct description of the current characteristics of SOI DGCHT by the presented model. The model can also be considered as an important reference to the current simulation of deep submicrometer MOSFET with pocket implantation.

  1. H-T phase diagram and the nature of vortex-glass phase in a quasi-two-dimensional superconductor: Sn-metal layer sandwiched between graphene sheets

    Energy Technology Data Exchange (ETDEWEB)

    Suzuki, Masatsugu; Suzuki, Itsuko S.; Walter, Juergen

    2004-02-15

    The magnetic properties of a quasi-two-dimensional (2D) superconductor, Sn-metal graphite (MG), are studied using DC and AC magnetic susceptibility. Sn-MG has a unique layered structure where Sn metal layer is sandwiched between adjacent graphene sheets. This compound undergoes a superconducting transition at T{sub c}=3.75 K at H=0. The H-T diagram of Sn-MG is similar to that of a quasi-2D superconductors. The phase boundaries of vortex liquid, vortex glass, and vortex lattice phase merge into a multicritical point located at T*=3.4 K and H*=40 Oe. There are two irreversibility lines denoted by H{sub gl} (de Almeida-Thouless type) and H{sub gl{sup '}} (Gabay-Toulouse type), intersecting at T{sub 0}{sup '}=2.5 K and H{sub 0}{sup '}=160 Oe. The nature of slow dynamic and nonlinearity of the vortex glass phase is studied.

  2. Quasi-two-dimensional Bose-Einstein condensation of spin triplets in the dimerized quantum magnet Ba2CuSi2O6Cl2

    Science.gov (United States)

    Okada, Makiko; Tanaka, Hidekazu; Kurita, Nobuyuki; Johmoto, Kohei; Uekusa, Hidehiro; Miyake, Atsushi; Tokunaga, Masashi; Nishimoto, Satoshi; Nakamura, Masaaki; Jaime, Marcelo; Radtke, Guillaume; Saúl, Andrés

    2016-09-01

    We synthesized single crystals of composition Ba2CuSi2O6Cl2 and investigated their quantum magnetic properties. The crystal structure is closely related to that of the quasi-two-dimensional (2D) dimerized magnet BaCuSi2O6 also known as Han purple. Ba2CuSi2O6Cl2 has a singlet ground state with an excitation gap of Δ /kB=20.8 K. The magnetization curves for two different field directions almost perfectly coincide when normalized by the g factor except for a small jump anomaly for a magnetic field perpendicular to the c axis. The magnetization curve with a nonlinear slope above the critical field is in excellent agreement with exact-diagonalization calculations based on a 2D coupled spin-dimer model. Individual exchange constants are also evaluated using density functional theory (DFT). The DFT results demonstrate a 2D exchange network and weak frustration between interdimer exchange interactions, supported by weak spin-lattice coupling implied from our magnetostriction data. The magnetic-field-induced spin ordering in Ba2CuSi2O6Cl2 is described as the quasi-2D Bose-Einstein condensation of triplets.

  3. Synthesis and Structure of A Novel Quasi-Two Dimensional Organic-inorganic Hybrid Coordination Polymer:{[Cu(en)2][Ag2I4]}n

    Institute of Scientific and Technical Information of China (English)

    SUN Ling-Guo; LI Hao-Hong; CHEN Zhi-Rong; HUANG Chang-Cang; ZHAO Bin; LI Jun-Qian

    2006-01-01

    A novel coordination polymer {[Cu(en)2][Ag2I4]}n (en = ethylenediamine) was synthesized by the reaction of NaAgI2 and Cu(en)2(NO3)2·2H2O at room temperature with pH = 6.0, and the structure was characterized by X-ray single-crystal diffraction. It crystallizes in monoclinic, space group C2/m, with a=10.646(2), b = 13.304(3), c = 6.8445(14)(A), β = 118.95(3)°, C4H16N4CuAg2I4, Mr = 907.10, V = 848.3(4)(A)3, Z = 2, Dc = 3.551 g/cm3, F(000) = 806, μ(MoKα) = 10.787 mm(1, the final R1 = 0.0256 and wR2 = 0.0654 for 900 observed reflections with I > 2σ(I). According to structural analysis, the title compound consists of template cation [Cu(en)2]2+ and inorganic chain [Ag2I4]n2-. The polymeric negative chain [Ag2I4]n2- is built up from pairs of AgI4 tetrahedron by sharing one edge. Through N-H…I hydrogen-bonding interactions, the whole structure represents a quasi-two dimensional arrangement. Electrostatic attraction exists between organic cations and inorganic chains, leading to a so-called organic-inorganic hybrid structure.

  4. Optical investigation of the quasi-two-dimensional Mott system Ca_2-xSr_xRuO4 (0.0<= x<= 2.0)

    Science.gov (United States)

    Lee, J. S.; Noh, T. W.; Lee, Y. S.; Oh, S.-J.; Nakatsuji, S.; Maeno, Y.

    2002-03-01

    The doping and temperature dependent optical conductivity spectra σ (ω ) in the ab-plane of the quasi-two-dimensional system Ca_2-xSr_xRuO4 (0.0= 0.2, the σ (ω ) show features of the Mott-Hubbard system. However, the insulating spectra of x=0.00 and 0.06 show an unusual two-peak structure around 1.0 and 2.0 eV. From the systematic changes with doping, it was found that both excitations have the correlation-induced Ru 4 d characters. Interestingly, for the x=0.06 sample, softening of the streching phonon mode and strong spectral weight redistribution between these two peaks were observed with decreasing temperature. These could be understood by the orbital occupancy changes with the RuO6 octahedral flattening. Possible connections to the critical behaviors of the specific heat and susceptibility at x=0.5 will be also discussed.

  5. Quasi-two-dimensional superconductivity in FeSe0.3Te0.7 thin films and electric-field modulation of superconducting transition.

    Science.gov (United States)

    Lin, Zhu; Mei, Chenguang; Wei, Linlin; Sun, Zhangao; Wu, Shilong; Huang, Haoliang; Zhang, Shu; Liu, Chang; Feng, Yang; Tian, Huanfang; Yang, Huaixin; Li, Jianqi; Wang, Yayu; Zhang, Guangming; Lu, Yalin; Zhao, Yonggang

    2015-09-18

    We report the structural and superconducting properties of FeSe0.3Te0.7 (FST) thin films with different thicknesses grown on ferroelectric Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates. It was shown that the FST films undergo biaxial tensile strains which are fully relaxed for films with thicknesses above 200 nm. Electrical transport measurements reveal that the ultrathin films exhibit an insulating behavior and superconductivity appears for thicker films with Tc saturated above 200 nm. The current-voltage curves around the superconducting transition follow the Berezinskii-Kosterlitz-Thouless (BKT) transition behavior and the resistance-temperature curves can be described by the Halperin-Nelson relation, revealing quasi-two-dimensional phase fluctuation in FST thin films. The Ginzburg number decreases with increasing film thickness indicating the decrease of the strength of thermal fluctuations. Upon applying electric field to the heterostructure, Tc of FST thin film increases due to the reduction of the tensile strain in FST. This work sheds light on the superconductivity, strain effect as well as electric-field modulation of superconductivity in FST films.

  6. Excitations and spin correlations near the interface of two three-dimensional Heisenberg antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Voropajeva, N., E-mail: niina.voropajeva@ut.ee [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia); Sherman, A., E-mail: alexei@fi.tartu.ee [Institute of Physics, University of Tartu, Riia 142, 51014 Tartu (Estonia)

    2012-09-03

    Magnetic excitations and spin correlations near the interface of two spin-1/2 Heisenberg antiferromagnets are considered using the spin-wave approximation. When the interaction between boundary spins differs essentially from exchange constants inside the antiferromagnets, quasi-two-dimensional spin waves appear in the near-boundary region. They eject bulk magnons from this region, thereby dividing the antiferromagnets into areas with different magnetic excitations. The decreased dimensionality of the near-boundary modes leads to amplified nearest-neighbor spin correlations in the interface area. -- Highlights: ► Excitations near the interface of two Heisenberg antiferromagnets are considered. ► Different quasi-two-dimensional spin waves may appear in the interface region. ► The interface modes eject bulk modes from the near-boundary region. ► The interface modes produce amplified spin correlations near the boundary.

  7. Intrinsic magnetization in the novel quasi-two-dimensional superconducting and magnetic Fe1+δTe1-xSex system

    Science.gov (United States)

    Yoshimura, Kazuyoshi; Michioka, Chishiro; Matsui, Mami; Ohta, Hiroto; Yang, Jinhu; Fang, Minghu

    2011-06-01

    Intrinsic spin susceptibility of the novel layered superconducting and magnetic system Fe1+δTe1-xSex was investigated by means of the magnetization measurements in comparing with the 125Te NMR Knight shift 125K. The macroscopic uniform susceptibility in Fe1+δTe1-xSex consists of the itinerant magnetization originated in the Fe(1) site, localized one in the Fe(2) site and the ferromagnetic-like impurity which is frequently sandwiched by the thin film-like single crystals. Unlike the macroscopic magnetization, Knight shift 125K is mainly attributed to the itinerant magnetism of the Fe(1) site, which is important for the superconductivity and the magnetism in the Fe1+δTe1-xSex system. The magnetic susceptibility estimated in the high-field region agrees well with 125K. The uniform susceptibility of the superconducting Fe1+δTe1-xSex gradually decreases with decreasing temperature in the normal state accompanied by the growth of antiferromagnetic spin afluctuations.

  8. Evidence for the quasi-two dimensional behavior of the vortex structure in Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Pastoriza, H. (Comision Nacional de Energia Atomica, Centro Atomico Bariloche (Argentina)); Arribere, A. (Comision Nacional de Energia Atomica, Centro Atomico Bariloche (Argentina)); Goffman, M.F. (Comision Nacional de Energia Atomica, Centro Atomico Bariloche (Argentina)); Cruz, F. de la (Comision Nacional de Energia Atomica, Centro Atomico Bariloche (Argentina)); Mitzi, D.B. (Dept. of Applied Physics, Stanford Univ., CA (United States)); Kapitulnik, A. (Dept. of Applied Physics, Stanford Univ., CA (United States))

    1994-02-01

    AC susceptibility and dc magnetization measurements on Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] (BSCCO) single crystals in a wide range of temperatures clearly show that below the dc irreversibility line the vortex system loss the long range order in the c direction. The susceptibility data taken at 7 Hz show the different nature of two dissipation peaks: One related to the interplane currents at temperatures well below the dc irreversibility line and the other associated with the intraplane ones at temperatures above that line. In this sense the irreversibility line corresponds to the temperature where quasi-two dimensional vortices are depinned. (orig.)

  9. Chemical synthesis and assembly of quasi-two-dimensional metal chalcogenides graphene analogues%准二维金属硫属化合物类石墨烯结构的化学合成与组装

    Institute of Scientific and Technical Information of China (English)

    冯冯; 冯骏; 吴长征; 谢毅

    2012-01-01

    Inorganic graphene analogues are regarded as a typical quasi-two-dimensional nanostructure system. Graphene analogues entail more structural parameters that could be controlled compared with the pure-carbon graphene, which leads to the well controlled energy-band type and gap width, showing the promising signs in constructing electronic device in the field of energy conversion and energy storage. In this regard, metal chalcogenides (MCs) have drawn extensive attention as an important graphene analogue material system due to its unique quasi-two dimensional crystallographic structure. Herein, we reviewed the synthesis and assembly methodologies for graphene analogues of MCs, as well as their functional applications of their assembled nanostructures. We put forward the strategies that utilizing chemical methods to weaken interlayer force and embodying the highly anisotropic characteristics in the internal structural lattices to successfully realize the fabrication of graphene analogues. Finally, we also summarized the assembly strategy of graphene analogues and their promising applications in the area of energy storage and intelligent responsiveness nanodevices.%无机类石墨烯属于准二维纳米结构体系,因其具有比纯碳石墨烯本身更多的调控参数,比如带隙类型及其带隙宽度可调节等,在电子器件构筑和能量转化存储等领域有着重要的科学意义和广阔的应用前景.近年来,具有准二维特征的金属硫属化合物(metal chalcogenides,MCs)作为类石墨烯结构的重要材料体系受到了广泛关注.本文概述了近年来金属硫属化合物类石墨烯结构的化学制备方法及其可能的组装应用,提出了通过系列方法影响层间作用力及利用晶体各向异性等材料设计与合成策略来实现类石墨烯的化学合成,并展望了类石墨烯的组装结构在能量存储与智能传感领域的应用前景.

  10. Topological phase transition of decoupling quasi-two-dimensional vortex pairs in La1- y Sm y MnO3 + δ ( y = 0.85, 1.0)

    Science.gov (United States)

    Bukhanko, F. N.; Bukhanko, A. F.

    2016-10-01

    Characteristic signs of the universal Nelson-Kosterlitz jump of the superconducting liquid density in the temperature dependences of the magnetization of La1- y Sm y MnO3 + δ samples with samarium concentrations y = 0.85 and 1.0, which are measured in magnetic fields 100 Oe ≤ H ≤ 3.5 kOe, are detected. As the temperature increases, the sample with y = 0.85 exhibits a crescent-shaped singularity in the dc magnetization curve near the critical temperature of decoupling vortex-antivortex pairs ( T KT ≡ T c ≈ 43 K), which is independent of measuring magnetic field H and is characteristic of the dissociation of 2D vortex pairs. A similar singularity is also detected in the sample with a samarium concentration y = 1.0 at a significantly lower temperature ( T KT ≈ 12 K). The obtained experimental results are explained in terms of the topological Kosterlitz-Thouless phase transition of dissociation of 2D vortex pairs in a quasi-two-dimensional weak Josephson coupling network.

  11. Electron and electron-phonon effects in quasi-two-dimensional molecular conductor theta-(BETS) sub 4 HgBr sub 4 (C sub 6 H sub 5 Cl): optical investigations at 300-15 K

    CERN Document Server

    Vlasova, R M; Petrov, B V; Semkin, N D; Zhilyaeva, E I; Bogdanova, O A; Lyubovskaya, R N; Graja, A

    2002-01-01

    One studied the polarized spectra of reflection and spectra of optical transmission of theta-(BETS) sub 4 HgBr sub 4 (C sub 6 H sub 5 Cl) quasi-two-dimensional molecular conductor within 700-6500 cm sup - sup 1 range under 300-15 K temperatures and within 9000-40000 cm sup - sup 1 under 300 K for two principal directions within crystal plane parallel to conducting layers of BETS molecules. Under 300 K within IR region the spectra are characterized by the intensive essential peculiarities (1200-1400 cm sup - sup 1) caused by electron-oscillation coupling (EOC). At temperature drop within 180-80 K range one observes in the spectra a Lorentz term with omega sub t = 2900 cm sup - sup 1 and three extra bands within 800-1180 cm sup - sup 1 region caused by EOC. The derived results are indicative of unstable structural distortions along two principal directions in a crystal followed by formation of a charge density comparable wave

  12. Commensurate and incommensurate states of a spin density wave in a quasi-two-dimensional system with an anisotropic energy spectrum in an external magnetic field of arbitrary direction relative to magnetization

    Energy Technology Data Exchange (ETDEWEB)

    Palistrant, M. E., E-mail: mepalistrant@yandex.com; Ursu, V. A. [Academy of Sciences of Moldova, Institute of Applied Physics (Moldova, Republic of)

    2013-04-15

    A theory of thermodynamic properties of a spin density wave (SDW) in a quasi-two-dimensional system (with a preset impurity concentration x) is constructed. We choose an anisotropic dispersion relation for the electron energy and assume that external magnetic field H has an arbitrary direction relative to magnetic moment M{sub Q}. The system of equations defining order parameters M{sub Q}{sup z}, M{sub Q}{sup {sigma}}, M{sub z}, and M{sup {sigma}} is constructed and transformed with allowance for the Umklapp processes. Special cases when H Double-Vertical-Line M{sub Q} and H Up-Tack M{sub Q} (H{sub Z}H{sup {sigma}} = 0) are considered in detail as well as cases of weak fields H of arbitrary direction. The condition for the transition of the system to the commensurate and incommensurate states of the SDW is analyzed. The concentration dependence of magnetic transition temperature T{sub M} is calculated, and the components of the order parameter for the incommensurate phase are determined. The phase diagram (T,{approx}x) is constructed. The effect of the magnetic field on magnetic transition temperature T{sub M} is analyzed for H{sub Z}H{sup {sigma}} = 0, and longitudinal magnetic susceptibility {chi} Double-Vertical-Line is calculated; this quantity demonstrates the temperature dependence corresponding to a system with a gap for x < x{sub c} and to a gapless state for x > x{sub c}. In the immediate vicinity of the critical impurity concentration (x {approx} x{sub c}), the temperature dependence of the magnetic susceptibility acquires a local maximum. The effect of anisotropy of the electron energy spectrum on the investigated physical quantities is also analyzed.

  13. Quasi-two-dimensional electron gas at the interface of γ-Al{sub 2}O{sub 3}/SrTiO{sub 3} heterostructures grown by atomic layer deposition

    Energy Technology Data Exchange (ETDEWEB)

    Ngo, Thong Q.; McDaniel, Martin D.; Ekerdt, John G., E-mail: ekerdt@che.utexas.edu [Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712 (United States); Goble, Nicholas J.; Gao, Xuan P. A. [Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106 (United States); Posadas, Agham; Kormondy, Kristy J.; Demkov, Alexander A. [Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States); Lu, Sirong [School of Engineering for Matter, Transport and Engineering, Arizona State University, Tempe, Arizona 85287 (United States); Jordan-Sweet, Jean [IBM T.J. Watson Research Center, Yorktown Heights, New York 10598 (United States); Smith, David J. [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States)

    2015-09-21

    We report the formation of a quasi-two-dimensional electron gas (2-DEG) at the interface of γ-Al{sub 2}O{sub 3}/TiO{sub 2}-terminated SrTiO{sub 3} (STO) grown by atomic layer deposition (ALD). The ALD growth of Al{sub 2}O{sub 3} on STO(001) single crystal substrates was performed at temperatures in the range of 200–345 °C. Trimethylaluminum and water were used as co-reactants. In situ reflection high energy electron diffraction, ex situ x-ray diffraction, and ex situ cross-sectional transmission electron microscopy were used to determine the crystallinity of the Al{sub 2}O{sub 3} films. As-deposited Al{sub 2}O{sub 3} films grown above 300 °C were crystalline with the γ-Al{sub 2}O{sub 3} phase. In situ x-ray photoelectron spectroscopy was used to characterize the Al{sub 2}O{sub 3}/STO interface, indicating that a Ti{sup 3+} feature in the Ti 2p spectrum of STO was formed after 2–3 ALD cycles of Al{sub 2}O{sub 3} at 345 °C and even after the exposure to trimethylaluminum alone at 300 and 345 °C. The interface quasi-2-DEG is metallic and exhibits mobility values of ∼4 and 3000 cm{sup 2} V{sup −1} s{sup −1} at room temperature and 15 K, respectively. The interfacial conductivity depended on the thickness of the Al{sub 2}O{sub 3} layer. The Ti{sup 3+} signal originated from the near-interfacial region and vanished after annealing in an oxygen environment.

  14. The use of experimental data in constraining the tight-binding band parameters of quasi-two-dimensional organic molecular metals: application to α-(BEDT- TTF)2KHg(SCN)4

    Science.gov (United States)

    Harrison, N.; Rzepniewski, E.; Singleton, J.; Gee, P. J.; Honold, M. M.; Day, P.; Kurmoo, M.

    1999-09-01

    Whilst tight-binding bandstructure calculations are very successful in describing the Fermi-surface configuration in many quasi-two-dimensional organic molecular metals, the detailed topology of the predicted Fermi surface often differs from that measured in experiments. This is very significant when, for example, the formation of a density-wave state depends critically on details of the nesting of Fermi-surface sheets. These differences between theory and experiment probably result from the limited accuracy to which the icons/Journals/Common/pi" ALT="pi" ALIGN="TOP"/>-orbitals of the component molecules (which give rise to the transfer integrals of the tight-binding bandstructure) are known. In order to surmount this problem, we have derived a method whereby the transfer integrals within a tight-binding bandstructure model are adjusted until the detailed Fermi-surface topology is in good agreement with a wide variety of experimental data. The method is applied to the charge-transfer salt icons/Journals/Common/alpha" ALT="alpha" ALIGN="TOP"/>-(BEDT-TTF)2KHg(SCN)4, the Fermi surface of which has been the source of much speculation in recent years. The Fermi surface obtained differs in detail from previous bandstructure calculation findings. In particular, the quasi-one-dimensional component of the Fermi surface is more strongly warped. This implies that upon nesting of these sheets, significant parts of the quasi-one-dimensional sheets remain, leading to a complicated Fermi-surface topology within the low-temperature, low-magnetic-field phase. In contrast to previous models of this phase, the model for the reconstructed Fermi surface in this work can explain virtually all of the current experimental observations in a consistent manner.

  15. Antiferromagnetic spintronics.

    Science.gov (United States)

    Jungwirth, T; Marti, X; Wadley, P; Wunderlich, J

    2016-03-01

    Antiferromagnetic materials are internally magnetic, but the direction of their ordered microscopic moments alternates between individual atomic sites. The resulting zero net magnetic moment makes magnetism in antiferromagnets externally invisible. This implies that information stored in antiferromagnetic moments would be invisible to common magnetic probes, insensitive to disturbing magnetic fields, and the antiferromagnetic element would not magnetically affect its neighbours, regardless of how densely the elements are arranged in the device. The intrinsic high frequencies of antiferromagnetic dynamics represent another property that makes antiferromagnets distinct from ferromagnets. Among the outstanding questions is how to manipulate and detect the magnetic state of an antiferromagnet efficiently. In this Review we focus on recent works that have addressed this question. The field of antiferromagnetic spintronics can also be viewed from the general perspectives of spin transport, magnetic textures and dynamics, and materials research. We briefly mention this broader context, together with an outlook of future research and applications of antiferromagnetic spintronics.

  16. Néel temperature of quasi-low-dimensional Heisenberg antiferromagnets.

    Science.gov (United States)

    Yasuda, C; Todo, S; Hukushima, K; Alet, F; Keller, M; Troyer, M; Takayama, H

    2005-06-03

    The Néel temperature T(N) of quasi-one- and quasi-two-dimensional antiferromagnetic Heisenberg models on a cubic lattice is calculated by Monte Carlo simulations as a function of interchain (interlayer) to intrachain (intralayer) coupling J(')/J down to J(')/J approximately = 10(-3). We find that T(N) obeys a modified random-phase approximationlike relation for small J(')/J with an effective universal renormalized coordination number, independent of the size of the spin. Empirical formulas describing T(N) for a wide range of J(') and useful for the analysis of experimental measurements are presented.

  17. Nematic ordering dynamics of an antiferromagnetic spin-1 condensate

    Science.gov (United States)

    Symes, L. M.; Blakie, P. B.

    2017-07-01

    We consider the formation of order in a quasi-two-dimensional antiferromagnetic spin-1 condensate quenched from an easy-axis to an easy-plane nematic phase. We define the relevant order parameter to quantify the spin-nematic degrees of freedom and study the evolution of the spin-nematic and superfluid order during the coarsening dynamics using numerical simulations. We observe dynamical scaling in the late-time dynamics, with both types of order extending across the system with a diffusive growth law. We identify half-quantum vortices as the relevant topological defects of the ordering dynamics and demonstrate that the growth of both types of order is determined by the mutual annihilation of these vortices.

  18. Novel charge density wave transition in crystals of R5Ir4Si10

    Indian Academy of Sciences (India)

    S Ramakrishnan

    2002-05-01

    We review the observation of novel charge density wave (CDW) transitions in ternary R5Ir4Si10 compounds. A high quality single crystal of Lu5Ir4Si10 shows the formation of a commensurate CDW along -axis below 80 K in the (ℎ, 0, ) plane that coexists with BCS type superconductivity below 3.9 K. However, in a single crystal of Er5Ir4Si10, one observes the development of a 1D-incommensurate CDW at 155 K, which then locks into a purely commensurate state below 55 K. The well-localized Er3 moments are antiferromagnetically ordered below 2.8 K which results in the coexistence of strongly coupled CDW with local moment antiferromagnetism in Er5Ir4Si10. Unlike conventional CDW systems, extremely sharp transition (width ∼ 1.5 K) in all bulk properties along with huge heat capacity anomalies in these compounds makes this CDW transition an interesting one.

  19. Fractional excitations in the square-lattice quantum antiferromagnet

    Science.gov (United States)

    Dalla Piazza, B.; Mourigal, M.; Christensen, N. B.; Nilsen, G. J.; Tregenna-Piggott, P.; Perring, T. G.; Enderle, M.; McMorrow, D. F.; Ivanov, D. A.; Rønnow, H. M.

    2015-01-01

    Quantum magnets have occupied the fertile ground between many-body theory and low-temperature experiments on real materials since the early days of quantum mechanics. However, our understanding of even deceptively simple systems of interacting spin-1/2 particles is far from complete. The quantum square-lattice Heisenberg antiferromagnet, for example, exhibits a striking anomaly of hitherto unknown origin in its magnetic excitation spectrum. This quantum effect manifests itself for excitations propagating with the specific wavevector (π, 0). We use polarized neutron spectroscopy to fully characterize the magnetic fluctuations in the metal-organic compound Cu(DCOO)2.4D2O, a known realization of the quantum square-lattice Heisenberg antiferromagnet model. Our experiments reveal an isotropic excitation continuum at the anomaly, which we analyse theoretically using Gutzwiller-projected trial wavefunctions. The excitation continuum is accounted for by the existence of spatially extended pairs of fractional S = 1/2 quasiparticles, 2D analogues of 1D spinons. Away from the anomalous wavevector, these fractional excitations are bound and form conventional magnons. Our results establish the existence of fractional quasiparticles in the high-energy spectrum of a quasi-two-dimensional antiferromagnet, even in the absence of frustration.

  20. Mechanically driven growth of quasi-two dimensional microbial colonies

    CERN Document Server

    Farrell, F D C; Marenduzzo, D; Waclaw, B

    2013-01-01

    We study colonies of non-motile, rod-shaped bacteria growing on solid substrates. In our model, bacteria interact purely mechanically, by pushing each other away as they grow, and consume a diffusing nutrient. We show that mechanical interactions control the velocity and shape of the advancing front, which leads to features that cannot be captured by established Fisher-Kolmogorov models. In particular, we find that the velocity depends on the elastic modulus of bacteria or their stickiness to the surface. Interestingly, we predict that the radius of an incompressible, strictly two-dimensional colony cannot grow linearly in time. Importantly, mechanical interactions can also account for the nonequilibrium transition between circular and branching colonies, often observed in the lab.

  1. Quasi two-dimensional astigmatic solitons in soft chiral metastructures

    Science.gov (United States)

    Laudyn, Urszula A.; Jung, Paweł S.; Karpierz, Mirosław A.; Assanto, Gaetano

    2016-03-01

    We investigate a non-homogeneous layered structure encompassing dual spatial dispersion: continuous diffraction in one transverse dimension and discrete diffraction in the orthogonal one. Such dual diffraction can be balanced out by one and the same nonlinear response, giving rise to light self-confinement into astigmatic spatial solitons: self-focusing can compensate for the spreading of a bell-shaped beam, leading to quasi-2D solitary wavepackets which result from 1D transverse self-localization combined with a discrete soliton. We demonstrate such intensity-dependent beam trapping in chiral soft matter, exhibiting one-dimensional discrete diffraction along the helical axis and one-dimensional continuous diffraction in the orthogonal plane. In nematic liquid crystals with suitable birefringence and chiral arrangement, the reorientational nonlinearity is shown to support bell-shaped solitary waves with simple astigmatism dependent on the medium birefringence as well as on the dual diffraction of the input wavepacket. The observations are in agreement with a nonlinear nonlocal model for the all-optical response.

  2. Blast shocks in quasi-two-dimensional supersonic granular flows.

    Science.gov (United States)

    Boudet, J F; Cassagne, J; Kellay, H

    2009-11-27

    In a thin, dilute, and fast flowing granular layer, the impact of a small sphere generates a fast growing hole devoid of matter. The growth of this hole is studied in detail, and its dynamics is found to mimic that of blast shocks in gases. This dynamics can be decomposed into two stages: a fast initial stage (the blast) and a slower growth regime whose growth velocity is given by the speed of sound in the medium used. A simple model using ingredients already invoked for the case of blast shocks in gases but including the inelastic nature of collisions between grains accounts accurately for our results. The system studied here allows for a detailed study of the full dynamics of a blast as it relaxes from a strong to a weak shock and later to an acoustic disturbance.

  3. Drift modes of a quasi-two-dimensional current sheet

    Energy Technology Data Exchange (ETDEWEB)

    Artemyev, A. V.; Malova, Kh. V.; Popov, V. Yu.; Zelenyi, L. M. [Russian Academy of Sciences, Space Research Institute (Russian Federation)

    2012-03-15

    Stability of a plasma configuration consisting of a thin one-dimensional current sheet embedded into a two-dimensional background current sheet is studied. Drift modes developing in plasma as unstable waves along the current direction are considered. Dispersion relations for kink and sausage perturbation modes are obtained depending on the ratio of parameters of thin and background current sheets. It is shown that the existence of the background sheet results in a decrease in the instability growth rates and a significant increase in the perturbation wavelengths. The role of drift modes in the excitation of oscillations observed in the current sheet of the Earth's magnetotail is discussed.

  4. Spin-polarized valley Hall effect in ultrathin silicon nanomembrane via interlayer antiferromagnetic coupling

    Science.gov (United States)

    Sun, Jia-Tao; Wang, Zhengfei; Meng, S.; Du, Shixuan; Liu, F.; Gao, H.-J.

    2016-09-01

    Fundamental understanding of two-dimensional materials has spurred a surge in the search for topological quantum phase associated with the valley degree of freedom (VDOF). We discuss a spin-polarized version to the VDOF in which spin degeneracy is broken by the antiferromagnetic exchange coupling (LAFM) between opposite layers of the quasi-two-dimensional silicon nanomembrane (SiNM). Based on first principles calculations, we found that the LAFM state in SiNM can lead to metal-insulator transition (MIT). The broken degeneracy of spin degree of freedom in this insulating state of ultrathin SiNM may differ for different valleys, so that the SiNM can be exploited to produce the spatially separated spin and valley currents. We propose that the tunable spin-polarized valley photocurrents can be generated in an experimentally feasible ellipsometry setup. Our work shows promise for the development of spintronic and valleytronic devices compatible with current silicon industry.

  5. Charge Transport in Antiferromagnetic Insulating Phase of Two-Dimensional Organic Conductor λ-(BETS)2FeCl4

    Science.gov (United States)

    Sugiura, Shiori; Shimada, Kazuo; Tajima, Naoya; Nishio, Yutaka; Terashima, Taichi; Isono, Takayuki; Kobayashi, Akiko; Zhou, Biao; Kato, Reizo; Uji, Shinya

    2016-06-01

    Resistance and dielectric constants have been measured in the antiferromagnetic insulating phase of the quasi-two-dimensional organic conductor λ-(BETS)2FeCl4 to understand charge transport. Nonlinear current-voltage characteristics are observed at low temperatures, which are explained by a charge transport model based on the electric-field dependent Coulomb potential between the thermally excited electron and hole. A small dip in the magnetic field dependence of the resistance is found at 1.2 T, which is ascribed to a spin-flop transition. The large difference between the in-plane and out-of-plane dielectric constants shows the two-dimensionality of the Coulomb potential, which is consistent with the charge transport model. The angular dependence of the metal-insulator transition field is determined, which suggests that the Zeeman effect of the 3d spins of the Fe ions plays an essential role.

  6. Spin frustration and magnetic ordering in triangular lattice antiferromagnet Ca3CoNb2O9

    Science.gov (United States)

    Dai, Jia; Zhou, Ping; Wang, Peng-Shuai; Pang, Fei; Munsie, Tim J.; Luke, Graeme M.; Zhang, Jin-Shan; Yu, Wei-Qiang

    2015-12-01

    We synthesized a quasi-two-dimensional distorted triangular lattice antiferromagnet Ca3CoNb2O9, in which the effective spin of Co2+ is 1/2 at low temperatures, whose magnetic properties were studied by dc susceptibility and magnetization techniques. The x-ray diffraction confirms the quality of our powder samples. The large Weiss constant θCW˜ -55 K and the low Neel temperature TN˜ 1.45 K give a frustration factor f = | θCW/TN | ≈ 38, suggesting that Ca3CoNb2O9 resides in strong frustration regime. Slightly below TN, deviation between the susceptibility data under zero-field cooling (ZFC) and field cooling (FC) is observed. A new magnetic state with 1/3 of the saturate magnetization Ms is suggested in the magnetization curve at 0.46 K. Our study indicates that Ca3CoNb2O9 is an interesting material to investigate magnetism in triangular lattice antiferromagnets with weak anisotropy. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374364 and 11222433), the National Basic Research Program of China (Grant No. 2011CBA00112). Research at McMaster University supported by the Natural Sciences and Engineering Research Council. Work at North China Electric Power University supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry.

  7. Ground state configurations in antiferromagnetic ultrathin films with dipolar anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Leon, H., E-mail: hleon@imre.oc.uh.cu [Instituto de Ciencia y Tecnologia de Materiales, Universidad de La Habana, Zapata e/ Mazon y G. Vedado, 10400 La Habana (Cuba)

    2013-02-15

    The formalism developed in a previous work to calculate the dipolar energy in quasi-two-dimensional crystals with ferromagnetic order is now extended to collinear antiferromagnetic order. Numerical calculations of the dipolar energy are carried out for systems with tetragonally distorted fcc [001] structures, the case of NiO and MnO ultrathin film grown in non-magnetic substrates, where the magnetic phase is a consequence of superexchange and dipolar interactions. The employed approximation allows to demonstrate that dipolar coupling between atomic layers is responsible for the orientation of the magnetization when it differs from the one in a single layer. The ground state energy of a given NiO or MnO film is found to depend not only on the strain, but also on how much the interlayer separation and the 2D lattice constant are changed with respect to the ideal values corresponding to the non-distorted cubic structure. Nevertheless, it is shown that the orientation of the magnetization in the magnetic phase of any of these films is determined by the strain exclusively. A striped phase with the magnetization along the [112{sup Macron }] direction appears as the ground state configuration of NiO and MnO ultrathin films. In films with equally oriented stripes along the layers this magnetic phase is twofold degenerate, while in films with multidomain layers it is eightfold degenerate. These results are not in contradiction with experimentally observed out-of-plane or in-plane magnetization of striped phases in NiO and MnO ultrathin films. - Highlights: Black-Right-Pointing-Pointer Dipolar energy in collinear antiferromagnetic ultrathin films is calculated. Black-Right-Pointing-Pointer Numerical results are presented for distorted fcc [001] structures. Black-Right-Pointing-Pointer The lowest energy of a system depends on how the tetragonal distortion is achieved. Black-Right-Pointing-Pointer A striped phase with magnetization in the [112{sup Macron }] direction is the

  8. Quantum-critical fluctuations in 2D metals: strange metals and superconductivity in antiferromagnets and in cuprates

    Science.gov (United States)

    Varma, Chandra M.

    2016-08-01

    The anomalous transport and thermodynamic properties in the quantum-critical region, in the cuprates, and in the quasi-two dimensional Fe-based superconductors and heavy-fermion compounds, have the same temperature dependences. This can occur only if, despite their vast microscopic differences, a common statistical mechanical model describes their phase transitions. The antiferromagnetic (AFM)-ic models for the latter two, just as the loop-current model for the cuprates, map to the dissipative XY model. The solution of this model in (2+1)D reveals that the critical fluctuations are determined by topological excitations, vortices and a variety of instantons, and not by renormalized spin-wave theories of the Landau-Ginzburg-Wilson type, adapted by Moriya, Hertz and others for quantum-criticality. The absorptive part of the fluctuations is a separable function of momentum \\mathbf{q} , measured from the ordering vector, and of the frequency ω and the temperature T which scale as \\tanh (ω /2T) at criticality. Direct measurements of the fluctuations by neutron scattering in the quasi-two-dimensional heavy fermion and Fe-based compounds, near their antiferromagnetic quantum critical point, are consistent with this form. Such fluctuations, together with the vertex coupling them to fermions, lead to a marginal fermi-liquid, with the imaginary part of the self-energy \\propto \\text{max}(ω,T) for all momenta, a resistivity \\propto T , a T\\ln T contribution to the specific heat, and other singular fermi-liquid properties common to these diverse compounds, as well as to d-wave superconductivity. This is explicitly verified, in the cuprates, by analysis of the pairing and the normal self-energy directly extracted from the recent high resolution angle resolved photoemission measurements. This reveals, in agreement with the theory, that the frequency dependence of the attractive irreducible particle-particle vertex in the d-wave channel is the same as the irreducible

  9. Antiferromagnetic spin-orbitronics

    KAUST Repository

    Manchon, Aurelien

    2015-05-01

    Antiferromagnets have long remained an intriguing and exotic state of matter, whose application has been restricted to enabling interfacial exchange bias in metallic and tunneling spin-valves [1]. Their role in the expanding field of applied spintronics has been mostly passive and the in-depth investigation of their basic properties mostly considered from a fundamental perspective.

  10. Nanoparticles of antiferromagnetic materials

    DEFF Research Database (Denmark)

    Madsen, Daniel Esmarch

    2008-01-01

    I denne Ph.D. afhandling studeres forskellige egenskaber ved antiferromagnetiske nanopartikler. I en ideel antiferromagnet er spinnene orienteret således at der ikke er et resulterende magnetisk moment. I nanopartikler af antiferromagnetiske materialer er denne kompensation på grund af forskellig...

  11. Thermodynamic investigations of the quasi-2d triangular Heisenberg antiferromagnet Cs{sub 2}CuCl{sub 2}Br{sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Tutsch, Ulrich; Postulka, Lars; Wolf, Bernd; Lang, Michael; Well, Natalija van; Ritter, Franz; Krellner, Cornelius; Assmus, Wolf [Physikalisches Institut, Goethe-University Frankfurt (Germany)

    2015-07-01

    The system Cs{sub 2}CuCl{sub 4-x}Br{sub x} (0 ≤ x ≤ 4) is a quasi-two-dimensional Heisenberg antiferromagnet with a triangular in-plane arrangement of the spin-spin couplings. The ratio J{sup '}/J of the corresponding coupling constants determines the degree of frustration in the system and has been found to be 0.34 (x = 0) and 0.74 (x = 4) for the border compounds. One may ask whether for some intermediate Br concentration an even higher degree of frustration can be reached. Indeed, some indications have been reported by Ono et al. Here, we present specific heat C and susceptibility χ measurements below 1 K in magnetic fields B up to 13.5 T for the intermediate compound Cs{sub 2}CuCl{sub 2}Br{sub 2}, which, due to site-selective substitution, shows a well-ordered halide sublattice. Indications for an antiferromagnetic transition are observed around 90 mK for B = 0. A small field of B = 0.14 T is sufficient to fully suppress this anomaly. Taking into account the high saturation field of about 20 T, extrapolated from χ(T = const, B) scans at low temperatures, this small ordered region in the B-T plane clearly indicates a high degree of frustration in Cs{sub 2}CuCl{sub 2}Br{sub 2}.

  12. A theoretical study of the extinction of antiferromagnetic order by holes and dilution in LaSrCuZnO

    Science.gov (United States)

    Ricardo de Sousa, J.; Pacobahyba, J. T. M.; Singh, M.

    2009-01-01

    We have used the quasi-two-dimensional Heisenberg antiferromagnetic model to explain the extinction of long-range order by holes and dilution in LaSrCuZnO. An analytical expression is obtained for the Néel temperature TN(x,z) by using the Green's-function formalism with random phase approximation (RPA). The expression for the Néel temperature TN(x,z) is a function of concentration of holes x and dilution z. To treat the dilution effect in CuO 2 plane (XY), we use three different approximations for percolation. The frustration effect is induced by interplane coupling which depends linearly on the doping concentration x. We have explained qualitatively the non-monotonic and reentrant behavior of TN(x,z) which was observed experimentally by Hücker [M. Hücker, V. Kataev, J. Pommer, J. Harass, A. Hosni, C. Pflitsch, R. Gross, B. Buchner, Phys. Rev. B 59 (1999) R725].

  13. Collinear antiferromagnetism in trigonal SrMn2As2 revealed by single-crystal neutron diffraction

    Science.gov (United States)

    Das, Pinaki; Sangeetha, N. S.; Pandey, Abhishek; Benson, Zackery A.; Heitmann, T. W.; Johnston, D. C.; Goldman, A. I.; Kreyssig, A.

    2017-01-01

    Iron pnictides and related materials have been a topic of intense research for understanding the complex interplay between magnetism and superconductivity. Here we report on the magnetic structure of SrMn2As2 that crystallizes in a trigonal structure (P\\bar{3}m1 ) and undergoes an antiferromagnetic (AFM) transition at {{T}\\text{N}}=118(2) K. The magnetic susceptibility remains nearly constant at temperatures T≤slant {{T}\\text{N}} with \\boldsymbol{H}\\parallel \\boldsymbol{c} whereas it decreases significantly with \\boldsymbol{H}\\parallel \\boldsymbol{a}\\boldsymbol{b} . This shows that the ordered Mn moments lie in the \\boldsymbol{a}\\boldsymbol{b} plane instead of aligning along the \\boldsymbol{c} -axis as in tetragonal BaMn2As2. Single-crystal neutron diffraction measurements on SrMn2As2 demonstrate that the Mn moments are ordered in a collinear Néel AFM phase with {{180}\\circ} AFM alignment between a moment and all nearest neighbor moments in the basal plane and also perpendicular to it. Moreover, quasi-two-dimensional AFM order is manifested in SrMn2As2 as evident from the temperature dependence of the order parameter.

  14. Holes in Heisenberg antiferromagnets

    Science.gov (United States)

    Chen, Yang

    1990-05-01

    In this Brief Report we show that a recent model proposed by Shankar [Phys. Rev. Lett. 63, 203 (1989)], describing the motion of holes in quantum antiferromagnets is equivalent to the Schwinger model [Phys. Rev. 128, 2425 (1962)] in 1+1 dimensions. Some exact results are deduced. In addition to the superconducting long-range order found by Shankar, it is shown that there is a 2pF hole density wave existing with the superconducting pairing instability.

  15. Antiferromagnetic hedgehogs with superconducting cores

    Energy Technology Data Exchange (ETDEWEB)

    Goldbart, P.M.; Sheehy, D.E. [Department of Physics and Materials Research Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (United States)

    1998-09-01

    Excitations of the antiferromagnetic state that resemble antiferromagnetic hedgehogs at large distances but are predominantly superconducting inside a core region are discussed within the context of Zhang{close_quote}s SO(5)-symmetry-based approach to the physics of high-temperature superconducting materials. Nonsingular, in contrast with their hedgehog cousins in pure antiferromagnetism, these texture excitations are what hedgehogs become when the antiferromagnetic order parameter is permitted to {open_quotes}escape{close_quotes} into superconducting directions. The structure of such excitations is determined in a simple setting, and a number of their experimental implications are examined. {copyright} {ital 1998} {ital The American Physical Society}

  16. Direct observation of strong localization of quasi-two-dimensional light waves

    DEFF Research Database (Denmark)

    Bozhevolnyi, Sergey I.

    1999-01-01

    Scattering of surface plasmon polaritons on rough metal surfaces is investigated by using scanning near-field optical microscopy. Different scattering regimes, i.e. single, double and multiple scattering, are observed and related to the spatial Fourier spectra of the corresponding near......-field optical images. For the regime of strong multiple scattering, the near-field optical images exhibit spatially localized (within 150-250 nm) intensity enhancement by 10-50 times. This feature is attributed to strong localization of surface polaritons due to interference effects in multiple scattering...... caused by surface roughness. Similar bright light spots are observed with light scattering by silver colloid clusters deposited on glass substrates. Differences and similarities in these scattering phenomena are discussed....

  17. Uncertainty analysis of quasi-two-dimensional flow simulation in compound channels with overbank flows

    OpenAIRE

    Riahi-Madvar, Hossien; Ayyoubzadeh, Seyed Ali; Namin, Masoud Montazeri; Seifi, Akram

    2011-01-01

    Flow in compound channels with overbank flows becomes more complex because of shear interactions between flows in main channel and flood plains, lateral momentum transfer and secondary flows. Compound channels have interesting applications in flood control, civil engineering and environmental management. Because it is difficult to obtain sufficiently accurate and comprehensive understandings of flow in natural compound rivers, the developed models of flow in overbank flows have many uncertain...

  18. Experimentally determining the exchange parameters of quasi-two dimensional Heisenbert magnets

    Energy Technology Data Exchange (ETDEWEB)

    Singleton, John [Los Alamos National Laboratory; Sengupta, P [Los Alamos National Laboratory; Mcdonald, R D [Los Alamos National Laboratory; Cox, S [Los Alamos National Laboratory; Harrison, N [Los Alamos National Laboratory; Goddard, P A [UNIV OF OXFORD; Lancaster, T [UNIV OF OXFORD; Blundell, S J [UNIV OF OXFORD; Pratt, F L [RUTHERFORD APPLETON LAB; Manson, J L [EASTERN WASHINGTON UNIV; Southerland, H I [EASTERN WASHINGTON UNIV; Schlueter, J A [ANL

    2008-01-01

    Though long-range magnetic order cannot occur at temperatures T > 0 in a perfect two-dimensional (2D) Heisenberg magnet, real quasi-2D materials will invariably possess nonzero inter-plane coupling J{sub {perpendicular}} driving the system to order at elevated temperatures. This process can be studied using quantum Monte Carlo calculations. However, it is difficult to test the results of these calculations experimentally since for highly anisotropic materials in which the in-plane coupling is comparable with attainable magnetic fields J{sub {perpendicular}} is necessarily very small and inaccessible directly. In addition, because of the large anisotropy, the Neel temperatures are low and difficult to determine from thermodynamic measurements. Here, we present an elegant method of assessing the calculations via two independent experimental probes: pulsed-field magnetization in fields of up to 85 T, and muon-spin rotation.

  19. Interactions of a Quasi-Two-Dimensional Vortex with a Stationary and Oscillating Leading-Edge

    Science.gov (United States)

    1996-07-01

    together. I also thank mi hermano Fernando and the members of Hamilton Branch and Kutztown Ward for the fun times we’ve shared that have helped to...19 v K 1.8.2 Summary of Research Objectives .................................................. 20 1.9 Outline of...absence of a uniform flow the vortex will convect to the left with self-induced speed Vs=ic/2a, where K is the vortex strength (F = 2itic) and a is the

  20. Observations of the sedimentation of individual particles in a quasi-two dimensional system

    Science.gov (United States)

    Ramos, Eduardo; Lee, Andrew; Goldman, Daniel; Swinney, Harry

    2002-11-01

    We report observations of single sedimenting acrylic spheres (diameter = 3.175 mm, relative density = 1.19) in a vertical Hele-Shaw cell formed by two parallel glass plates and filled with water. The distance between walls of the cell varies from 1.1 to 1.3 sphere diameters; the corresponding sedimenting Reynolds number varies from 220 to 300. In the narrower cell, a wake was formed by an attached vortical region behind the sphere with two asymetrical branches. These branches oscillated and shed vortices alternately; this structure is similar to the Von Karman vortex street generated by a fixed cylinder exposed to a constant flow at approximately the same Reynolds number. In contrast, the wake of a sphere falling in a cell with a gap of 1.3 diameters was similar to that for a sphere in an infinite system at Reynolds numbers slightly larger than the threshhold for the onset of periodic wake oscillations (Re 300): the sphere sheds vortex loops, which are separated by counterotating pairs of vortex filaments.

  1. Dephasing in the quasi-two-dimensional exciton-biexciton system

    DEFF Research Database (Denmark)

    Langbein, Wolfgang Werner; Hvam, Jørn Märcher

    2000-01-01

    The polarization decay in the exciton-biexciton system of a homogeneously broadened single quantum well is studied by transient four-wave mixing. All three decay rates in the exciton-biexciton three-level system are deduced. The relation between the rates unravels correlations between scattering...... processes of excitons and biexcitons. Density and temperature dependences show that the involved processes are mainly radiative decay and phonon scattering. The radiative decay rate of the biexcitons is found to be comparable to the one of the excitons, and the involved spontaneous photon emissions from...

  2. Motility of \\textit{Escherichia coli} in a quasi-two-dimensional porous medium

    CERN Document Server

    Sosa-Hernández, Juan Eduardo; Santana-Solano, Jesús

    2016-01-01

    Bacterial migration through confined spaces is critical for several phenomena like: biofilm formation, bacterial transport in soils, and bacterial therapy against cancer . In the present work, \\textit{E. coli} (strain K12-MG1655 WT) motility was characterized by recording and analyzing individual bacterium trajectories in a simulated quasi-2-dimensional porous medium. The porous medium was simulated by enclosing, between slide and cover slip, a bacterial-culture sample mixed with uniform 2.98 $\\mu m$ spherical latex particles. The porosity of the medium was controlled by changing the latex particle concentration. By statistically analyzing trajectory parameters like: instantaneous velocity and turn angle, as well as mean squared displacement, we were able to quantify the effects that different latex particle concentrations have upon bacterial motility. To better understand our results, bacterial trajectories were simulated by means of a phenomenological random-walk model (developed ad hoc), and the simulated ...

  3. Coexistence of superconductivity and density waves in quasi-two-dimensional metals

    Energy Technology Data Exchange (ETDEWEB)

    Ismer, Jan-Peter

    2011-06-03

    This dissertation deals with the high-temperature superconductivity in the hole- and electron-doped copper superconductors. In the first part, superconducting phases are investigated on a background of different types of density waves. Singlet superconductivity is studied with s- and d-wave symmetry on a background of spin, charge or D-density waves with respect to stability as well as phase structure and impulse dependence of the gap function. In the second part, the dynamic spin susceptibility for different phases is calculated and compared with experimental data extracted from results of inelastic neutron scattering experiments. The observed phases are d-wave superconductivity, D-density wave, and coexistence of the two. For d-wave superconductivity, the influence of a magnetic field parallel to the copper oxide layer and the temperature development of the susceptibility when for T >> T{sub c} a spin density wave phase is present are investigated. [German] Diese Dissertation beschaeftigt sich mit der Hochtemperatursupraleitung in den loch- und elektron-dotierten Kuprat-Supraleitern. Im ersten Teil der Arbeit werden supraleitende Phasen auf einem Hintergrund verschiedener Typen von Dichtewellen untersucht. Es wird Singlett-Supraleitung mit s- und d-Wellen-Symmetrie auf einem Hintergrund von Spin-, Ladungs- oder D-Dichtewelle hinsichtlich Stabilitaet sowie Phasenstruktur und Impulsabhaengigkeit der Gapfunktion untersucht. Im zweiten Teil wird die dynamische Spinsuszeptibilitaet fuer verschiedene Phasen berechnet und mit experimentellen Daten verglichen, die aus Ergebnissen von Inelastischen Neutronenstreuungsexperimenten extrahiert wurden. Die betrachteten Phasen sind d-Wellen-Supraleitung, D-Dichtewelle und Koexistenz der beiden. Fuer d-Wellen-Supraleitung werden der Einfluss eines Magnetfelds parallel zur Kupferoxidschicht und die Temperaturentwicklung der Suszeptibilitaet, wenn fuer T >> T{sub c} eine Spin-Dichtewelle-Phase vorliegt, untersucht.

  4. Bubble statistics and coarsening dynamics for quasi-two-dimensional foams with increasing liquid content.

    Science.gov (United States)

    Roth, A E; Jones, C D; Durian, D J

    2013-04-01

    We report on the statistics of bubble size, topology, and shape and on their role in the coarsening dynamics for foams consisting of bubbles compressed between two parallel plates. The design of the sample cell permits control of the liquid content, through a constant pressure condition set by the height of the foam above a liquid reservoir. We find that in the scaling regime, all bubble distributions are independent not only of time, but also of liquid content. For coarsening, the average rate decreases with liquid content due to the blocking of gas diffusion by Plateau borders inflated with liquid; we achieve a factor of 4 reduction from the dry limit. By observing the growth rate of individual bubbles, we find that von Neumann's law becomes progressively violated with increasing wetness and decreasing bubble size. We successfully model this behavior by explicitly incorporating the border-blocking effect into the von Neumann argument. Two dimensionless bubble shape parameters naturally arise, one of which is primarily responsible for the violation of von Neumann's law for foams that are not perfectly dry.

  5. Final Report - Composite Fermion Approach to Strongly Interacting Quasi Two Dimensional Electron Gas Systems

    Energy Technology Data Exchange (ETDEWEB)

    Quinn, John

    2009-11-30

    Work related to this project introduced the idea of an effective monopole strength Q* that acted as the effective angular momentum of the lowest shell of composite Fermions (CF). This allowed us to predict the angular momentum of the lowest band of energy states for any value of the applied magnetic field simply by determining N{sub QP} the number of quasielectrons (QE) or quasiholes (QH) in a partially filled CF shell and adding angular momenta of the N{sub QP} Fermions excitations. The approach reported treated the filled CF level as a vacuum state which could support QE and QH excitations. Numerical diagonalization of small systems allowed us to determine the angular momenta, the energy, and the pair interaction energies of these elementary excitations. The spectra of low energy states could then be evaluated in a Fermi liquid-like picture, treating the much smaller number of quasiparticles and their interactions instead of the larger system of N electrons with Coulomb interactions.

  6. Layer-dependent anisotropic electronic structure of freestanding quasi-two-dimensional Mo S 2

    KAUST Repository

    Hong, Jinhua

    2016-02-29

    The anisotropy of the electronic transition is a well-known characteristic of low-dimensional transition-metal dichalcogenides, but their layer-thickness dependence has not been properly investigated experimentally until now. Yet, it not only determines the optical properties of these low-dimensional materials, but also holds the key in revealing the underlying character of the electronic states involved. Here we used both angle-resolved electron energy-loss spectroscopy and spectral analysis of angle-integrated spectra to study the evolution of the anisotropic electronic transition involving the low-energy valence electrons in the freestanding MoS2 layers with different thicknesses. We are able to demonstrate that the well-known direct gap at 1.8 eV is only excited by the in-plane polarized field while the out-of-plane polarized optical gap is 2.4 ± 0.2 eV in monolayer MoS2. This contrasts with the much smaller anisotropic response found for the indirect gap in the few-layer MoS2 systems. In addition, we determined that the joint density of states associated with the indirect gap transition in the multilayer systems and the corresponding indirect transition in the monolayer case has a characteristic three-dimensional-like character. We attribute this to the soft-edge behavior of the confining potential and it is an important factor when considering the dynamical screening of the electric field at the relevant excitation energies. Our result provides a logical explanation for the large sensitivity of the indirect transition to thickness variation compared with that for the direct transition, in terms of quantum confinement effect.

  7. High-field studies of quantum oscillations in quasi-two-dimensional organic metals

    Science.gov (United States)

    Sandhu, Pravindrajit

    The organic metals derived from the molecule BEDT-TTF (or ET for short) are important as model systems for the study of low-dimensional phenomena. These materials are molecular crystals with a low Fermi energy (10--100 meV), high mobility (˜104 cm2/Vs) and highly anisotropic Fermi surfaces. We have conducted experimental studies of ( i) the Shubnikov-de Haas (SdH) effect in pulsed fields up to 50 T and (ii) the de Haas-van Alphen (dHvA) effect in steady fields up to 33 T on alpha - (ET)2 MHg(SCN) 4 (where M = K, Tl and NH4) and kappa - (ET)2 Cu (NCS)2. At these high fields, the wave shape as well as the temperature and field-dependence of the oscillations deviate from the behavior predicted by the standard Lifshitz-Kosevich theory. These measurements reveal the limits of the conventional theory of metals and lay the ground-work for extending the theory to low-dimensional systems. We have also performed extended Huckel tight-binding calculations to model the effects of pressure and uniaxial stress on the electronic band structure of kappa - (ET)2 KHg (SCN)4 and kappa - (ET)2 Cu (NCS)2. The calculated changes in the Fermi surface topology are in excellent agreement with the experimental values determined from SdH measurements. We also report predictions of the effects of uniaxial stress in the transverse directions and discuss the behavior of the effective mass and magnetic breakdown probability. Finally, we have investigated the origin of anomalous magnetic breakdown frequencies in the dHvA effect that are forbidden according to semi-classical theories. We construct a tight-binding model based on the realistic band-structure of the system, which is then solved numerically to compute the field-dependence of the magnetization. This model provides a natural description for the phenomenon of magnetic breakdown between co-existing closed and open Fermi surfaces and accounts for the anomalous frequencies that are observed experimentally. The occurrence of these frequencies in the dHvA signal is found to be a quantum mechanical effect arising from differences in field dependence of the states in the two partially occupied bands near the Fermi level.

  8. Spin eigen-states of Dirac equation for quasi-two-dimensional electrons

    Energy Technology Data Exchange (ETDEWEB)

    Eremko, Alexander, E-mail: eremko@bitp.kiev.ua [Bogolyubov Institute for Theoretical Physics, Metrologichna Sttr., 14-b, Kyiv, 03680 (Ukraine); Brizhik, Larissa, E-mail: brizhik@bitp.kiev.ua [Bogolyubov Institute for Theoretical Physics, Metrologichna Sttr., 14-b, Kyiv, 03680 (Ukraine); Loktev, Vadim, E-mail: vloktev@bitp.kiev.ua [Bogolyubov Institute for Theoretical Physics, Metrologichna Sttr., 14-b, Kyiv, 03680 (Ukraine); National Technical University of Ukraine “KPI”, Peremohy av., 37, Kyiv, 03056 (Ukraine)

    2015-10-15

    Dirac equation for electrons in a potential created by quantum well is solved and the three sets of the eigen-functions are obtained. In each set the wavefunction is at the same time the eigen-function of one of the three spin operators, which do not commute with each other, but do commute with the Dirac Hamiltonian. This means that the eigen-functions of Dirac equation describe three independent spin eigen-states. The energy spectrum of electrons confined by the rectangular quantum well is calculated for each of these spin states at the values of energies relevant for solid state physics. It is shown that the standard Rashba spin splitting takes place in one of such states only. In another one, 2D electron subbands remain spin degenerate, and for the third one the spin splitting is anisotropic for different directions of 2D wave vector.

  9. Critical behavior of quasi-two-dimensional semiconducting ferromagnet Cr2Ge2Te6

    Science.gov (United States)

    Liu, Yu; Petrovic, C.

    2017-08-01

    The critical properties of the single-crystalline semiconducting ferromagnet Cr2Ge2Te6 were investigated by bulk dc magnetization around the paramagnetic to ferromagnetic phase transition. Critical exponents β =0.200 ±0.003 with a critical temperature Tc=62.65 ±0.07 K and γ =1.28 ±0.03 with Tc=62.75 ±0.06 K are obtained by the Kouvel-Fisher method whereas δ =7.96 ±0.01 is obtained by a critical isotherm analysis at Tc=62.7 K. These critical exponents obey the Widom scaling relation δ =1 +γ /β , indicating self-consistency of the obtained values. With these critical exponents the isotherm M (H ) curves below and above the critical temperatures collapse into two independent universal branches, obeying the single scaling equation m =f±(h ) , where m and h are renormalized magnetization and field, respectively. The determined exponents match well with those calculated from the results of the renormalization group approach for a two-dimensional Ising system coupled with a long-range interaction between spins decaying as J (r ) ≈r-(d +σ ) with σ =1.52 .

  10. Nanofluidic electrokinetics in quasi-two-dimensional branched U-turn channels

    NARCIS (Netherlands)

    Parikesit, G.O.F.

    2008-01-01

    Lab-on-a-Chip (LOC) is a new technology focused on analyzing and controlling flows of fluids, ions, and (bio) particles on the nanometer and micrometer scales, allowing us to shrink a complete fluid-based laboratory into a coin-sized instrumentation. In this thesis, we study a novel fluidic structur

  11. Short-time dynamics of monomers and dimers in quasi-two-dimensional colloidal mixtures

    Science.gov (United States)

    Sarmiento-Gómez, Erick; Villanueva-Valencia, José Ramón; Herrera-Velarde, Salvador; Ruiz-Santoyo, José Arturo; Santana-Solano, Jesús; Arauz-Lara, José Luis; Castañeda-Priego, Ramón

    2016-07-01

    We report on the short-time dynamics in colloidal mixtures made up of monomers and dimers highly confined between two glass plates. At low concentrations, the experimental measurements of colloidal motion agree well with the solution of the Navier-Stokes equation at low Reynolds numbers; the latter takes into account the increase in the drag force on a colloidal particle due to wall-particle hydrodynamic forces. More importantly, we find that the ratio of the short-time diffusion coefficient of the monomer and that of the center of mass of the dimmer is almost independent of both the dimer molar fraction, xd, and the total packing fraction, ϕ , up to ϕ ≈0.5 . At higher concentrations, this ratio displays a small but systematic increase. A similar physical scenario is observed for the ratio between the parallel and the perpendicular components of the short-time diffusion coefficients of the dimer. This dynamical behavior is corroborated by means of molecular dynamics computer simulations that include explicitly the particle-particle hydrodynamic forces induced by the solvent. Our results suggest that the effects of colloid-colloid hydrodynamic interactions on the short-time diffusion coefficients are almost identical and factorable in both species.

  12. Three-dimensional vortex solitons in quasi-two-dimensional lattices.

    Science.gov (United States)

    Leblond, Hervé; Malomed, Boris A; Mihalache, Dumitru

    2007-08-01

    We consider the three-dimensional (3D) Gross-Pitaevskii or nonlinear Schrödinger equation with a quasi-2D square-lattice potential (which corresponds to the optical lattice trapping a self-attractive Bose-Einstein condensate, or, in some approximation, to a photonic-crystal fiber, in terms of nonlinear optics). Stable 3D solitons, with embedded vorticity S=1 and 2, are found by means of the variational approximation and in a numerical form. They are built, basically, as sets of four fundamental solitons forming a rhombus, with phase shifts piS2 between adjacent sites, and an empty site in the middle. The results demonstrate two species of stable 3D solitons, which were not studied before, viz., localized vortices ("spinning light bullets," in terms of optics) with S>1 , and vortex solitons (with any S not equal 0 ) supported by a lattice in the 3D space. Typical scenarios of instability development (collapse or decay) of unstable localized vortices are identified too.

  13. Motility of \\textit{Escherichia coli} in a quasi-two-dimensional porous medium

    OpenAIRE

    Sosa-Hernández, Juan Eduardo; Zerón, Moisés Santillán; Santana-Solano, Jesús

    2016-01-01

    Bacterial migration through confined spaces is critical for several phenomena like: biofilm formation, bacterial transport in soils, and bacterial therapy against cancer . In the present work, \\textit{E. coli} (strain K12-MG1655 WT) motility was characterized by recording and analyzing individual bacterium trajectories in a simulated quasi-2-dimensional porous medium. The porous medium was simulated by enclosing, between slide and cover slip, a bacterial-culture sample mixed with uniform 2.98...

  14. Quasi-two-dimensional optomechanical crystals with a complete phononic bandgap

    CERN Document Server

    Alegre, Thiago P Mayer; Winger, Martin; Painter, Oskar

    2010-01-01

    A fully planar two-dimensional optomechanical crystal formed in a silicon microchip is used to create a structure devoid of phonons in the GHz frequency range. A nanoscale photonic crystal cavity is placed inside the phononic bandgap crystal in order to probe the properties of the localized acoustic modes. By studying the trends in mechanical damping, mode density, and optomechanical coupling strength of the acoustic resonances over an array of structures with varying geometric properties, clear evidence of a complete phononic bandgap is shown.

  15. Antiferromagnetic spin Seebeck effect.

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-03

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2. A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF2(110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2–80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9T) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

  16. Antiferromagnetic Spin Seebeck Effect

    Science.gov (United States)

    Wu, Stephen M.; Zhang, Wei; KC, Amit; Borisov, Pavel; Pearson, John E.; Jiang, J. Samuel; Lederman, David; Hoffmann, Axel; Bhattacharya, Anand

    2016-03-01

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF2 . A device scale on-chip heater is deposited on a bilayer of MnF2 (110) (30 nm )/Pt (4 nm) grown by molecular beam epitaxy on a MgF2 (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF2 through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop transition corresponding to the sudden rotation of antiferromagnetic spins out of the easy axis is observed in the spin Seebeck signal when large magnetic fields (>9 T ) are applied parallel to the easy axis of the MnF2 thin film. When the magnetic field is applied perpendicular to the easy axis, the spin-flop transition is absent, as expected.

  17. Electrical switching of an antiferromagnet.

    Science.gov (United States)

    Wadley, P; Howells, B; Železný, J; Andrews, C; Hills, V; Campion, R P; Novák, V; Olejník, K; Maccherozzi, F; Dhesi, S S; Martin, S Y; Wagner, T; Wunderlich, J; Freimuth, F; Mokrousov, Y; Kuneš, J; Chauhan, J S; Grzybowski, M J; Rushforth, A W; Edmonds, K W; Gallagher, B L; Jungwirth, T

    2016-02-05

    Antiferromagnets are hard to control by external magnetic fields because of the alternating directions of magnetic moments on individual atoms and the resulting zero net magnetization. However, relativistic quantum mechanics allows for generating current-induced internal fields whose sign alternates with the periodicity of the antiferromagnetic lattice. Using these fields, which couple strongly to the antiferromagnetic order, we demonstrate room-temperature electrical switching between stable configurations in antiferromagnetic CuMnAs thin-film devices by applied current with magnitudes of order 10(6) ampere per square centimeter. Electrical writing is combined in our solid-state memory with electrical readout and the stored magnetic state is insensitive to and produces no external magnetic field perturbations, which illustrates the unique merits of antiferromagnets for spintronics.

  18. Antiferromagnetic spin Seebeck Effect

    OpenAIRE

    Wu, SM; W. Zhang; Kc, A; Borisov, P.; Pearson, JE; Jiang, JS; Lederman, D.; Hoffmann, A.; Bhattacharya, A

    2015-01-01

    We report on the observation of the spin Seebeck effect in antiferromagnetic MnF_{2}. A device scale on-chip heater is deposited on a bilayer of MnF_{2} (110) (30  nm)/Pt (4 nm) grown by molecular beam epitaxy on a MgF_{2} (110) substrate. Using Pt as a spin detector layer, it is possible to measure the thermally generated spin current from MnF_{2} through the inverse spin Hall effect. The low temperature (2-80 K) and high magnetic field (up to 140 kOe) regime is explored. A clear spin-flop t...

  19. Superconductivity, antiferromagnetism, and neutron scattering

    Energy Technology Data Exchange (ETDEWEB)

    Tranquada, John M., E-mail: jtran@bnl.gov; Xu, Guangyong; Zaliznyak, Igor A.

    2014-01-15

    High-temperature superconductivity in both the copper-oxide and the iron–pnictide/chalcogenide systems occurs in close proximity to antiferromagnetically ordered states. Neutron scattering has been an essential technique for characterizing the spin correlations in the antiferromagnetic phases and for demonstrating how the spin fluctuations persist in the superconductors. While the nature of the spin correlations in the superconductors remains controversial, the neutron scattering measurements of magnetic excitations over broad ranges of energy and momentum transfers provide important constraints on the theoretical options. We present an overview of the neutron scattering work on high-temperature superconductors and discuss some of the outstanding issues. - Highlights: • High-temperature superconductivity is closely associated with antiferromagnetism. • Antiferromagnetic spin fluctuations coexist with the superconductivity. • Neutron scattering is essential for characterising the full spectrum of spin excitations.

  20. Heat capacity and magnetic phase diagram of the low-dimensional antiferromagnet Y{sub 2}BaCuO{sub 5}

    Energy Technology Data Exchange (ETDEWEB)

    Knafo, W; Meingast, C; Wolf, Th; Loehneysen, H v [Forschungszentrum Karlsruhe, Institut fuer Festkoerperphysik, D-76021 Karlsruhe (Germany); Inaba, A [Research Center for Molecular Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan)

    2008-08-20

    A study by specific heat of a polycrystalline sample of the low-dimensional magnetic system Y{sub 2}BaCuO{sub 5} is presented. Magnetic fields up to 14 T are applied and permit us to extract the (T,H) phase diagram. Below {mu}{sub 0}H* approx. = 2 T, the Neel temperature, associated with a three-dimensional antiferromagnetic long-range ordering, is constant and equals T{sub N} = 15.6 K. Above H*, T{sub N} increases linearly with H and a field-induced increase of the entropy at T{sub N} is related to the presence of an isosbestic point at T{sub X} approx. = 20 K, where all the specific-heat curves cross. A comparison is made between Y{sub 2}BaCuO{sub 5} and the quasi-two-dimensional magnetic systems BaNi{sub 2}V{sub 2}O{sub 8}, Sr{sub 2}CuO{sub 2}Cl{sub 2} and Pr{sub 2}CuO{sub 4}, for which very similar phase diagrams have been reported. An effective field-induced magnetic anisotropy is proposed to explain these phase diagrams.

  1. Effects of frustration and cyclic exchange on the spin-1/2 Heisenberg antiferromagnet within the self-consistent spin-wave theory

    Science.gov (United States)

    Rutonjski, Milica S.; Pavkov-Hrvojević, Milica V.; Berović, Maja B.

    2016-12-01

    The relevance of the quasi-two-dimensional spin-1/2 frustrated quantum antiferromagnet (AFM) due to its possibility of modeling the high-temperature superconducting parent compounds has resulted in numerous theoretical and experimental studies. This paper presents a detailed research of the influence of the varying exchange interactions on the model magnetic properties within the framework of self-consistent spin-wave theory based on Dyson-Maleev (DM) representation. Beside the nearest neighbor (NN) interaction within the plane, the planar frustration up to the third NNs, cyclic interaction and the interlayer coupling are taken into account. The detailed description of the elementary spin excitations, staggered magnetization, spin-wave velocity renormalization factor and ground state energy is given. The results are compared to the predictions of the linear spin-wave theory and when possible also to the second-order perturbative spin-wave expansion results. Finally, having at our disposal improved experimental results for the in-plane spin-wave dispersion in high-Tc copper oxide La2CuO4, the self-consistent spin-wave theory (SCSWT) is applied to that compound in order to correct earlier obtained set of exchange parameters and high-temperature spin-wave dispersion.

  2. Frustrated spin-1/2 molecular magnetism in the mixed-valence antiferromagnets Ba3M Ru2O9 (M =In , Y, Lu)

    Science.gov (United States)

    Ziat, D.; Aczel, A. A.; Sinclair, R.; Chen, Q.; Zhou, H. D.; Williams, T. J.; Stone, M. B.; Verrier, A.; Quilliam, J. A.

    2017-05-01

    We have performed magnetic susceptibility, heat capacity, muon spin relaxation, and neutron-scattering measurements on three members of the family Ba3M Ru2O9 , where M =In , Y, and Lu. These systems consist of mixed-valence Ru dimers on a triangular lattice with antiferromagnetic interdimer exchange. Although previous work has argued that charge order within the dimers or intradimer double exchange plays an important role in determining the magnetic properties, our results suggest that the dimers are better described as molecular units due to significant orbital hybridization, resulting in one spin-1/2 moment distributed equally over the two Ru sites. These molecular building blocks form a frustrated, quasi-two-dimensional triangular lattice. Our zero- and longitudinal-field μ SR results indicate that the molecular moments develop a collective, static magnetic ground state, with oscillations of the zero-field muon spin polarization indicative of long-range magnetic order in the Lu sample. The static magnetism is much more disordered in the Y and In samples, but they do not appear to be conventional spin glasses.

  3. Magnetic interactions in a quasi-one-dimensional antiferromagnet Cu(H{sub 2}O){sub 2}(en)SO{sub 4}

    Energy Technology Data Exchange (ETDEWEB)

    Sýkora, Rudolf, E-mail: rudolf.sykora@vsb.cz; Legut, Dominik [Nanotechnology Centre, VSB–Technical University of Ostrava, Ostrava 70833 (Czech Republic)

    2014-05-07

    A theoretical ab-initio investigation of exchange interaction between Cu atoms in an insulating antiferromagnet Cu(H{sub 2}O){sub 2}(en)SO{sub 4}, en = C{sub 2}H{sub 8}N{sub 2}, is reported. While the previous experimental studies described the system's magnetism to be quasi-two-dimensional, our results, based on a mapping of the system onto an effective Heisenberg model, rather support a quasi-one-dimensional character with the exchange coupling between the Cu atoms being propagated mainly along a zigzag line lying in the crystal's bc plane and connecting the Cu atoms through the N atoms. Further, the direction of magnetic moments on the Cu atoms is suggested to be nearly along the crystal's a axis. A check of the change in the exchange constants induced either by external pressure or by various values of U in the GGA + U approximation is made. Finally, based on experimental values of positions of broad maxima in magnetic-susceptibility and specific-heat curves and using theoretical expressions available in the literature a relevant value of the U parameter and related expected value of the electronic gap are estimated to be about 5 eV and 2 eV, respectively.

  4. Control of the third dimension in copper-based square-lattice antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Goddard, Paul A.; Singleton, John; Franke, Isabel; Möller, Johannes S.; Lancaster, Tom; Steele, Andrew J.; Topping, Craig V.; Blundell, Stephen J.; Pratt, Francis L.; Baines, C.; Bendix, Jesper; McDonald, Ross D.; Brambleby, Jamie; Lees, Martin R.; Lapidus, Saul H.; Stephens, Peter W.; Twamley, Brendan W.; Conner, Marianne M.; Funk, Kylee; Corbey, Jordan F.; Tran, Hope E.; Schlueter, J. A.; Manson, Jamie L.

    2016-03-01

    Using a mixed-ligand synthetic scheme, we create a family of quasi-two-dimensional antiferromagnets, namely, [Cu(HF2)(pyz)(2)]ClO4 [pyz = pyrazine], [CuL2(pyz)(2)](ClO4)(2) [L = pyO = pyridine-N-oxide and 4-phpy-O = 4-phenylpyridine-N-oxide. These materials are shown to possess equivalent two-dimensional [Cu(pyz)(2)](2+) nearly square layers, but exhibit interlayer spacings that vary from 6.5713 to 16.777 angstrom, as dictated by the axial ligands. We present the structural and magnetic properties of this family as determined via x-ray diffraction, electron-spin resonance, pulsed-and quasistatic-field magnetometry and muon-spin rotation, and compare them to those of the prototypical two-dimensional magnetic polymer Cu(pyz)(2)(ClO4)(2). We find that, within the limits of the experimental error, the two-dimensional, intralayer exchange coupling in our family of materials remains largely unaffected by the axial ligand substitution, while the observed magnetic ordering temperature (1.91 K for the material with the HF2 axial ligand, 1.70 K for the pyO and 1.63 K for the 4-phpy-O) decreases slowly with increasing layer separation. Despite the structural motifs common to this family and Cu(pyz)(2)(ClO4)(2), the latter has significantly stronger two-dimensional exchange interactions and hence a higher ordering temperature. We discuss these results, as well as the mechanisms that might drive the long-range order in these materials, in terms of departures from the ideal S = 1/2 two-dimensional square-lattice Heisenberg antiferromagnet. In particular, we find that both spin-exchange anisotropy in the intralayer interaction and interlayer couplings (exchange, dipolar, or both) are needed to account for the observed ordering temperatures, with the intralayer anisotropy becoming more important as the layers are pulled further apart.

  5. COMPUTER SIMULATION OF ANTIFERROMAGNETIC STRUCTURES DESCRIBED BY THE THREE-VERTEX ANTIFERROMAGNETIC POTTS MODEL

    National Research Council Canada - National Science Library

    Yarash K. Abuev; Albert B. Babaev; Pharkhat E. Esetov

    2017-01-01

    Objectives A computer simulation of the antiferromagnetic structures described by the three-vertex Potts model on a triangular lattice is performed, taking into account the antiferromagnetic exchange...

  6. Creation of an antiferromagnetic exchange spring

    Energy Technology Data Exchange (ETDEWEB)

    Scholl, A.; Liberati, M.; Arenholz, E.; Ohldag, H.; Stohr, J.

    2004-04-06

    We present evidence for the creation of an exchange spring in an antiferromagnet due to exchange coupling to a ferromagnet. X-ray magnetic linear dichroism spectroscopy on single crystal Co/NiO(001) shows that a partial domain wall is wound up at the surface of the antiferromagnet when the adjacent ferromagnet is rotated by a magnetic field. We determine the interface exchange stiffness and the antiferromagnetic domain wall energy from the field dependence of the direction of the antiferromagnetic axis, the antiferromagnetic pendant to a ferromagnetic hysteresis loop. The existence of a planar antiferromagnetic domain wall, proven by our measurement, is a key assumption of most exchange bias models.

  7. Antiferromagnetism in a Family of S = 1 Square Lattice Coordination Polymers NiX2(pyz)2 (X = Cl, Br, I, NCS; pyz = Pyrazine).

    Science.gov (United States)

    Liu, Junjie; Goddard, Paul A; Singleton, John; Brambleby, Jamie; Foronda, Francesca; Möller, Johannes S; Kohama, Yoshimitsu; Ghannadzadeh, Saman; Ardavan, Arzhang; Blundell, Stephen J; Lancaster, Tom; Xiao, Fan; Williams, Robert C; Pratt, Francis L; Baker, Peter J; Wierschem, Keola; Lapidus, Saul H; Stone, Kevin H; Stephens, Peter W; Bendix, Jesper; Woods, Toby J; Carreiro, Kimberly E; Tran, Hope E; Villa, Cecelia J; Manson, Jamie L

    2016-04-01

    The crystal structures of NiX2(pyz)2 (X = Cl (1), Br (2), I (3), and NCS (4)) were determined by synchrotron X-ray powder diffraction. All four compounds consist of two-dimensional (2D) square arrays self-assembled from octahedral NiN4X2 units that are bridged by pyz ligands. The 2D layered motifs displayed by 1-4 are relevant to bifluoride-bridged [Ni(HF2)(pyz)2]EF6 (E = P, Sb), which also possess the same 2D layers. In contrast, terminal X ligands occupy axial positions in 1-4 and cause a staggered packing of adjacent layers. Long-range antiferromagnetic (AFM) order occurs below 1.5 (Cl), 1.9 (Br and NCS), and 2.5 K (I) as determined by heat capacity and muon-spin relaxation. The single-ion anisotropy and g factor of 2, 3, and 4 were measured by electron-spin resonance with no evidence for zero-field splitting (ZFS) being observed. The magnetism of 1-4 spans the spectrum from quasi-two-dimensional (2D) to three-dimensional (3D) antiferromagnetism. Nearly identical results and thermodynamic features were obtained for 2 and 4 as shown by pulsed-field magnetization, magnetic susceptibility, as well as their Néel temperatures. Magnetization curves for 2 and 4 calculated by quantum Monte Carlo simulation also show excellent agreement with the pulsed-field data. Compound 3 is characterized as a 3D AFM with the interlayer interaction (J⊥) being slightly stronger than the intralayer interaction along Ni-pyz-Ni segments (J(pyz)) within the two-dimensional [Ni(pyz)2](2+) square planes. Regardless of X, J(pyz) is similar for the four compounds and is roughly 1 K.

  8. Thermophoresis of an antiferromagnetic soliton

    Science.gov (United States)

    Kim, Se Kwon; Tchernyshyov, Oleg; Tserkovnyak, Yaroslav

    2015-07-01

    We study the dynamics of an antiferromagnetic soliton under a temperature gradient. To this end, we start by phenomenologically constructing the stochastic Landau-Lifshitz-Gilbert equation for an antiferromagnet with the aid of the fluctuation-dissipation theorem. We then derive the Langevin equation for the soliton's center of mass by the collective coordinate approach. An antiferromagentic soliton behaves as a classical massive particle immersed in a viscous medium. By considering a thermodynamic ensemble of solitons, we obtain the Fokker-Planck equation, from which we extract the average drift velocity of a soliton. The diffusion coefficient is inversely proportional to a small damping constant α , which can yield a drift velocity of tens of m/s under a temperature gradient of 1 K/mm for a domain wall in an easy-axis antiferromagnetic wire with α ˜10-4 .

  9. A spin-1 kagome antiferromagnet

    Science.gov (United States)

    Tovar, Mayra; Shtengel, Kirill; Refael, Gil

    2010-03-01

    We study a spin-1 antiferromagnet on the kagom'e lattice. We start by constructing a Klein-type SU(2) symmetric Hamiltonian which contains Heisenberg interactions between nearest and next-nearest neighbors as well as three-body terms. Our model Hamiltonian has an extensive degenerate ground state whose manifold is spanned by the AKLT-like valence bond states. We also perturb the parent Hamiltonian by introducing an enhancement to the nearest neighbor antiferromagnetic Heisenberg interactions. By projecting this perturbation onto the basis spanned by the unperturbed ground states, we derive an effective Hamiltonian which is dual to that of the transverse field antiferromagnetic Ising model on the triangular lattice. Based on the parameters of our model, we find it to be in the order-by-disorder phase. The ground state is a valence bond crystal stabilized by quantum fluctuations. We also discuss excitations, both magnetic and non-magnetic, and address their possible relevance to experiment.

  10. Superconductivity, antiferromagnetism, and neutron scattering

    Science.gov (United States)

    Tranquada, John M.; Xu, Guangyong; Zaliznyak, Igor A.

    2014-01-01

    High-temperature superconductivity in both the copper-oxide and the iron-pnictide/chalcogenide systems occurs in close proximity to antiferromagnetically ordered states. Neutron scattering has been an essential technique for characterizing the spin correlations in the antiferromagnetic phases and for demonstrating how the spin fluctuations persist in the superconductors. While the nature of the spin correlations in the superconductors remains controversial, the neutron scattering measurements of magnetic excitations over broad ranges of energy and momentum transfers provide important constraints on the theoretical options. We present an overview of the neutron scattering work on high-temperature superconductors and discuss some of the outstanding issues.

  11. Spin diffusion and torques in disordered antiferromagnets

    KAUST Repository

    Manchon, Aurelien

    2017-02-01

    We have developed a drift-diffusion equation of spin transport in collinear bipartite metallic antiferromagnets. Starting from a model tight-binding Hamiltonian, we obtain the quantum kinetic equation within Keldysh formalism and expand it to the lowest order in spatial gradient using Wigner expansion method. In the diffusive limit, these equations track the spatio-temporal evolution of the spin accumulations and spin currents on each sublattice of the antiferromagnet. We use these equations to address the nature of the spin transfer torque in (i) a spin-valve composed of a ferromagnet and an antiferromagnet, (ii) a metallic bilayer consisting of an antiferromagnet adjacent to a heavy metal possessing spin Hall effect, and in (iii) a single antiferromagnet possessing spin Hall effect. We show that the latter can experience a self-torque thanks to the non-vanishing spin Hall effect in the antiferromagnet.

  12. Thermoinduced magnetization in nanoparticles of antiferromagnetic materials

    DEFF Research Database (Denmark)

    Mørup, Steen; Frandsen, Cathrine

    2004-01-01

    We show that there is a thermoinduced contribution to the magnetic moment of nanoparticles of antiferromagnetic materials. It arises from thermal excitations of the uniform spin-precession mode, and it has the unusual property that its magnitude increases with increasing temperature. This has...... the consequence that antiferromagnetism is nonexistent in nanoparticles at finite temperatures and it explains magnetic anomalies, which recently have been reported in a number of studies of nanoparticles of antiferromagnetic materials....

  13. Quantum Entanglement in Heisenberg Antiferromagnets

    CERN Document Server

    Subramanian, V

    2004-01-01

    Entanglement sharing among pairs of spins in Heisenberg antiferromagnets is investigated using the concurrence measure. For a nondegenerate S=0 ground state, a simple formula relates the concurrence to the diagonal correlation function. The concurrence length is seen to be extremely short. A few finite clusters are studied numerically, to see the trend in higher dimensions. It is argued that nearest-neighbour concurrence is zero for triangular and Kagome lattices. The concurrences in the maximal-spin states are explicitly calculated, where the concurrence averaged over all pairs is larger than the S=0 states.

  14. Quasiparticle excitations in frustrated antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Trumper, Adolfo E. [Instituto de Fisica Rosario (CONICET) Universidad Nacional de Rosario, Boulevard 27 de Febrero 210 bis, 2000 Rosario (Argentina)]. E-mail: trumper@ifir.edu.ar; Gazza, Claudio J. [Instituto de Fisica Rosario (CONICET) Universidad Nacional de Rosario, Boulevard 27 de Febrero 210 bis, 2000 Rosario (Argentina); Manuel, Luis O. [Instituto de Fisica Rosario (CONICET) Universidad Nacional de Rosario, Boulevard 27 de Febrero 210 bis, 2000 Rosario (Argentina)]. E-mail: manuel@ifir.edu.ar

    2004-12-31

    We have computed the quasiparticle wave function corresponding to a hole injected in a triangular antiferromagnet. We have taken into account multi-magnon contributions within the self-consistent Born approximation. We have found qualitative differences, under sign reversal of the integral transfer t, regarding the multi-magnon components and the own existence of the quasiparticle excitations. Such differences are due to the subtle interplay between magnon-assisted and free hopping mechanisms. We conclude that the conventional quasiparticle picture can be broken by geometrical frustration without invoking spin liquid phases.

  15. Purely antiferromagnetic magnetoelectric random access memory

    Science.gov (United States)

    Kosub, Tobias; Kopte, Martin; Hühne, Ruben; Appel, Patrick; Shields, Brendan; Maletinsky, Patrick; Hübner, René; Liedke, Maciej Oskar; Fassbender, Jürgen; Schmidt, Oliver G.; Makarov, Denys

    2017-01-01

    Magnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy efficiency. We propose and demonstrate a purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) that offers a remarkable 50-fold reduction of the writing threshold compared with ferromagnet-based counterparts, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal switching via gate voltage pulses and all-electric readout at room temperature. As no ferromagnetic component is present in the system, the writing magnetic field does not need to be pulsed for readout, allowing permanent magnets to be used. Based on our prototypes, we construct a comprehensive model of the magnetoelectric selection mechanisms in thin films of magnetoelectric antiferromagnets, revealing misfit induced ferrimagnetism as an important factor. Beyond memory applications, the AF-MERAM concept introduces a general all-electric interface for antiferromagnets and should find wide applicability in antiferromagnetic spintronics.

  16. Femtosecond optomagnetism in dielectric antiferromagnets

    Science.gov (United States)

    Bossini, D.; Rasing, Th

    2017-02-01

    Optical femtosecond manipulation of magnetic order is attractive for the development of new concepts for ultrafast magnetic recording. Theoretical and experimental investigations in this research area aim at establishing a physical understanding of magnetic media in light-induced non-equilibrium states. Such a quest requires one to adjust the theory of magnetism, since the thermodynamical concepts of elementary excitations and spin alignment determined by the exchange interaction are not applicable on the femtosecond time-scale after the photo-excitation. Here we report some key milestones concerning the femtosecond optical control of spins in dielectric antiferromagnets, whose spin dynamics is by nature faster than that of ferromagnets and can be triggered even without any laser heating. The recent progress of the opto-magnetic effect in the sub-wavelength regime makes this exciting research area even more promising, in terms of both fundamental breakthroughs and technological perspectives.

  17. Antiferromagnetic topological nodal line semimetals

    Science.gov (United States)

    Wang, Jing

    2017-08-01

    We study three-dimensional nodal line semimetals (NLSMs) with magnetic ordering and strong spin-orbit interaction. Two distinct classes of magnetic NLSMs are proposed. The first class is band-inversion NLSM where the accidental line node is induced by band inversion and locally protected by glide mirror plane and the combined time-reversal and inversion symmetries. This can be viewed as a trivial stacking of the two-dimensional antiferromagnetic Dirac semimetals. The second class is essential NLSM where the nodal features are filling enforced by specific magnetic symmetry group. We further provide two concrete tight-binding models for magnetic NLSMs which belong to these two different classes, respectively. We conclude with a brief discussion on the possible material venues and the experimental implications for such phases.

  18. Spatially anisotropic Heisenberg kagome antiferromagnet

    Science.gov (United States)

    Apel, W.; Yavors'kii, T.; Everts, H.-U.

    2007-04-01

    In the search for spin-1/2 kagome antiferromagnets, the mineral volborthite has recently been the subject of experimental studies (Hiroi et al 2001 J. Phys. Soc. Japan 70 3377; Fukaya et al 2003 Phys. Rev. Lett. 91 207603; Bert et al 2004 J. Phys.: Condens. Matter 16 S829; Bert et al 2005 Phys. Rev. Lett. 95 087203). It has been suggested that the magnetic properties of this material are described by a spin-1/2 Heisenberg model on the kagome lattice with spatially anisotropic exchange couplings. We report on investigations of the {\\mathrm {Sp}}(\\mathcal {N}) symmetric generalization of this model in the large \\mathcal {N} limit. We obtain a detailed description of the dependence of possible ground states on the anisotropy and on the spin length S. A fairly rich phase diagram with a ferrimagnetic phase, incommensurate phases with and without long-range order and a decoupled chain phase emerges.

  19. Quasi Two-Dimensional Dye-Sensitized In2O3 Phototransistors for Ultrahigh Responsivity and Photosensitivity Photodetector Applications.

    Science.gov (United States)

    Mottram, Alexander D; Lin, Yen-Hung; Pattanasattayavong, Pichaya; Zhao, Kui; Amassian, Aram; Anthopoulos, Thomas D

    2016-02-01

    We report the development of dye-sensitized thin-film phototransistors consisting of an ultrathin layer (92% in the wavelength range 400-700 nm. Importantly, the phototransistors are processed from solution-phase at temperatures below 200 °C hence making the technology compatible with inexpensive and temperature sensitive flexible substrate materials such as plastic.

  20. Quasi-two-dimensional quantum states of H{sub 2} in stage-2 Rb-intercalated graphite

    Energy Technology Data Exchange (ETDEWEB)

    Smith, A.P.; Benedek, R.; Trouw, F.R.; Minkoff, M. [Argonne National Lab., IL (United States); Yang, L.H. [Lawrence Livermore National Lab., CA (United States). Physics/H-Div.

    1995-10-30

    Inelastic-incoherent-neutron scattering can be a valuable nanostructural probe of H{sub 2}-doped porous materials, provided the spectral peaks can be interpreted in terms of crystal-field-split hydrogen-molecule energy levels, which represent a signature of the local symmetry. Inelastic-neutron-scattering measurements as well as extensive theoretical analyses have been performed on stage-2 Rb-intercalated graphite (Rb-GIC), with physisorbed H{sub 2}, HD, and D{sub 2}, a layered porous system with abundant spectral peaks, to assess whether the crystal-field-state picture enables a quantitative understanding of the observed structure. Potential-energy surfaces for molecular rotational and translational motion, as well as the intermolecular interactions of hydrogen molecules in Rb-GIC, were calculated within local-density-functional theory (LDFT). Model potentials, parameterized using results of the LDFT calculations, were employed in schematic calculations of rotational and translational excited state spectra of a single physisorbed H{sub 2} molecule in Rb-GIC. Results of the analysis are basically consistent with the assignment by Stead et al. of the lowest-lying peak at 1.4 meV to a rotational-tunneling transition of an isotropic hindered-rotor oriented normal to the planes, but indicate a small azimuthal anisotropy and a lower barrier than for the isotropic case. Based on the experimental isotope shifts and the theoretically predicted states, they conclude that spectral peaks at 11 and 22 meV are most likely related to center of mass excitations.

  1. Quasi Two-Dimensional Dye-Sensitized In 2 O 3 Phototransistors for Ultrahigh Responsivity and Photosensitivity Photodetector Applications

    KAUST Repository

    Mottram, Alexander D.

    2016-02-10

    © 2016 American Chemical Society. We report the development of dye-sensitized thin-film phototransistors consisting of an ultrathin layer (<10 nm) of indium oxide (In2O3) the surface of which is functionalized with a self-assembled monolayer of the light absorbing organic dye D102. The resulting transistors exhibit a preferential color photoresponse centered in the wavelength region of ∼500 nm with a maximum photosensitivity of ∼106 and a responsivity value of up to 2 × 103 A/W. The high photoresponse is attributed to internal signal gain and more precisely to charge carriers generated upon photoexcitation of the D102 dye which lead to the generation of free electrons in the semiconducting layer and to the high photoresponse measured. Due to the small amount of absorption of visible photons, the hybrid In2O3/D102 bilayer channel appears transparent with an average optical transmission of >92% in the wavelength range 400-700 nm. Importantly, the phototransistors are processed from solution-phase at temperatures below 200 °C hence making the technology compatible with inexpensive and temperature sensitive flexible substrate materials such as plastic.

  2. Numerical Simulation for Two-Phase Water Hammer Flows in Pipe by Quasi-Two-Dimensional Model

    Institute of Scientific and Technical Information of China (English)

    Tae Uk Jang; Yuebin Wu; Ying Xu; Qiang Sun

    2016-01-01

    The features of a quasi⁃two⁃dimensional ( quasi⁃2D) model for simulating two⁃phase water hammer flows with vaporous cavity in a pipe are investigated. The quasi⁃2D model with discrete vaporous cavity in the pipe is proposed in this paper. This model uses the quasi⁃2D model for pure liquid zone and one⁃dimensional ( 1D ) discrete vapor cavity model for vaporous cavity zone. The quasi⁃2D model solves two⁃dimensional equations for both axial and radial velocities and 1D equations for both pressure head and discharge by the method of characteristics. The 1D discrete vapor cavity model is used to simulate the vaporous cavity occurred when the pressure in the local pipe is lower than the vapor pressure of the liquid. The proposed model is used to simulate two⁃phase water flows caused by the rapid downstream valve closure in a reservoir⁃pipe⁃valve system. The results obtained by the proposed model are compared with those by the corresponding 1D model and the experimental ones provided by the literature, respectively. The comparison shows that the maximum pressure heads simulated by the proposed model are more accurate than those by the corresponding 1D model.

  3. De Haas-van Alphen Oscillations In Quasi-two-dimensional Underdoped Cuprate Superconductors In The Canonical Ensemble

    Energy Technology Data Exchange (ETDEWEB)

    Harrison, N [Los Alamos National Laboratory; Sebastian, S E [CAMBRIDGE UNIV.

    2008-01-01

    We calculate the de Haas-van Alphen (dHvA) effect waveform using the canonical ensemble for different Fermi surface scenarios applicable to the underdoped cuprate superconductor YBa{sub 2}Cu{sub 3}O{sub 6.5}, in which quantum oscillations have recently been observed. The harmonic content of the dHvA waveform of the principal F{sub {alpha}} {approx} 500 T frequency is consistent with the existence of a second thermodynamically dominant section of Fermi surface that acts primarily as a charge reservoir. Oscillations in the charge density to and from this reservoir are shown to potentially contribute to the observed large quantum oscillations in the Hall resistance.

  4. Mapping the directional emission of quasi-two-dimensional photonic crystals of semiconductor nanowires using Fourier microscopy

    NARCIS (Netherlands)

    Fontana, Y.; Grzela, G.; Bakkers, E.P.A.M.; Gomez Rivas, J.

    2012-01-01

    Controlling the dispersion and directionality of the emission of nanosources is one of the major goals of nanophotonics research. This control will allow the development of highly efficient nanosources even at the single-photon level. One of the ways to achieve this goal is to couple the emission to

  5. Slow Oscillations of In-plane Magnetoresistance in Strongly Anisotropic Quasi-Two-Dimensional Rare-Earth Tritellurides

    Science.gov (United States)

    Sinchenko, A. A.; Grigoriev, P. D.; Monceau, P.; Lejay, P.; Zverev, V. N.

    2016-12-01

    The slow oscillations of intralayer magnetoresistance in the quasi-2D metallic compounds TbTe_3 and GdTe_3 have been observed for the first time. These oscillations do not originate from small Fermi-surface pockets, as revealed usually by Shubnikov-de Haas oscillations, but from the entanglement of close frequencies due to a finite interlayer transfer integral t_z, either between the two Te planes forming a bilayer or between two adjacent bilayers, which allows to estimate its values. For TbTe_3 and GdTe_3, we obtain the estimate t_ z≈ 1 meV.

  6. Magnetothermopower study of the quasi-two-dimensional organic conductor α-(BEDT-TTF)2KHg(SCN)4

    Science.gov (United States)

    Choi, E. S.; Brooks, J. S.; Qualls, J. S.

    2002-05-01

    We have used a low-frequency magneto-thermopower (MTEP) method to probe the high-magnetic-field ground-state behavior of α-(BEDT-TTF)2KHg(SCN)4 along all three principal crystallographic axes at low temperatures. The thermopower tensor coefficients (Sxx,Syx, and Szz) have been measured to 30 T, beyond the anomalous low-temperature, field-induced transition at 22.5 T. We find a significant anisotropy in the MTEP signal, and also observe large quantum oscillations associated with Landau quantization. The anisotropy indicates that the ground-state properties are clearly driven by mechanisms that occur along specific directions for the in-plane electronic structure. Both transverse and longitudinal magnetothermopower show asymptotic behaviors in the field, which can be explained in terms of magnetic breakdown of compensated closed orbits.

  7. Divergence of the Long Wavelength Collective Diffusion Coefficient in Quasi-one and Quasi-two Dimensional Colloid Suspensions

    Science.gov (United States)

    Lin, Binhua; Cui, Bianxiao; Xu, Xinliang; Zangi, Ronen; Diamant, Haim; Rice, Stuart A.

    2015-03-01

    We report the results of experimental studies of the short time-long wavelength behavior of collective particle displacements in q1D and q2D colloid suspensions. Our results are reported via the q->0 behavior of the hydrodynamic function H (q) that relates the effective collective diffusion coefficient, De (q) , with the static structure factor S (q) and the self-diffusion coefficient of isolated particles Do: H (q) De (q) S (q) /Do. We find an apparent divergence of H (q) as q->0 with the form H(q)q-(1.7 qualitatively different from that of the three-dimensional H (q) and De (q) as q->0, and the divergence is of a different functional form from that predicted for the diffusion coefficient in one component 1D and 2D fluids not subject to boundary conditions that define the dimensionality of the system. The research was supported by the NSF MRSEC at the U of Chicago (NSF/DMR-MRSEC 0820054), NSF/CHE 0822838 (ChemMatCARS), and Israel Science Foundation (Grant No. 8/10).

  8. Quasi-two-dimensional electronic properties of the sodium molybdenum bronze, Na 0.9Mo 6O 17

    Science.gov (United States)

    Greenblatt, M.; Ramanujachary, K. V.; McCarroll, W. H.; Neifeld, R.; Waszczak, J. V.

    1985-09-01

    Four probe electrical resistivity measurements between 1.5 and 300 K were made on single crystals of the violet-red bronze Na 0.9Mo 6O 17 grown by a temperature gradient flux technique. The temperature variation of the resistivity shows metallic conductivity and highly anisotropic behavior similar to K 0.9Mo 6O 17 and Li 0.9Mo 6O 17. The room-temperature resistivity, measured in the direction parallel to the plate axis, is 3.0 × 10 -3 Ω cm and perpendicular to that axis it is 0.21 Ω cm. A transition observed at ˜88 K is possibly related to the onset of a charge density wave. The temperature variation of the susceptibility show Pauli paramagnetic behavior at high temperature, and highly anomalous behavior in the vicinity of the transition at low temperatures.

  9. Quasi two-dimensional electronic properties of the lithium molybdenum bronze, Li 0.9Mo 6O 17

    Science.gov (United States)

    Greenblatt, M.; McCarroll, W. H.; Neifeld, R.; Croft, M.; Waszczak, J. V.

    1984-09-01

    Four probe electrical resistivity measurements between 0.3K and 300K were made on single crystals of the violet-red bronze Li 0.9Mo 6O 17 grown by a temperature gradient flux technique. The temperature variation of the resistivity shows metallic conductivity and highly anisotropic behavior similar to K 0.9Mo 6O 17. The room temperature resistivity, measured in the direction parallel to the plate axis, is 9.5×10 -3Ωcm and 2.47Ωcm perpendicular to that axis. A phase transition observed at ˜24K is possibly related to the onset of a charge density wave. A transition to the superconducting state is observed at Tc ˜ 1.9K.

  10. Transient terahertz spectroscopy of excitons and unbound carriers in quasi two-dimensional electron-hole gases

    Energy Technology Data Exchange (ETDEWEB)

    Kaindl, Robert A.; Hagele, D.; Carnahan, M. A.; Chemla, D. S.

    2008-09-11

    We report a comprehensive experimental study and detailed model analysis of the terahertz (THz) dielectric response and density kinetics of excitons and unbound electron-hole pairs in GaAs quantum wells. A compact expression is given, in absolute units, for the complex-valued THz dielectric function of intra-excitonic transitions between the 1s and higher-energy exciton and continuum levels. It closely describes the THz spectra of resonantly generated excitons. Exciton ionization and formation are further explored, where the THz response exhibits both intra-excitonic and Drude features. Utilizing a two-component dielectric function, we derive the underlying exciton and unbound pair densities. In the ionized state, excellent agreement is found with the Saha thermodynamic equilibrium, which provides experimental verification of the two-component analysis and density scaling. During exciton formation, in turn, the pair kinetics is quantitatively described by a Saha equilibrium that follows the carrier cooling dynamics. The THz-derived kinetics is, moreover, consistent with time-resolved luminescence measured for comparison. Our study establishes a basis for tracking pair densities via transient THz spectroscopy of photoexcited quasi-2D electron-hole gases.

  11. Exponential suppression of interlayer conductivity in very anisotropic quasi-two-dimensional compounds in high magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Grigoriev, P.D., E-mail: grigorev@itp.ac.ru [L. D. Landau Institute for Theoretical Physics, Chernogolovka (Russian Federation)

    2012-06-01

    It is shown that in rather strong magnetic field the interlayer electron conductivity is exponentially damped by the Coulomb barrier arising from the formation of polaron around each localized electron state. The theoretical model is developed to describe this effect, and the calculation of the temperature and field dependence of interlayer magnetoresistance is performed. The results obtained agree well with the experimental data in GaAs/AlGaAs heterostructures and in strongly anisotropic organic metals. The proposed theory allows to use the experiments on interlayer magnetoresistance to investigate the electron states, localized by magnetic field and disorder.

  12. Spin-phonon interaction in antiferromagnetics

    Energy Technology Data Exchange (ETDEWEB)

    Grigorashchuk, I.M.; Nitsovich, V.M.; Tovstyuk, K.D.

    1975-01-01

    The vibrational spectrum and the sound velocity in antiferromagnetics are obtained in the general form in pseudoharmonic approximation with allowance for the anharmonisms of all orders. Starting from experimentally defined dependence of the Debye-Waller factor on the temperature a corollary is put forward that in some antiferromagnetics under the temperature lower than T/subN/ the appearance of the narrow band of paramagnetic states is possible. In antiferromagnetics where the transition metal-dielectric described by the Habbard model is possible this results in the appearance of the additional transition dielectric-metal-dielectric. (auth)

  13. The rotational anisotropies in the ferromagnetism/antiferromagnetism 1/antiferromagnetism 2 exchange bias structures

    Institute of Scientific and Technical Information of China (English)

    Hu Jing-Guo; Stamps R L

    2006-01-01

    The rotational anisotropies in the exchange bias structures of ferromagnetism/antiferromagnetism 1/antiferromagnetism 2 are studied in this paper. Based on the model, in which the antiferromagnetism is treated with an Ising mean field theory and the rotational anisotropy is assumed to be related to the field created by the moment induced on the antiferromagnetic layer next to the ferromagnetic layer, we can explain why in experiments for ferromagnetism (FM)/antiferromagntism 1 (AFM1)/antiferromagnetism 2 (AFM2) systems the thickness-dependent rotational anisotropy value is non-monotonic, i.e. it reaches a minimum for this system at a specific thickness of the first antiferromagnetic layer and exhibits oscillatory behaviour. In addition, we find that the temperature-dependent rotational anisotropy value is in good agreement with the experimental result.

  14. Dynamic rotor mode in antiferromagnetic nanoparticles

    DEFF Research Database (Denmark)

    Lefmann, Kim; Jacobsen, H.; Garde, J.

    2015-01-01

    We present experimental, numerical, and theoretical evidence for an unusual mode of antiferromagnetic dynamics in nanoparticles. Elastic neutron scattering experiments on 8-nm particles of hematite display a loss of diffraction intensity with temperature, the intensity vanishing around 150 K...

  15. Antiferromagnetic domain wall motion driven by spin-orbit torques

    Science.gov (United States)

    Shiino, Takayuki; Oh, Se-Hyeok; Haney, Paul M.; Lee, Seo-Won; Go, Gyungchoon; Park, Byong-Guk; Lee, Kyung-Jin

    2016-01-01

    We theoretically investigate dynamics of antiferromagnetic domain walls driven by spin-orbit torques in antiferromagnet/heavy metal bilayers. We show that spin-orbit torques drive antiferromagnetic domain walls much faster than ferromagnetic domain walls. As the domain wall velocity approaches the maximum spin-wave group velocity, the domain wall undergoes Lorentz contraction and emits spin-waves in the terahertz frequency range. The interplay between spin-orbit torques and the relativistic dynamics of antiferromagnetic domain walls leads to the efficient manipulation of antiferromagnetic spin textures and paves the way for the generation of high frequency signals from antiferromagnets. PMID:27588878

  16. Purely antiferromagnetic magnetoelectric random access memory

    Science.gov (United States)

    Kosub, Tobias; Kopte, Martin; Hühne, Ruben; Appel, Patrick; Shields, Brendan; Maletinsky, Patrick; Hübner, René; Liedke, Maciej Oskar; Fassbender, Jürgen; Schmidt, Oliver G.; Makarov, Denys

    2017-01-01

    Magnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy efficiency. We propose and demonstrate a purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) that offers a remarkable 50-fold reduction of the writing threshold compared with ferromagnet-based counterparts, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal switching via gate voltage pulses and all-electric readout at room temperature. As no ferromagnetic component is present in the system, the writing magnetic field does not need to be pulsed for readout, allowing permanent magnets to be used. Based on our prototypes, we construct a comprehensive model of the magnetoelectric selection mechanisms in thin films of magnetoelectric antiferromagnets, revealing misfit induced ferrimagnetism as an important factor. Beyond memory applications, the AF-MERAM concept introduces a general all-electric interface for antiferromagnets and should find wide applicability in antiferromagnetic spintronics. PMID:28045029

  17. Paramagnetic and Antiferromagnetic Spin Seebeck Effect

    Science.gov (United States)

    Wu, Stephen

    We report on the observation of the longitudinal spin Seebeck effect in both antiferromagnetic and paramagnetic insulators. By using a microscale on-chip local heater, it is possible to generate a large thermal gradient confined to the chip surface without a large increase in the total sample temperature. This technique allows us to easily access low temperatures (200 mK) and high magnetic fields (14 T) through conventional dilution refrigeration and superconducting magnet setups. By exploring this regime, we detect the spin Seebeck effect through the spin-flop transition in antiferromagnetic MnF2 when a large magnetic field (>9 T) is applied along the easy axis direction. Using the same technique, we are also able to resolve a spin Seebeck effect from the paramagnetic phase of geometrically frustrated antiferromagnet Gd3Ga5O12 (gadolinium gallium garnet) and antiferromagnetic DyScO3 (DSO). Since these measurements occur above the ordering temperatures of these two materials, short-range magnetic order is implicated as the cause of the spin Seebeck effect in these systems. The discovery of the spin Seebeck effect in these two materials classes suggest that both antiferromagnetic spin waves and spin excitations from short range magnetic order may be used to generate spin current from insulators and that the spin wave spectra of individual materials are highly important to the specifics of the longitudinal spin Seebeck effect. Since insulating antiferromagnets and paramagnets are far more common than the typical insulating ferrimagnetic materials used in spin Seebeck experiments, this discovery opens up a large new class of materials for use in spin caloritronic devices. All authors acknowledge support of the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division. The use of facilities at the Center for Nanoscale Materials, was supported by the U.S. DOE, BES under Contract No. DE-AC02-06CH11357.

  18. Antiferromagnetic Ising model on the swedenborgite lattice

    NARCIS (Netherlands)

    Buhrandt, Stefan; Fritz, Lars

    2014-01-01

    Geometrical frustration in spin systems often results in a large number of degenerate ground states. In this work, we study the antiferromagnetic Ising model on the three-dimensional swedenborgite lattice, which is a specific stacking of kagome and triangular layers. The model contains two exchange

  19. Magnetic remanent states in antiferromagnetically coupled multilayers

    Energy Technology Data Exchange (ETDEWEB)

    Kiselev, N.S., E-mail: m.kyselov@ifw-dresden.d [IFW Dresden, Postfach 270116, D-01171 Dresden (Germany); Donetsk Institute for Physics and Technology, 83114 Donetsk (Ukraine); Roessler, U.K.; Bogdanov, A.N. [IFW Dresden, Postfach 270116, D-01171 Dresden (Germany); Hellwig, O. [San Jose Research Center, Hitachi Global Storage Technologies, San Jose, CA 95135 (United States)

    2010-05-15

    In antiferromagnetically coupled multilayers with perpendicular anisotropy unusual multidomain textures can be stabilized due to a close competition between long-range demagnetization fields and short-range interlayer exchange coupling. In particular, the formation and evolution of specific topologically stable planar defects within the antiferromagnetic ground state, i.e. wall-like structures with a ferromagnetic configuration extended over a finite width, explain configurational hysteresis phenomena recently observed in [Co/Pt(Pd)]/Ru and [Co/Pt]/NiO multilayers. Within a phenomenological theory, we have analytically derived the equilibrium sizes of these 'ferroband' defects as functions of the antiferromagnetic exchange, a bias magnetic field, and geometrical parameters of the multilayers. In the magnetic phase diagram, the existence region of the ferrobands mediates between the regions of patterns with sharp antiferromagnetic domain walls and regular arrays of ferromagnetic stripes. The theoretical results are supported by magnetic force microscopy images of the remanent states observed in [Co/Pt]/Ru.

  20. Direct measurement of antiferromagnetic domain fluctuations.

    Energy Technology Data Exchange (ETDEWEB)

    Shpyrko, O. G.; Isaacs, E. D.; Logan, J. M.; Feng, Y.; Aeppli, G.; Jaramillo, R.; Kim, H. C.; Rosenbaum, T. F.; Zschack, P.; Sprung, M.; Narayanan, S.; Sandy, A.; Univ. of Chicago; Univ. College London

    2007-05-03

    Measurements of magnetic noise emanating from ferromagnets owing to domain motion were first carried out nearly 100 years ago1, and have underpinned much science and technology2, 3. Antiferromagnets, which carry no net external magnetic dipole moment, yet have a periodic arrangement of the electron spins extending over macroscopic distances, should also display magnetic noise. However, this must be sampled at spatial wavelengths of the order of several interatomic spacings, rather than the macroscopic scales characteristic of ferromagnets. Here we present a direct measurement of the fluctuations in the nanometer-scale superstructure of spin- and charge-density waves associated with antiferromagnetism in elemental chromium. The technique used is X-ray photon correlation spectroscopy, where coherent X-ray diffraction produces a speckle pattern that serves as a 'fingerprint' of a particular magnetic domain configuration. The temporal evolution of the patterns corresponds to domain walls advancing and retreating over micrometer distances. This work demonstrates a useful measurement tool for antiferromagnetic domain wall engineering, but also reveals a fundamental finding about spin dynamics in the simplest antiferromagnet: although the domain wall motion is thermally activated at temperatures above 100 K, it is not so at lower temperatures, and indeed has a rate that saturates at a finite value--consistent with quantum fluctuations--on cooling below 40 K.

  1. Antiferromagnetism in chromium alloy single crystals

    DEFF Research Database (Denmark)

    Bjerrum Møller, Hans; Trego, A.L.; Mackintosh, A.R.

    1965-01-01

    The antiferromagnetism of single crystals of dilute alloys of V, Mn and Re in Cr has been studied at 95°K and 300°K by neutron diffraction. The addition of V causes the diffraction peaks to decrease in intensity and move away from (100), while Mn and Re cause them to increase and approach (100) so...

  2. The electronic structure of antiferromagnetic chromium

    DEFF Research Database (Denmark)

    Skriver, Hans Lomholt

    1981-01-01

    The author has used the local spin density formalism to perform self-consistent calculations of the electronic structure of chromium in the non-magnetic and commensurate antiferromagnetic phases, as a function of the lattice parameter. A change of a few per cent in the atomic radius brings...

  3. Macroscopic Quantum Coherence in Antiferromagnetic Molecular Magnets

    Institute of Scientific and Technical Information of China (English)

    HU Hui; LO Rong; ZHU Jia-Lin; XIONG Jia-Jiong

    2001-01-01

    The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model. On the basis of instanton technique in the spin-coherent-state path-integral representation, both the rigorous Wentzel-Kramers-Brillouin exponent and pre-exponential factor for the ground-state tunnel splitting are obtained. We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys. Rev. Lett. 80 (1998) 169), but also have great influence on the intensity of the ground-state tunnel splitting. Those features clearly have no analogue in the ferromagnetic molecular magnets. We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets. The analytical results are complemented by exact diagonalization calculation.

  4. Antiferromagnetic Ising Model in Hierarchical Networks

    Science.gov (United States)

    Cheng, Xiang; Boettcher, Stefan

    2015-03-01

    The Ising antiferromagnet is a convenient model of glassy dynamics. It can introduce geometric frustrations and may give rise to a spin glass phase and glassy relaxation at low temperatures [ 1 ] . We apply the antiferromagnetic Ising model to 3 hierarchical networks which share features of both small world networks and regular lattices. Their recursive and fixed structures make them suitable for exact renormalization group analysis as well as numerical simulations. We first explore the dynamical behaviors using simulated annealing and discover an extremely slow relaxation at low temperatures. Then we employ the Wang-Landau algorithm to investigate the energy landscape and the corresponding equilibrium behaviors for different system sizes. Besides the Monte Carlo methods, renormalization group [ 2 ] is used to study the equilibrium properties in the thermodynamic limit and to compare with the results from simulated annealing and Wang-Landau sampling. Supported through NSF Grant DMR-1207431.

  5. Antiferromagnetic order in hybrid electromagnetic metamaterials

    Science.gov (United States)

    Miroshnichenko, Andrey E.; Filonov, Dmitry; Lukyanchuk, Boris; Kivshar, Yuri

    2017-08-01

    We demonstrate experimentally a new type of order in optical magnetism resembling the staggered structure of spins in antiferromagnetic ordered materials. We study hybrid electromagnetic metasurfaces created by assembling hybrid meta-atoms formed by metallic split-ring resonators and dielectric particles with a high refractive index, both supporting optically-induced magnetic dipole resonances of different origin. Each pair (or ‘metamolecule’) is characterized by two interacting magnetic dipole moments with the distance-dependent magnetization resembling the spin exchange interaction in magnetic materials. By directly mapping the structure of the electromagnetic fields, we demonstrate experimentally that strong coupling between the optically-induced magnetic moments of different origin can flip the magnetisation orientation in a metamolecule creating an antiferromagnetic lattice of staggered optically-induced magnetic moments in hybrid metasurfaces.

  6. Antiferromagnetic exchange mechanism of superconductivity in cuprates

    CERN Document Server

    Plakida, N M

    2001-01-01

    One examines theory of superconducting coupling resulted from antiferromagnetic exchange in terms of which one explains strong dependence of T sub c superconducting transition temperature on alpha lattice constant. Calculations are based on the Hubbard p-d two-region model within strong correlation limit. DELTA pd excitation high energy at antiferromagnetic exchange of two particles from different Hubbard subregions results in suppression o delay effects and in coupling of all particles in conductivity subregion with Fermi energy E sub F >= DELTA pd : T sub c approx = E sub F exp(-1/lambda), where lambda propor to J. T sub c (alpha) and isotopic effect are explained by J exchange interaction dependence on alpha and on zero oscillations of oxygen ions

  7. Macroscopic Quantum Coherence in Antiferromagnetic Molecular Magnets

    Institute of Scientific and Technical Information of China (English)

    HUHui; LURong; 等

    2001-01-01

    The macroscopic quantum coherence in a biaxial antiferromagnetic molecular magnet in the presence of magnetic field acting parallel to its hard anisotropy axis is studied within the two-sublattice model.On the basis of instanton technique in the spin-coherent-state path-integral representation,both the rigorous Wentzel-Kramers-Brillouin exponent and pre-exponential factor for the ground-state tunnel splitting are obtained.We find that the quantum fluctuations around the classical paths can not only induce a new quantum phase previously reported by Chiolero and Loss (Phys.Rev.Lett.80(1998)169),but also have great influence on the intensity of the ground-state tunnel splitting.Those features clearly have no analogue in the ferromagnetic molecular magnets.We suggest that they may be the universal behaviors in all antiferromagnetic molecular magnets.The analytical results are complemented by exact diagonalization calculation.

  8. Shape-induced anisotropy in antiferromagnetic nanoparticles

    OpenAIRE

    H. Gomonay; Kondovych, S.; Loktev, V.

    2013-01-01

    High fraction of the surface atoms considerably enhances the influence of size and shape on the magnetic and electronic properties of nanoparticles. Shape effects in ferromagnetic nanoparticles are well understood and allow to set and control the parameters of a sample that affect its magnetic anisotropy during production. In the present paper we study the shape effects in the other widely used magnetic materials -- antiferromagnets, -- which possess vanishingly small or zero macroscopic magn...

  9. Spin-Mechanical Inertia in Antiferromagnet

    OpenAIRE

    2016-01-01

    The conservation of angular momentum has served as a guiding principle in the coupled dynamics of quantum spins and mechanical rotations. However, in an antiferromagnet with vanishing magnetization, new fundamental rules are required to properly describe spin-mechanical phenomena. Here we demonstrate that the Neel order dynamics affects the mechanical motion of a rigid body by modifying its inertia tensor in the presence of strong magnetocrystalline anisotropy. This effect depends on temperat...

  10. Spin Transport in Ferromagnetic and Antiferromagnetic Textures

    KAUST Repository

    Akosa, Collins A.

    2016-12-07

    In this dissertation, we provide an accurate description of spin transport in magnetic textures and in particular, we investigate in detail, the nature of spin torque and magnetic damping in such systems. Indeed, as will be further discussed in this thesis, the current-driven velocity of magnetic textures is related to the ratio between the so-called non-adiabatic torque and magnetic damping. Uncovering the physics underlying these phenomena can lead to the optimal design of magnetic systems with improved efficiency. We identified three interesting classes of systems which have attracted enormous research interest (i) Magnetic textures in systems with broken inversion symmetry: We investigate the nature of magnetic damping in non-centrosymmetric ferromagnets. Based on phenomenological and microscopic derivations, we show that the magnetic damping becomes chiral, i.e. depends on the chirality of the magnetic texture. (ii) Ferromagnetic domain walls, skyrmions and vortices: We address the physics of spin transport in sharp disordered magnetic domain walls and vortex cores. We demonstrate that upon spin-independent scattering, the non-adiabatic torque can be significantly enhanced. Such an enhancement is large for vortex cores compared to transverse domain walls. We also show that the topological spin currents owing in these structures dramatically enhances the non-adiabaticity, an effect unique to non-trivial topological textures (iii) Antiferromagnetic skyrmions: We extend this study to antiferromagnetic skyrmions and show that such an enhanced topological torque also exist in these systems. Even more interestingly, while such a non-adiabatic torque inuences the undesirable transverse velocity of ferromagnetic skyrmions, in antiferromagnetic skyrmions, the topological non-adiabatic torque directly determines the longitudinal velocity. As a consequence, scaling down the antiferromagnetic skyrmion results in a much more efficient spin torque.

  11. Spin transfer in antiferromagnets (Conference Presentation)

    Science.gov (United States)

    Moriyama, Takahiro

    2016-10-01

    Since antiferromagnets (AFMs) have no spontaneous magnetization unlike ferromagnetic materials, it is not easy to manipulate the magnetic moments in AFMs by external magnetic field. However, recent theoretical studies suggest that it is possible to manipulate the magnetization in AFMs by spin-transfer-torque in a similar manner to ferromagnetic materials. In this study, we perform spin-toque ferromagnetic resonance (ST-FMR) measurements on FeNi/NiO/Pt multilayers to experimentally investigate the interaction between the spin current and the magnetic moments of antiferromagnetic NiO. The spin current is injected to the NiO by the spin Hall effect in Pt. The monotonous change in the FMR linewidth of this system with respect to the spin current can be interpreted in a way that the spin current is transferred through the NiO and interacts with the FeNi. This intriguing spin current transport can be explained by the angular momentum transfer mediated by the antiferromagnetic magnons. The results assure that the spin current exerts a torque on the NiO magnetic moments and excites their dynamics. In the talk, recent results will be also discussed.

  12. Spin Seebeck Effect Signals from Antiferromagnets

    Science.gov (United States)

    Prakash, Arati; Brangham, Jack; Yang, Fengyuan; Heremans, Joseph

    The Longitudinal Spin Seebeck Effect (LSSE), in which a heat current stimulates spin propagation across an interface between a magnetic material and a normal metal, is well established and observed in ferromagnetic systems. Data have been presented indicating that antiferromagnetic systems could also give rise to LSSE signals. We report here on LSSE signal measured on the Pt/NiO/YIG structure, where NiO is an antiferromagnet. This system is reported to exhibit antiferromagnonic transport. We explore the dependence of the signal on the thickness of the NiO and YIG layers. We also report its temperature dependence, which was not explored before. The results are interpreted in terms of the temperature dependence of the magnon density of states. It appears that magnon modes with energies below about 40 K are most involved in the process, as was the case to the LSSE on YIG itself. Preliminary results using other antiferromagnets and other inverse spin-Hall layers look promising and will also be reported Work supported by ARO- MURI W911NF-14-1-0016.

  13. Model calculation of thermal conductivity in antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Mikhail, I.F.I., E-mail: ifi_mikhail@hotmail.com; Ismail, I.M.M.; Ameen, M.

    2015-11-01

    A theoretical study is given of thermal conductivity in antiferromagnetic materials. The study has the advantage that the three-phonon interactions as well as the magnon phonon interactions have been represented by model operators that preserve the important properties of the exact collision operators. A new expression for thermal conductivity has been derived that involves the same terms obtained in our previous work in addition to two new terms. These two terms represent the conservation and quasi-conservation of wavevector that occur in the three-phonon Normal and Umklapp processes respectively. They gave appreciable contributions to the thermal conductivity and have led to an excellent quantitative agreement with the experimental measurements of the antiferromagnet FeCl{sub 2}. - Highlights: • The Boltzmann equations of phonons and magnons in antiferromagnets have been studied. • Model operators have been used to represent the magnon–phonon and three-phonon interactions. • The models possess the same important properties as the exact operators. • A new expression for the thermal conductivity has been derived. • The results showed a good quantitative agreement with the experimental data of FeCl{sub 2}.

  14. Functional renormalization for antiferromagnetism and superconductivity in the Hubbard model

    Energy Technology Data Exchange (ETDEWEB)

    Friederich, Simon

    2010-12-08

    Despite its apparent simplicity, the two-dimensional Hubbard model for locally interacting fermions on a square lattice is widely considered as a promising approach for the understanding of Cooper pair formation in the quasi two-dimensional high-T{sub c} cuprate materials. In the present work this model is investigated by means of the functional renormalization group, based on an exact flow equation for the effective average action. In addition to the fermionic degrees of freedom of the Hubbard Hamiltonian, bosonic fields are introduced which correspond to the different possible collective orders of the system, for example magnetism and superconductivity. The interactions between bosons and fermions are determined by means of the method of ''rebosonization'' (or ''flowing bosonization''), which can be described as a continuous, scale-dependent Hubbard-Stratonovich transformation. This method allows an efficient parameterization of the momentum-dependent effective two-particle interaction between fermions (four-point vertex), and it makes it possible to follow the flow of the running couplings into the regimes exhibiting spontaneous symmetry breaking, where bosonic fluctuations determine the types of order which are present on large length scales. Numerical results for the phase diagram are presented, which include the mutual influence of different, competing types of order. (orig.)

  15. Robust spin transfer torque in antiferromagnetic tunnel junctions

    KAUST Repository

    Saidaoui, Hamed Ben Mohamed

    2017-04-18

    We theoretically study the current-induced spin torque in antiferromagnetic tunnel junctions, composed of two semi-infinite antiferromagnetic layers separated by a tunnel barrier, in both clean and disordered regimes. We find that the torque enabling electrical manipulation of the Néel antiferromagnetic order parameter is out of plane, ∼n×p, while the torque competing with the antiferromagnetic exchange is in plane, ∼n×(p×n). Here, p and n are the Néel order parameter direction of the reference and free layers, respectively. Their bias dependence shows behavior similar to that in ferromagnetic tunnel junctions, the in-plane torque being mostly linear in bias, while the out-of-plane torque is quadratic. Most importantly, we find that the spin transfer torque in antiferromagnetic tunnel junctions is much more robust against disorder than that in antiferromagnetic metallic spin valves due to the tunneling nature of spin transport.

  16. Dynamic magnetic hysteresis and nonlinear susceptibility of antiferromagnetic nanoparticles

    Science.gov (United States)

    Kalmykov, Yuri P.; Ouari, Bachir; Titov, Serguey V.

    2016-08-01

    The nonlinear ac stationary response of antiferromagnetic nanoparticles subjected to both external ac and dc fields of arbitrary strength and orientation is investigated using Brown's continuous diffusion model. The nonlinear complex susceptibility and dynamic magnetic hysteresis (DMH) loops of an individual antiferromagnetic nanoparticle are evaluated and compared with the linear regime for extensive ranges of the anisotropy, the ac and dc magnetic fields, damping, and the specific antiferromagnetic parameter. It is shown that the shape and area of the DMH loops of antiferromagnetic particles are substantially altered by applying a dc field that permits tuning of the specific magnetic power loss in the nanoparticles.

  17. Dynamics of antiferromagnetic skyrmion driven by the spin Hall effect

    Science.gov (United States)

    Jin, Chendong; Song, Chengkun; Wang, Jianbo; Liu, Qingfang

    2016-10-01

    Magnetic skyrmion moved by the spin-Hall effect is promising for the application of the generation racetrack memories. However, the Magnus force causes a deflected motion of skyrmion, which limits its application. Here, we create an antiferromagnetic skyrmion by injecting a spin-polarized pulse in the nanostripe and investigate the spin Hall effect-induced motion of antiferromagnetic skyrmion by micromagnetic simulations. In contrast to ferromagnetic skyrmion, we find that the antiferromagnetic skyrmion has three evident advantages: (i) the minimum driving current density of antiferromagnetic skyrmion is about two orders smaller than the ferromagnetic skyrmion; (ii) the velocity of the antiferromagnetic skyrmion is about 57 times larger than the ferromagnetic skyrmion driven by the same value of current density; (iii) antiferromagnetic skyrmion can be driven by the spin Hall effect without the influence of Magnus force. In addition, antiferromagnetic skyrmion can move around the pinning sites due to its property of topological protection. Our results present the understanding of antiferromagnetic skyrmion motion driven by the spin Hall effect and may also contribute to the development of antiferromagnetic skyrmion-based racetrack memories.

  18. Energy Method of Finding Distribution Constants of an Antiferromagnetic Vector for an Antidot System in a Two-sublattice Antiferromagnet

    Directory of Open Access Journals (Sweden)

    V.V. Kulish

    2015-06-01

    Full Text Available The paper investigates the antiferromagnetic vector distribution in an antiferromagnetic film with a system of antidots. A static distribution of the antiferromagnetic vector is written and a method – based on the minimization of the antiferromagnet energy – that allows reducing the number of boundary conditions required for finding the constants of this distribution is proposed. Equations for the distribution constants are obtained for the both cases of minimizing the antiferromagnet energy by one and by two distribution constants that enter the expression for the antiferromagnet energy. The method is illustrated on a system of one isolated antidot. For such system, one additional condition – for the case when two boundary conditions on the surface of the antidot are given – and two additional conditions – for the case when one boundary condition on the surface of the antidot is given – on the distribution constants are written.

  19. Switching of antiferromagnetic chains with magnetic pulses

    Science.gov (United States)

    Tao, Kun; Polyakov, Oleg P.; Stepanyuk, Valeri S.

    2016-04-01

    Recent experimental studies have demonstrated the possibility of information storage in short antiferromagnetic chains on an insulator substrate [S. Loth et al., Science 335, 196 (2012), 10.1126/science.1214131]. Here, using the density functional theory and atomistic spin dynamics simulations, we show that a local magnetic control of such chains with a magnetic tip and magnetic pulses can be used for fast switching of their magnetization. Furthermore, by changing the position of the tip one can engineer the magnetization dynamics of the chains.

  20. Classical and quantum anisotropic Heisenberg antiferromagnets

    Directory of Open Access Journals (Sweden)

    W. Selke

    2009-01-01

    Full Text Available We study classical and quantum Heisenberg antiferromagnets with exchange anisotropy of XXZ-type and crystal field single-ion terms of quadratic and quartic form in a field. The magnets display a variety of phases, including the spin-flop (or, in the quantum case, spin-liquid and biconical (corresponding, in the quantum lattice gas description, to supersolid phases. Applying ground-state considerations, Monte Carlo and density matrix renormalization group methods, the impact of quantum effects and lattice dimension is analysed. Interesting critical and multicritical behaviour may occur at quantum and thermal phase transitions.

  1. Frustrated 3×3 Heisenberg antiferromagnets

    Science.gov (United States)

    Moustanis, P. N.

    2016-08-01

    The full energy spectrum and the exact thermodynamic results of the antiferromagnetic Heisenberg Hamiltonian of the 3×3 triangular and the frustrated square lattice with periodic boundary conditions and s=1/2 are obtained. To this end the method of hierarchy of algebras is employed. It was found that the ground state of the 3×3 frustrated square lattice is a Resonating Valence Bond (RVB) state. Thermodynamic properties, like the specific heat, magnetic susceptibility, the thermal average of the square of the total Sz and entropy, for these two lattices are presented.

  2. Antiferromagnetic noise correlations in optical lattices

    DEFF Research Database (Denmark)

    Bruun, Niels Bohr International Academy, University of Copenhagen, DK-2100 Copenhagen Ø, Denmark, Georg Morten; Syljuåsen, F. T.; Pedersen, K. G. L.;

    2009-01-01

    We analyze how noise correlations probed by time-of-flight experiments reveal antiferromagnetic (AF) correlations of fermionic atoms in two-dimensional and three-dimensional optical lattices. Combining analytical and quantum Monte Carlo calculations using experimentally realistic parameters, we...... show that AF correlations can be detected for temperatures above and below the critical temperature for AF ordering. It is demonstrated that spin-resolved noise correlations yield important information about the spin ordering. Finally, we show how to extract the spin correlation length and the related...

  3. High-Tc spin superfluidity in antiferromagnets.

    Science.gov (United States)

    Bunkov, Yu M; Alakshin, E M; Gazizulin, R R; Klochkov, A V; Kuzmin, V V; L'vov, V S; Tagirov, M S

    2012-04-27

    We report the observation of the unusual behavior of induction decay signals in antiferromagnetic monocrystals with Suhl-Nakamura interactions. The signals show the formation of the Bose-Einstein condensation (BEC) of magnons and the existence of spin supercurrent, in complete analogy with the spin superfluidity in the superfluid (3)He and the atomic BEC of quantum gases. In the experiments described here, the temperature of the magnon BEC is a thousand times larger than in the superfluid (3)He. It opens a possibility to apply the spin supercurrent for various magnetic spintronics applications.

  4. Lattice distortion in disordered antiferromagnetic XY models

    Institute of Scientific and Technical Information of China (English)

    Li Peng-Fei; Cao Hai-Jing

    2012-01-01

    The behavior of lattice distortion in spin 1/2 antiferromagnetic XY models with random magnetic modulation is investigated with the consideration of spin-phonon coupling in the adiabatic limit.It is found that lattice distortion relies on the strength of the random modulation.For strong or weak enough spin-phonon couplings,the average lattice distortion may decrease or increase as the random modulation is strengthened.This may be the result of competition between the random magnetic modulation and the spin-phonon coupling.

  5. Antiferromagnetic phase diagram of the cuprate superconductors

    Science.gov (United States)

    Nunes, L. H. C. M.; Teixeira, A. W.; Marino, E. C.

    2017-02-01

    Taking the spin-fermion model as the starting point for describing the cuprate superconductors, we obtain an effective nonlinear sigma-field hamiltonian, which takes into account the effect of doping in the system. We obtain an expression for the spin-wave velocity as a function of the chemical potential. For appropriate values of the parameters we determine the antiferromagnetic phase diagram for the YBa2Cu3O6+x compound as a function of the dopant concentration in good agreement with the experimental data. Furthermore, our approach provides a unified description for the phase diagrams of the hole-doped and the electron doped compounds, which is consistent with the remarkable similarity between the phase diagrams of these compounds, since we have obtained the suppression of the antiferromagnetic phase as the modulus of the chemical potential increases. The aforementioned result then follows by considering positive values of the chemical potential related to the addition of holes to the system, while negative values correspond to the addition of electrons.

  6. Topological gapless phases in nonsymmorphic antiferromagnets

    Science.gov (United States)

    Brzezicki, Wojciech; Cuoco, Mario

    2017-04-01

    We investigate the nature of the electronic states in a variety of nonsymmorphic collinear antiferromagnets with glide reflection symmetry, a combination of mirror and half-lattice translation. In particular, the study refers to a class of systems with two-band itinerant electrons that are spin-orbit coupled and interacting with a magnetic background having a zigzag pattern. We describe the symmetry properties of the model system by focusing on the role of nonsymmorphic transformations arising from the antiferromagnetic structure of the spin ordering. Gapless phases with Dirac points having different types of symmetry-protection as well as electronic structures with triple and quadruple band-crossing points are obtained. A glide semimetal is shown to be converted into a gapless phase with Dirac points protected by inversion and time-inversion symmetry combination. Interestingly, we find a relation between the states in the glide sectors that provides a general mechanism to get multiple band touching points. The split of the multiple Fermi points drives the transition from a point node to a line node semimetal or to a metal with nontrivial winding around the Fermi pockets and an electronic structure that is tied to the presence of glide symmetric Dirac points. Besides a new perspective of ordered states in complex materials, our findings indicate relevant paths to topological gapless phases and edge states in a wide class of magnetic systems.

  7. Charge Stripes and Antiferromagnetism in Copper-Oxide Superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Tranquada, J.M.

    1997-12-31

    Superconducting cuprate compounds are obtained by doping holes into antiferromagnetic insulators. Neutron scattering studies have provided evidence that the doped holes tend to segregate into charge stripes, which act like domain walls between antiferromagnetic regions. The interaction between the spatially segregated holes and the magnetic domains may be responsible for the strong pairing interaction found in the cuprates.

  8. Tailoring exchange couplings in magnetic topological-insulator/antiferromagnet heterostructures

    Science.gov (United States)

    He, Qing Lin; Kou, Xufeng; Grutter, Alexander J.; Yin, Gen; Pan, Lei; Che, Xiaoyu; Liu, Yuxiang; Nie, Tianxiao; Zhang, Bin; Disseler, Steven M.; Kirby, Brian J.; Ratcliff, William, II; Shao, Qiming; Murata, Koichi; Zhu, Xiaodan; Yu, Guoqiang; Fan, Yabin; Montazeri, Mohammad; Han, Xiaodong; Borchers, Julie A.; Wang, Kang L.

    2017-01-01

    Magnetic topological insulators such as Cr-doped (Bi,Sb)2Te3 provide a platform for the realization of versatile time-reversal symmetry-breaking physics. By constructing heterostructures exhibiting Néel order in an antiferromagnetic CrSb and ferromagnetic order in Cr-doped (Bi,Sb)2Te3, we realize emergent interfacial magnetic phenomena which can be tailored through artificial structural engineering. Through deliberate geometrical design of heterostructures and superlattices, we demonstrate the use of antiferromagnetic exchange coupling in manipulating the magnetic properties of magnetic topological insulators. Proximity effects are shown to induce an interfacial spin texture modulation and establish an effective long-range exchange coupling mediated by antiferromagnetism, which significantly enhances the magnetic ordering temperature in the superlattice. This work provides a new framework on integrating topological insulators with antiferromagnetic materials and unveils new avenues towards dissipationless topological antiferromagnetic spintronics.

  9. Superconductivity, Antiferromagnetism, and Kinetic Correlation in Strongly Correlated Electron Systems

    Directory of Open Access Journals (Sweden)

    Takashi Yanagisawa

    2015-01-01

    Full Text Available We investigate the ground state of two-dimensional Hubbard model on the basis of the variational Monte Carlo method. We use wave functions that include kinetic correlation and doublon-holon correlation beyond the Gutzwiller ansatz. It is still not clear whether the Hubbard model accounts for high-temperature superconductivity. The antiferromagnetic correlation plays a key role in the study of pairing mechanism because the superconductive phase exists usually close to the antiferromagnetic phase. We investigate the stability of the antiferromagnetic state when holes are doped as a function of the Coulomb repulsion U. We show that the antiferromagnetic correlation is suppressed as U is increased exceeding the bandwidth. High-temperature superconductivity is possible in this region with enhanced antiferromagnetic spin fluctuation and pairing interaction.

  10. Ferroelectric strain modulation of antiferromagnetic moments in Ni/NiO ferromagnet/antiferromagnet heterostructures

    Science.gov (United States)

    Zhang, Yu-Jun; Chen, Jia-Hui; Li, Liang-Liang; Ma, Jing; Nan, Ce-Wen; Lin, Yuan-Hua

    2017-05-01

    Electric field manipulation of magnetic properties has attracted a lot of research interest recently in solid-state physics. However, ferroelectric strain modulation of antiferromagnetic (AFM) layer is rarely studied in ferromagnet/antiferromagnet/ferroelectric heterostructures. In this paper, we prepared a Ni/NiO(001) heterostructure on ferroelectric Pb (Mg1/3N b2 /3 ) 0.7T i0.3O3(001 ) substrates and observed an out-of-plane electric field modulation of exchange bias and magnetic anisotropy in the Ni layer. The exchange bias was easily eliminated by an electric field cycle, which was due to the AFM domain switching induced by piezoelectric strain in the NiO layer. Synchrotron x ray linear dichroism results confirmed the AFM moment alignment induced by ferroelectric strain as well. Our work showed a promising strategy to manipulate AFM moments and domains, serving the blooming AFM spintronics.

  11. Fractal dimension in percolating Heisenberg antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, S. [Neutron Science Laboratory, High Energy Accelerator Research Organization, Tsukuba 305-0810 (Japan)]. E-mail: shinichi.itoh@kek.jp; Kajimoto, R. [Quantum Beam Science Directorate, Japan Atomic Energy Agency, Tokai 319-1195 (Japan); Adams, M.A. [ISIS Facility, Rutherford Appleton Laboratory, Didcot, Oxon OX11 0QX (United Kingdom); Bull, M.J. [ISIS Facility, Rutherford Appleton Laboratory, Didcot, Oxon OX11 0QX (United Kingdom); Iwasa, K. [Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Aso, N. [Neutron Science Laboratory, Institute for Solid State Physics, University of Tokyo, Tokai 319-1106 (Japan); Yoshizawa, H. [Neutron Science Laboratory, Institute for Solid State Physics, University of Tokyo, Tokai 319-1106 (Japan); Takeuchi, T. [Low Temperature Center, Osaka University, Toyonaka 560-0043 (Japan)

    2007-03-15

    We investigated static and dynamical properties in the three-dimensional percolating Heisenberg antiferromagnets, RbMn{sub c}Mg{sub 1-c}F{sub 3}, with the magnetic concentration close to the percolation threshold, c{sub P}=0.312, around the superlattice point well below T{sub N}. In neutron diffraction experiment, the wave number dependence of the elastic scattering component was well fitted to q{sup -x}. Magnetic fractons were also studied using inelastic neutron scattering, and the observed fractons showed the dispersion relation of q{sup z}. The determined exponents, x=2.43+/-0.05 and z=2.5+/-0.1, were in good agreement with the fractal dimension (D{sub f}=2.48)

  12. Landau model for the multiferroic delafossite antiferromagnets

    Science.gov (United States)

    Ribeiro, J. L.; Perez-Mato, J. M.; Vieira, L. G.

    2016-10-01

    A symmetry based framework is used to describe the complex phase diagrams observed in the multiferroic delafossite compounds. A free energy Landau functional is derived from the analysis of the transformation properties of the most general incommensurate magnetic spin order parameter. A principle of maximal symmetry is invoked and the stability of each of the different higher symmetry phases considered. The competition between different potential ground states is analysed within the scope of a simplified model, which emphasizes the role of the symmetry allowed phase dependent biquadratic couplings. The cross-over between the different competing states is also discussed. The results show that the diverse set of phase diagrams that are experimentally observed in this class of triangular lattice antiferromagnets and, in particular, the stabilization of magnetically induced ferroelectric states, can be well interpreted and described within this integrated phenomenological approximation.

  13. Transformation of spin current by antiferromagnetic insulators

    Science.gov (United States)

    Khymyn, Roman; Lisenkov, Ivan; Tiberkevich, Vasil S.; Slavin, Andrei N.; Ivanov, Boris A.

    2016-06-01

    It is demonstrated theoretically that a thin layer of an anisotropic antiferromagnetic (AFM) insulator can effectively conduct spin current through the excitation of a pair of evanescent AFM spin wave modes. The spin current flowing through the AFM is not conserved due to the interaction between the excited AFM modes and the AFM lattice and, depending on the excitation conditions, can be either attenuated or enhanced. When the phase difference between the excited evanescent modes is close to π /2 , there is an optimum AFM thickness for which the output spin current reaches a maximum, which can significantly exceed the magnitude of the input spin current. The spin current transfer through the AFM depends on the ambient temperature and increases substantially when temperature approaches the Néel temperature of the AFM layer.

  14. Magnetic Properties of Nanoparticles of Antiferromagnetic Materials

    DEFF Research Database (Denmark)

    Mørup, Steen; Frandsen, Cathrine; Bødker, Franz

    2003-01-01

    The magnetic properties of antiferromagnetic nanoparticles have been studied by Mossbauer spectroscopy and neutron scattering. Temperature series of Mossbauer spectra of non-interacting, superparamagnetic hematite nanoparticles were fitted by use of the Blume-Tjon relaxation model. It has been...... found that the magnetic anisotropy energy constant increases significantly with decreasing particle size. Neutron scattering experiments on similar samples give new information on both superparamagnetic relaxation and collective magnetic excitations. There is good agreement between the values...... of the parameters obtained from Mossbauer spectroscopy and neutron scattering. In samples of interacting hematite nanoparticles, the relaxation was significantly suppressed. The Mossbauer data for these samples are in accordance with a mean field model for an ordered state of strongly interacting particles. Mixing...

  15. Antiferromagnetic spin wave and the superconductivity

    Science.gov (United States)

    Koh, Shun-ichiro

    2000-07-01

    The neutron scattering of UPd 2Al 3 showed that a sharp peak, which is absent in the normal phase, appears in the superconducting phase (Metoki et al., J. Phys. Soc. Japan 66 (1997) 2560; Bernhoeft et al., Phys. Rev. Lett. 81 (1998) 4244). Assuming this excitation to be an antiferromagnetic (AFM) spin-wave, this paper deals with its enhancement by the superconductivity. Applying the slave-boson formalism, we consider the AFM ordering as a spin-density-wave (Koh, Phys. Lett. A 253 (1999) 98). Above Tc, the spin-wave suffers an energy dissipation due to the conduction electron. Below Tc, the superconductivity suppresses the dissipation, resulting in the growth of the AFM spin-wave.

  16. Spin dynamics in geometrically frustrated antiferromagnetic pyrochlores

    Science.gov (United States)

    Gardner, J. S.; Ehlers, G.; Bramwell, S. T.; Gaulin, B. D.

    2004-03-01

    We have studied the spin dynamics of several antiferromagnetic pyrochlore oxides. These magnets are geometrically frustrated and only reach their ground states at temperatures much lower than that expected from mean field theory. Here we present data on the magnetic nature, especially the spin dynamics of Tb2Ti2O7, Gd2Ti2O7 and Y2Mo2O7. In these systems the ground states are found to be very different. Y2Mo2O7 freezes completely into a spin glass-like state, Tb2Ti2O7 is a cooperative paramagnetic and remains dynamic down to 15 mK and Gd2Ti2O7 enters a unique partially ordered state at {\\sim }1 K.

  17. Probing the evolution of antiferromagnetism in multiferroics

    Energy Technology Data Exchange (ETDEWEB)

    Holcomb, M.; Martin, L.; Scholl, A.; He, Q.; Yu, P.; Yang, C.-H.; Yang, S.; Glans, P.-A.; Valvidares, M.; Huijben, M.; Kortright, J.; Guo,, J.; Chu, Y.-H.; Ramesh, R.

    2010-06-09

    This study delineates the evolution of magnetic order in epitaxial films of the room-temperature multiferroic BiFeO3 system. Using angle- and temperature-dependent dichroic measurements and spectromicroscopy, we have observed that the antiferromagnetic order in the model multiferroic BiFeO3 evolves systematically as a function of thickness and strain. Lattice-mismatch-induced strain is found to break the easy-plane magnetic symmetry of the bulk and leads to an easy axis of magnetization which can be controlled through strain. Understanding the evolution of magnetic structure and how to manipulate the magnetism in this model multiferroic has significant implications for utilization of such magnetoelectric materials in future applications.

  18. Quasiparticle bandstructure of antiferromagnetic EuTe

    Science.gov (United States)

    Mathi Jaya, S.; Nolting, W.

    1997-11-01

    The temperature-dependent electronic quasiparticle spectrum of the antiferromagnetic semiconductor EuTe is derived by use of a combination of a many-body model procedure with a tight-binding - `linear muffin tin orbital' (TB - LMTO) band structure calculation. The central part is the d - f model for a single band electron (`test electron') being exchange coupled to the antiferromagnetically ordered localized moments of the Eu ions. The single-electron Bloch energies of the d - f model are taken from a TB - LMTO calculation for paramagnetic EuTe. The d - f model is evaluated by a recently proposed moment conserving Green function technique to get the temperature-dependent sublattice - quasiparticle bandstructure (S - QBS) and sublattice - quasiparticle density of states (S - QDOS) of the unoccupied 5d - 6s energy bands. Unconventional correlation effects and the appearance of characteristic quasiparticles (`magnetic polarons') are worked out in detail. The temperature dependence of the S - QDOS and S - QBS is mainly provoked by the spectral weights of the energy dispersions. Minority- and majority-spin spectra coincide for all temperatures but with different densities of states. Upon cooling from 0953-8984/9/47/012/img1 to T = 0 K the lower conduction band edge exhibits a small blue shift of -0.025 eV in accordance with the experiment. Quasiparticle damping manifesting itself in a temperature-dependent broadening of the spectral density peaks arises from spin exchange processes between (5d - 6s) conduction band electrons and localized 4f moments.

  19. Computational design of a robust two-dimensional antiferromagnetic semiconductor

    Science.gov (United States)

    Chabungbam, Satyananda; Sen, Prasenjit

    2017-07-01

    Using density functional theory calculations, we establish the hitherto unknown compound CrCTe3 to be a stable antiferromagnetic semiconductor in the R 3 ¯ crystal structure with an indirect fundamental gap. Successive layers in the bulk compound are weakly bound by van der Waals forces so that individual layers can be easily exfoliated. A monolayer of CrCTe3 is also an antiferromagnetic semiconductor. The monolayer is structurally stable over a large range of compressive and tensile strains, and the antiferromagnetic state is robust over this strain range. Band gap of the monolayer can be tuned by as much as 50% by applying strain in this range.

  20. Magnonic analog of relativistic Zitterbewegung in an antiferromagnetic spin chain

    Science.gov (United States)

    Wang, Weiwei; Gu, Chenjie; Zhou, Yan; Fangohr, Hans

    2017-07-01

    We theoretically investigate the spin-wave (magnon) excitations in a classical antiferromagnetic spin chain with easy-axis anisotropy. We obtain a Dirac-like equation by linearizing the Landau-Lifshitz-Gilbert equation in this antiferromagnetic system, in contrast to the ferromagnetic system in which a Schrödinger-type equation is derived. The Hamiltonian operator in the Dirac-like equation is a pseudo-Hermitian. We compute and demonstrate relativistic Zitterbewegung (trembling motion) in the antiferromagnetic spin chain by measuring the expectation values of the wave-packet position.

  1. Long-range interactions in antiferromagnetic quantum spin chains

    Science.gov (United States)

    Bravo, B.; Cabra, D. C.; Gómez Albarracín, F. A.; Rossini, G. L.

    2017-08-01

    We study the role of long-range dipolar interactions on antiferromagnetic spin chains, from the classical S →∞ limit to the deep quantum case S =1 /2 , including a transverse magnetic field. To this end, we combine different techniques such as classical energy minima, classical Monte Carlo, linear spin waves, bosonization, and density matrix renormalization group (DMRG). We find a phase transition from the already reported dipolar ferromagnetic region to an antiferromagnetic region for high enough antiferromagnetic exchange. Thermal and quantum fluctuations destabilize the classical order before reaching magnetic saturation in both phases, and also close to zero field in the antiferromagnetic phase. In the extreme quantum limit S =1 /2 , extensive DMRG computations show that the main phases remain present with transition lines to saturation significatively shifted to lower fields, in agreement with the bosonization analysis. The overall picture maintains a close analogy with the phase diagram of the anisotropic XXZ spin chain in a transverse field.

  2. Experimental and theoretical studies of nanoparticles of antiferromagnetic materials

    DEFF Research Database (Denmark)

    Mørup, Steen; Madsen, Daniel Esmarch; Frandsen, Cathrine;

    2007-01-01

    The magnetic properties of nanoparticles of antiferromagnetic materials are reviewed. The magnetic structure is often similar to the bulk structure, but there are several examples of size-dependent magnetic structures. Owing to the small magnetic moments of antiferromagnetic nanoparticles...... measurements, Mössbauer spectroscopy and neutron scattering. Below the blocking temperature, the magnetic dynamics in nanoparticles is dominated by thermal excitations of the uniform mode. In antiferromagnetic nanoparticles, the frequency of this mode is much higher than in ferromagnetic and ferrimagnetic...... nanoparticles, but it depends crucially on the size of the uncompensated moment. Excitation of the uniform mode results in a so-called thermoinduced moment, because the two sublattices are not strictly antiparallel when this mode is excited. The magnetic dipole interaction between antiferromagnetic...

  3. Quasi-two-dimensional electron gas at the epitaxial alumina/SrTiO{sub 3} interface: Control of oxygen vacancies

    Energy Technology Data Exchange (ETDEWEB)

    Kormondy, Kristy J.; Posadas, Agham B.; Demkov, Alexander A., E-mail: demkov@physics.utexas.edu [Department of Physics, University of Texas at Austin, Austin, Texas 78712 (United States); Ngo, Thong Q.; Ekerdt, John G. [Department of Chemical Engineering, University of Texas at Austin, Austin, Texas 78712 (United States); Lu, Sirong; Smith, David J.; McCartney, Martha R. [Department of Physics, Arizona State University, Tempe, Arizona 85287 (United States); Goble, Nicholas; Gao, Xuan P. A. [Department of Physics, Case Western Reserve University, Cleveland, Ohio 44106 (United States); Jordan-Sweet, Jean [IBM T.J. Watson Research Center, Yorktown Heights, New York 10598 (United States)

    2015-03-07

    In this paper, we report on the highly conductive layer formed at the crystalline γ-alumina/SrTiO{sub 3} interface, which is attributed to oxygen vacancies. We describe the structure of thin γ-alumina layers deposited by molecular beam epitaxy on SrTiO{sub 3} (001) at growth temperatures in the range of 400–800 °C, as determined by reflection-high-energy electron diffraction, x-ray diffraction, and high-resolution electron microscopy. In situ x-ray photoelectron spectroscopy was used to confirm the presence of the oxygen-deficient layer. Electrical characterization indicates sheet carrier densities of ∼10{sup 13 }cm{sup −2} at room temperature for the sample deposited at 700 °C, with a maximum electron Hall mobility of 3100 cm{sup 2}V{sup −1}s{sup −1} at 3.2 K and room temperature mobility of 22 cm{sup 2}V{sup −1}s{sup −1}. Annealing in oxygen is found to reduce the carrier density and turn a conductive sample into an insulator.

  4. Coherent optical nonlinearities and phase relaxation of quasi-three-dimensional and quasi-two-dimensional excitons in ZnSxSe1 - x/ZnSe structures

    DEFF Research Database (Denmark)

    Wagner, Hans Peter; Schätz, A.; Maier, R.

    1997-01-01

    We investigate the dephasing of heavy-hole excitons in different free-standing ZnSxSe1-x/ZnSe layer structures by spectrally resolved transient four-wave mixing. ZnSe layers of 80, 8, and 4 nm thickness with ternary barriers are studied, representing the crossover from quasi-three-dimensional to ......We investigate the dephasing of heavy-hole excitons in different free-standing ZnSxSe1-x/ZnSe layer structures by spectrally resolved transient four-wave mixing. ZnSe layers of 80, 8, and 4 nm thickness with ternary barriers are studied, representing the crossover from quasi...

  5. Transport properties of a quasi-two-dimensional electron system formed in LaAlO3/EuTiO3/SrTiO3 heterostructures

    Science.gov (United States)

    De Luca, G. M.; Di Capua, R.; Di Gennaro, E.; Granozio, F. Miletto; Stornaiuolo, D.; Salluzzo, M.; Gadaleta, A.; Pallecchi, I.; Marrè, D.; Piamonteze, C.; Radovic, M.; Ristic, Z.; Rusponi, S.

    2014-06-01

    We study the structural, magnetic, and transport properties of LaAlO3/EuTiO3/SrTiO3 heterostructures grown by pulsed laser deposition. The samples are characterized in situ by electron diffraction and scanning probe microscopy and ex situ by transport measurements and x-ray absorption spectroscopy. LaAlO3/EuTiO3/SrTiO3 films show a ferromagnetic transition at T ≤7.5 K, related to the ordering of Eu2+ spins, even in samples characterized by just two EuTiO3 unit cells. A finite metallic conductivity is observed only in the case of samples composed by one or two EuTiO3 unit cells and, simultaneously, by a LaAlO3 thickness greater than or equal to four unit cells. The effect of ferromagnetic EuTiO3 on the transport properties of δ-doped LaAlO3/EuTiO3/SrTiO3 is critically discussed.

  6. Flexible Quasi-Two-Dimensional CoFe2O4 Epitaxial Thin Films for Continuous Strain Tuning of Magnetic Properties.

    Science.gov (United States)

    Zhang, Yong; Shen, Lvkang; Liu, Ming; Li, Xin; Lu, Xiaoli; Lu, Lu; Ma, Chunrui; You, Caiyin; Chen, Aiping; Huang, Chuanwei; Chen, Lang; Alexe, Marin; Jia, Chun-Lin

    2017-08-22

    Epitaxial thin films of CoFe2O4 (CFO) have successfully been transferred from a SrTiO3 substrate onto a flexible polyimide substrate. By bending the flexible polyimide, different levels of uniaxial strain are continuously introduced into the CFO epitaxial thin films. Unlike traditional epitaxial strain induced by substrates, the strain from bending will not suffer from critical thickness limitation, crystalline quality variation, and substrate clamping, and more importantly, it provides a more intrinsic and reliable way to study strain-controlled behaviors in functional oxide systems. It is found that both the saturation magnetization and coercivity of the transferred films can be changed over the bending status and show a high accord with the movement of the curvature bending radius of the polyimide substrate. This reveals that the mechanical strain plays a critical role in tuning the magnetic properties of CFO thin films parallel and perpendicular to the film plane direction.

  7. Characterization of the Dilute Ising Antiferromagnet

    Energy Technology Data Exchange (ETDEWEB)

    Wiener, T.

    2000-09-12

    A spin glass is a magnetic ground state in which ferromagnetic and antiferromagnetic exchange interactions compete, thereby creating frustration and a multidegenerate state with no long range order. An Ising system is a system where the spins are constrained to lie parallel or antiparallel to a primary axis. There has been much theoretical interest in the past ten years in the effects of applying a magnetic field transverse to the primary axis in an Ising spin glass at low temperatures and thus study phase transitions at the T=0 limit. The focus of this study is to search for and characterize a new Ising spin glass system. This is accomplished by site diluting yttrium for terbium in the crystalline material TbNi{sub 2}Ge{sub 2}. The first part of this work gives a brief overview of the physics of rare earth magnetism and an overview of experimental characteristics of spin glasses. This is followed by the methodology used to manufacture the large single crystals used in this study, as well as the measurement techniques used. Next, a summary of the results of magnetic measurements on across the dilution series from pure terbium to pure yttrium is presented. This is followed by detailed measurements on particular dilutions which demonstrate spin glass behavior. Pure TbNi{sub 2}Ge{sub 2} is an Ising antiferromagnet with a several distinct metamagnetic states below 17 K. As the terbium is alloyed with yttrium, these magnetic states are weakened in a consistent manner, as is seen in measurements of the transition temperatures and analysis of Curie-Weiss behavior at high temperature. At low concentrations of terbium, below 35%, long range order is no longer present and a spin-glass-like state emerges. This state is studied through various measurements, dc and ac susceptibility, resistivity, and specific heat. This magnetic behavior was then compared to that of other well characterized spin glasses. It is concluded that there is a region of concentration s for which a spin

  8. Characterization of the Dilute Ising Antiferromagnet

    Energy Technology Data Exchange (ETDEWEB)

    Wiener, Timothy [Iowa State Univ., Ames, IA (United States)

    2000-09-12

    A spin glass is a magnetic ground state in which ferromagnetic and antiferromagnetic exchange interactions compete, thereby creating frustration and a multidegenerate state with no long range order. An Ising system is a system where the spins are constrained to lie parallel or antiparallel to a primary axis. There has been much theoretical interest in the past ten years in the effects of applying a magnetic field transverse to the primary axis in an Ising spin glass at low temperatures and thus study phase transitions at the T=0 limit. The focus of this study is to search for and characterize a new Ising spin glass system. This is accomplished by site diluting yttrium for terbium in the crystalline material TbNi2Ge2. The first part of this work gives a brief overview of the physics of rare earth magnetism and an overview of experimental characteristics of spin glasses. This is followed by the methodology used to manufacture the large single crystals used in this study, as well as the measurement techniques used. Next, a summary of the results of magnetic measurements on across the dilution series from pure terbium to pure yttrium is presented. This is followed by detailed measurements on particular dilutions which demonstrate spin glass behavior. Pure TbNi2Ge2 is an Ising antiferromagnet with a several distinct metamagnetic states below 17 K. As the terbium is alloyed with yttrium, these magnetic states are weakened in a consistent manner, as is seen in measurements of the transition temperatures and analysis of Curie-Weiss behavior at high temperature. At low concentrations of terbium, below 35%, long range order is no longer present and a spin-glass-like state emerges. This state is studied through various measurements, dc and ac susceptibility, resistivity, and specific heat. This magnetic behavior was then compared to that of other well characterized spin glasses. It is concluded that there is a region of

  9. Reversal of exchange bias in nanocrystalline antiferromagnetic-ferromagnetic bilayers

    CERN Document Server

    Prados, C; Hernando, A; Montone, A

    2002-01-01

    The sign of the exchange bias in field cooled nanocrystalline antiferromagnetic-ferromagnetic bilayers (Co-O and Ni-O/permalloy) is reversed at temperatures approaching the antiferromagnetic (AFM) blocking temperature. A similar phenomenon is observed after magnetic training processes at similar temperatures. These effects can be explained assuming that the boundaries of nanocrystalline grains in AFM layers exhibit lower transition temperatures than grain cores.

  10. Thermally activated repolarization of antiferromagnetic particles: Monte Carlo dynamics

    Science.gov (United States)

    Soloviev, S. V.; Popkov, A. F.; Knizhnik, A. A.; Iskandarova, I. M.

    2017-02-01

    Based on the equation of motion of an antiferromagnetic moment, taking into account a random field of thermal fluctuations, we propose a Monte Carlo (MC) scheme for the numerical simulation of the evolutionary dynamics of an antiferromagnetic particle, corresponding to the Langevin dynamics in the Kramers theory for the two-well potential. Conditions for the selection of the sphere of fluctuations of random deviations of the antiferromagnetic vector at an MC time step are found. A good agreement with the theory of Kramers thermal relaxation is demonstrated for varying temperatures and heights of energy barrier over a wide range of integration time steps in an overdamped regime. Based on the developed scheme, we performed illustrative calculations of the temperature drift of the exchange bias under the fast annealing of a ferromagnet-antiferromagnet structure, taking into account the random variation of anisotropy directions in antiferromagnetic grains and their sizes. The proposed approach offers promise for modeling magnetic sensors and spintronic memory devices containing heterostructures with antiferromagnetic layers.

  11. Nonequilibrium antiferromagnetic mixed-spin Ising model.

    Science.gov (United States)

    Godoy, Mauricio; Figueiredo, Wagner

    2002-09-01

    We studied an antiferromagnetic mixed-spin Ising model on the square lattice subject to two competing stochastic processes. The model system consists of two interpenetrating sublattices of spins sigma=1/2 and S=1, and we take only nearest neighbor interactions between pairs of spins. The system is in contact with a heat bath at temperature T, and the exchange of energy with the heat bath occurs via one-spin flip (Glauber dynamics). Besides, the system interacts with an external agency of energy, which supplies energy to it whenever two nearest neighboring spins are simultaneously flipped. By employing Monte Carlo simulations and a dynamical pair approximation, we found the phase diagram for the stationary states of the model in the plane temperature T versus the competition parameter between one- and two-spin flips p. We observed the appearance of three distinct phases, that are separated by continuous transition lines. We also determined the static critical exponents along these lines and we showed that this nonequilibrium model belongs to the universality class of the two-dimensional equilibrium Ising model.

  12. Robust ferromagnetism carried by antiferromagnetic domain walls

    Science.gov (United States)

    Hirose, Hishiro T.; Yamaura, Jun-Ichi; Hiroi, Zenji

    2017-02-01

    Ferroic materials, such as ferromagnetic or ferroelectric materials, have been utilized as recording media for memory devices. A recent trend for downsizing, however, requires an alternative, because ferroic orders tend to become unstable for miniaturization. The domain wall nanoelectronics is a new developing direction for next-generation devices, in which atomic domain walls, rather than conventional, large domains themselves, are the active elements. Here we show that atomically thin magnetic domain walls generated in the antiferromagnetic insulator Cd2Os2O7 carry unusual ferromagnetic moments perpendicular to the wall as well as electron conductivity: the ferromagnetic moments are easily polarized even by a tiny field of 1 mT at high temperature, while, once cooled down, they are surprisingly robust even in an inverse magnetic field of 7 T. Thus, the magnetic domain walls could serve as a new-type of microscopic, switchable and electrically readable magnetic medium which is potentially important for future applications in the domain wall nanoelectronics.

  13. Antiferromagnetic Skyrmion: Stability, Creation and Manipulation

    Science.gov (United States)

    Zhang, Xichao; Zhou, Yan; Ezawa, Motohiko

    2016-04-01

    Magnetic skyrmions are particle-like topological excitations in ferromagnets, which have the topo-logical number Q = ± 1, and hence show the skyrmion Hall effect (SkHE) due to the Magnus force effect originating from the topology. Here, we propose the counterpart of the magnetic skyrmion in the antiferromagnetic (AFM) system, that is, the AFM skyrmion, which is topologically protected but without showing the SkHE. Two approaches for creating the AFM skyrmion have been described based on micromagnetic lattice simulations: (i) by injecting a vertical spin-polarized current to a nanodisk with the AFM ground state; (ii) by converting an AFM domain-wall pair in a nanowire junction. It is demonstrated that the AFM skyrmion, driven by the spin-polarized current, can move straightly over long distance, benefiting from the absence of the SkHE. Our results will open a new strategy on designing the novel spintronic devices based on AFM materials.

  14. Room-temperature antiferromagnetic memory resistor.

    Science.gov (United States)

    Marti, X; Fina, I; Frontera, C; Liu, Jian; Wadley, P; He, Q; Paull, R J; Clarkson, J D; Kudrnovský, J; Turek, I; Kuneš, J; Yi, D; Chu, J-H; Nelson, C T; You, L; Arenholz, E; Salahuddin, S; Fontcuberta, J; Jungwirth, T; Ramesh, R

    2014-04-01

    The bistability of ordered spin states in ferromagnets provides the basis for magnetic memory functionality. The latest generation of magnetic random access memories rely on an efficient approach in which magnetic fields are replaced by electrical means for writing and reading the information in ferromagnets. This concept may eventually reduce the sensitivity of ferromagnets to magnetic field perturbations to being a weakness for data retention and the ferromagnetic stray fields to an obstacle for high-density memory integration. Here we report a room-temperature bistable antiferromagnetic (AFM) memory that produces negligible stray fields and is insensitive to strong magnetic fields. We use a resistor made of a FeRh AFM, which orders ferromagnetically roughly 100 K above room temperature, and therefore allows us to set different collective directions for the Fe moments by applied magnetic field. On cooling to room temperature, AFM order sets in with the direction of the AFM moments predetermined by the field and moment direction in the high-temperature ferromagnetic state. For electrical reading, we use an AFM analogue of the anisotropic magnetoresistance. Our microscopic theory modelling confirms that this archetypical spintronic effect, discovered more than 150 years ago in ferromagnets, is also present in AFMs. Our work demonstrates the feasibility of fabricating room-temperature spintronic memories with AFMs, which in turn expands the base of available magnetic materials for devices with properties that cannot be achieved with ferromagnets.

  15. Landau model for the multiferroic delafossite antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Ribeiro, J.L, E-mail: jlr@fisica.uminho.pt [Centro de Física da Universidade do Minho, 4710-057 Braga (Portugal); Perez-Mato, J.M [Dpto. de Física de la Materia Condensada, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, 48080 Bilbao (Spain); Vieira, L.G [Centro de Física da Universidade do Minho, 4710-057 Braga (Portugal)

    2016-10-15

    A symmetry based framework is used to describe the complex phase diagrams observed in the multiferroic delafossite compounds. A free energy Landau functional is derived from the analysis of the transformation properties of the most general incommensurate magnetic spin order parameter. A principle of maximal symmetry is invoked and the stability of each of the different higher symmetry phases considered. The competition between different potential ground states is analysed within the scope of a simplified model, which emphasizes the role of the symmetry allowed phase dependent biquadratic couplings. The cross-over between the different competing states is also discussed. The results show that the diverse set of phase diagrams that are experimentally observed in this class of triangular lattice antiferromagnets and, in particular, the stabilization of magnetically induced ferroelectric states, can be well interpreted and described within this integrated phenomenological approximation. - Highlights: • Symmetry considerations are used to analyze the phase diagrams of the compounds. • The competition between possible ground states is discussed. • The field induced transitions between competing states are described.

  16. Antiferromagnet-induced perpendicular magnetic anisotropy in ferromagnetic/antiferromagnetic/ferromagnetic trilayers

    Science.gov (United States)

    Wang, Bo-Yao; Lin, Po-Han; Tsai, Ming-Shian; Shih, Chun-Wei; Lee, Meng-Ju; Huang, Chun-Wei; Jih, Nae-Yeou; Wei, Der-Hsin

    2016-08-01

    This study demonstrates the effect of antiferromagnet-induced perpendicular magnetic anisotropy (PMA) on ferromagnetic/antiferromagnetic/ferromagnetic (FM/AFM/FM) trilayers and reveals its interplay with a long-range interlayer coupling between separated FM layers. In epitaxially grown 12 monolayer (ML) Ni/Co/Mn/5 ML Co/Cu(001) films, magnetic hysteresis loops and element-resolved magnetic domain imaging showed that the magnetization direction of the top layers of 12 ML Ni/Co films could be changed from the in-plane direction to the perpendicular direction, when the thickness of the Mn films (tMn) was greater than a critical value close to the thickness threshold associated with the onset of AFM ordering (tMn=3.5 ML). The top FM layers exhibited a significantly enhanced PMA when tMn increased further, and this enhancement can be attributed to a strengthened AFM ordering of the volume moments of the Mn films, as evidenced by the presence of induced domain frustration. By contrast, the long-range interlayer coupling presented clear effects only when tMn was at a lower coverage.

  17. Quasiparticle band structure of antiferromagnetic Eu Te

    Energy Technology Data Exchange (ETDEWEB)

    Mathi Jaya, S.; Nolting, W. [Humboldt-Universitaet zu Berlin, Institut fuer Physik, Lehrstuhl Festkoerpertheorie, Invalidenstrasse 110, D-10115 Berlin (Germany)

    1997-11-24

    The temperature-dependent electronic quasiparticle spectrum of the antiferromagnetic semiconductor Eu Te is derived by use of a combination of a many-body model procedure with a tight-binding-'linear muffin tin orbital' (TB - LMTO) band structure calculation. The central part is the d-f model for a single band electron ('test electron') being exchange coupled to the anti ferromagnetically ordered localized moments of the Eu ions. The single-electron Bloch energies of the d-f model are taken from a TB-LMTO calculation for paramagnetic Eu Te. The d-f model is evaluated by a recently proposed moment conserving Green function technique to get the temperature-dependent sublattice-quasiparticle band structure (S-QBS) and sublattice-quasiparticle density of states (S-QDOS) of the unoccupied 5 d-6 s energy bands. Unconventional correlation effects and the appearance of characteristic quasiparticles ('magnetic polarons') are worked out in detail. The temperature dependence of the S-QDOS and S-QBS is mainly provoked by the spectral weights of the energy dispersions. Minority- and majority-spin spectra coincide for all temperatures but with different densities of states. Upon cooling from T{sub N} to T = 0 K the lower conduction band edge exhibits a small blue shift of -0.025 eV in accordance with the experiment. Quasiparticle damping manifesting itself in a temperature-dependent broadening of the spectral density peaks arises from spin exchange processes between (5 d-6 s) conduction band electrons and localized 4 f moments. (author)

  18. COMPUTER SIMULATION OF ANTIFERROMAGNETIC STRUCTURES DESCRIBED BY THE THREE-VERTEX ANTIFERROMAGNETIC POTTS MODEL

    Directory of Open Access Journals (Sweden)

    Yarash K. Abuev

    2017-01-01

    Full Text Available Abstract. Objectives A computer simulation of the antiferromagnetic structures described by the three-vertex Potts model on a triangular lattice is performed, taking into account the antiferromagnetic exchange interactions between the nearest J1 and second J2 neighbours. The main goal of the computer simulation was to elucidate the effects of ground state and areas of frustration on the thermodynamic and magnetic properties of antiferromagnetic structures described by the lowdimensional Potts model. Method The computer simulation is based on the Monte Carlo method. This method is implemented using the Metropolis algorithm in combination with the Wolff claster algorithm. The computer simulation was carried out for low-dimensional systems with periodic boundary conditions and linear dimensions L = 24124. Results On the basis of heat capacity and entropy analysis, phase transitions were observed in the considered model to possess exchange interaction parameters J1 <0 and J2 <0 in the variation intervals 0r<0.2 and 1.0

  19. Supersymmetry protected topological phases of isostatic lattices and kagome antiferromagnets

    Science.gov (United States)

    Lawler, Michael J.

    2016-10-01

    I generalize the theory of phonon topological band structures of isostatic lattices to frustrated antiferromagnets. I achieve this with a discovery of a many-body supersymmetry (SUSY) in the phonon problem of balls and springs and its connection to local constraints satisfied by ground states. The Witten index of the SUSY model demands the Maxwell-Calladine index of mechanical structures. "Spontaneous supersymmetry breaking" is identified as the need to gap all modes in the bulk to create the topological isostatic lattice state. Since ground states of magnetic systems also satisfy local constraint conditions (such as the vanishing of the total spin on a triangle), I identify a similar SUSY structure for many common models of antiferromagnets including the square, triangluar, kagome, pyrochlore nearest-neighbor antiferromagnets, and the J2=J1/2 square-lattice antiferromagnet. Remarkably, the kagome family of antiferromagnets is the analog of topological isostatic lattices among this collection of models. Thus, a solid-state realization of the theory of phonon topological band structure may be found in frustrated magnetic materials.

  20. Magnetic and structural properties of antiferromagnetic VF{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Reuvekamp, Patrick; Kremer, Reinhard; Eger, Roland [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Nenert, Gwilherm; Hansen, Thomas [Institut Laue-Langevin, 38042 Grenoble (France)

    2013-07-01

    We report on a magnetic and structural investigation of layered antiferromagnetic system vanadium (III) fluoride. VF{sub 3} crystallizes in a distorted ReO{sub 3} structure (R anti 3c) with rotated undistorted VF{sub 6} octahedra. The V{sup +3} cations are arranged in a triangular lattice with the possibility of exhibiting magnetic frustration. Polycrystalline samples of VF{sub 3} were investigated using heat capacity, dielectric, magnetic susceptibility and neutron powder diffraction methods. Combining our results, we confirmed that VF{sub 3} undergoes long-range antiferromagnetic order at ∝19 K in accordance with literature. The antiferromagnetic order results in a magnetic structure with the magnetic moments alternating between a parallel and b parallel alignments in the ab plane. A second phase transition can be seen at ∝120 K in the heat capacity and dielectric measurements possibly associated to a minute structural distortion.

  1. Magnetic phase diagrams of classical triangular and kagome antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Gvozdikova, M V [Department of Physics, Kharkov National University, 61077 Kharkov (Ukraine); Melchy, P-E; Zhitomirsky, M E, E-mail: mike.zhitomirsky@cea.fr [Service de Physique Statistique, Magnetisme et Supraconductivite, UMR-E9001 CEA-INAC/UJF, 17 rue des Martyrs, 38054 Grenoble (France)

    2011-04-27

    We investigate the effect of geometrical frustration on the H-T phase diagrams of the classical Heisenberg antiferromagnets on triangular and kagome lattices. The phase diagrams for the two models are obtained from large-scale Monte Carlo simulations. For the kagome antiferromagnet, thermal fluctuations are unable to lift degeneracy completely and stabilize translationally disordered multipolar phases. We find a substantial difference in the temperature scales of the order by disorder effect related to different degeneracy of the low- and the high-field classical ground states in the kagome antiferromagnet. In the low-field regime, the Kosterlitz-Thouless transition into a spin-nematic phase is produced by unbinding of half-quantum vortices.

  2. Kondo Screening and Fermi Surface in the Antiferromagnetic Metal Phase

    Science.gov (United States)

    Yamamoto, Seiji; Si, Qimiao

    2006-03-01

    We address the Kondo effect deep inside the antiferromagnetic metal phase of a Kondo lattice Hamiltonian with SU(2) invariance. The local- moment component is described in terms of a non-linear sigma model. The Fermi surface of the conduction electron component is taken to be sufficiently small, so that it is not spanned by the antiferromagnetic wavevector. The effective low energy form of the Kondo coupling simplifies drastically, corresponding to the uniform component of the magnetization that forward-scatters the conduction electrons on their own Fermi surface. We use a combined bosonic and fermionic (Shankar) renormalization group procedure to analyze this effective theory and study the Kondo screening and Fermi surface in the antiferromagnetic phase. The implications for the global magnetic phase diagram, as well as quantum critical points, of heavy fermion metals are discussed.

  3. Magnetic phase diagrams of classical triangular and kagome antiferromagnets.

    Science.gov (United States)

    Gvozdikova, M V; Melchy, P-E; Zhitomirsky, M E

    2011-04-27

    We investigate the effect of geometrical frustration on the H-T phase diagrams of the classical Heisenberg antiferromagnets on triangular and kagome lattices. The phase diagrams for the two models are obtained from large-scale Monte Carlo simulations. For the kagome antiferromagnet, thermal fluctuations are unable to lift degeneracy completely and stabilize translationally disordered multipolar phases. We find a substantial difference in the temperature scales of the order by disorder effect related to different degeneracy of the low- and the high-field classical ground states in the kagome antiferromagnet. In the low-field regime, the Kosterlitz-Thouless transition into a spin-nematic phase is produced by unbinding of half-quantum vortices.

  4. Role of the antiferromagnetic bulk spins in exchange bias

    Energy Technology Data Exchange (ETDEWEB)

    Schuller, Ivan K. [Center for Advanced Nanoscience and Physics Department, University of California San Diego, La Jolla, CA 92093 (United States); Morales, Rafael, E-mail: rafael.morales@ehu.es [Department of Chemical-Physics & BCMaterials, University of the Basque Country UPV/EHU (Spain); IKERBASQUE, Basque Foundation for Science, 48011 Bilbao (Spain); Batlle, Xavier [Departament Física Fonamental and Institut de Nanociència i Nanotecnologia, Universitat de Barcelona, c/ Martí i Franqués s/n, 08028 Barcelona, Catalonia (Spain); Nowak, Ulrich [Department of Physics, University of Konstanz, 78464 Konstanz (Germany); Güntherodt, Gernot [Physics Institute (IIA), RWTH Aachen University, Campus RWTH-Melaten, 52074 Aachen (Germany)

    2016-10-15

    This “Critical Focused Issue” presents a brief review of experiments and models which describe the origin of exchange bias in epitaxial or textured ferromagnetic/antiferromagnetic bilayers. Evidence is presented which clearly indicates that inner, uncompensated, pinned moments in the bulk of the antiferromagnet (AFM) play a very important role in setting the magnitude of the exchange bias. A critical evaluation of the extensive literature in the field indicates that it is useful to think of this bulk, pinned uncompensated moments as a new type of a ferromagnet which has a low total moment, an ordering temperature given by the AFM Néel temperature, with parallel aligned moments randomly distributed on the regular AFM lattice. - Highlights: • We address the role of bulk antiferromagnetic spins in the exchange bias phenomenon. • Significant experiments on how bulk AFM spins determine exchange bias are highlighted. • We explain the model that accounts for experimental results.

  5. Revealing the properties of Mn2Au for antiferromagnetic spintronics.

    Science.gov (United States)

    Barthem, V M T S; Colin, C V; Mayaffre, H; Julien, M-H; Givord, D

    2013-01-01

    The continuous reduction in size of spintronic devices requires the development of structures, which are insensitive to parasitic external magnetic fields, while preserving the magnetoresistive signals of existing systems based on giant or tunnel magnetoresistance. This could be obtained in tunnel anisotropic magnetoresistance structures incorporating an antiferromagnetic, instead of a ferromagnetic, material. To turn this promising concept into real devices, new magnetic materials with large spin-orbit effects must be identified. Here we demonstrate that Mn2Au is not a Pauli paramagnet as hitherto believed but an antiferromagnet with Mn moments of ~4 μB. The particularly large strength of the exchange interactions leads to an extrapolated Néel temperature well above 1,000 K, so that ground-state magnetic properties are essentially preserved up to room temperature and above. Combined with the existence of a significant in-plane anisotropy, this makes Mn2Au the most promising material for antiferromagnetic spintronics identified so far.

  6. Magnetization damping in noncollinear spin valves with antiferromagnetic interlayer couplings

    Science.gov (United States)

    Chiba, Takahiro; Bauer, Gerrit E. W.; Takahashi, Saburo

    2015-08-01

    We study the magnetic damping in the simplest of synthetic antiferromagnets, i.e., antiferromagnetically exchange-coupled spin valves, in the presence of applied magnetic fields that enforce noncolliear magnetic configurations. We formulate the dynamic exchange of spin currents in a noncollinear texture based on the spin-diffusion theory with quantum mechanical boundary conditions at the ferrromagnet/normal-metal interfaces and derive the Landau-Lifshitz-Gilbert equations coupled by the interlayer static and dynamic exchange interactions. We predict noncollinearity-induced additional damping that is modulated by an applied magnetic field. We compare theoretical results with published experiments.

  7. Multicritical point in a diluted bilayer Heisenberg quantum antiferromagnet.

    Science.gov (United States)

    Sandvik, Anders W

    2002-10-21

    The S=1/2 Heisenberg bilayer antiferromagnet with randomly removed interlayer dimers is studied using quantum Monte Carlo simulations. A zero-temperature multicritical point (p(*),g(*)) at the classical percolation density p=p(*) and interlayer coupling g(*) approximately equal 0.16 is demonstrated. The quantum critical exponents of the percolating cluster are determined using finite-size scaling. It is argued that the associated finite-temperature quantum critical regime extends to zero interlayer coupling and could be relevant for antiferromagnetic cuprates doped with nonmagnetic impurities.

  8. Magnetic relaxation in a suspension of antiferromagnetic nanoparticles

    Science.gov (United States)

    Raikher, Yu. L.; Stepanov, V. I.

    2008-09-01

    A kinetic model is proposed to describe the low-frequency magnetodynamics of antiferromagnetic nanoparticles suspended in a fluid. Because of their small size, apart from an anisotropic magnetic susceptibility typical of antiferromagnets, these particles also have a constant magnetic moment caused by sublattice decompensation. An orientational crossover takes place in such a nanosuspension (colloid) when magnetized by a constant field: the axes of easy particle magnetization that were initially aligned along the field become oriented perpendicularly. This effect changes significantly the characteristics of the system’s magnetic response: the dynamic susceptibility spectrum and the relaxation time in a pulsed field.

  9. Spin transport through the metallic antiferromagnet FeMn

    Science.gov (United States)

    Saglam, H.; Zhang, W.; Jungfleisch, M. B.; Sklenar, J.; Pearson, J. E.; Ketterson, J. B.; Hoffmann, A.

    2016-10-01

    We investigate spin transport through metallic antiferromagnets using measurements based on spin pumping combined with inverse spin Hall effects in N i80F e20/FeMn /W trilayers. The relatively large magnitude and opposite sign of spin Hall effects in W compared to FeMn enable an unambiguous detection of spin currents transmitted through the entire FeMn layer thickness. Using this approach we can detect two distinctively different spin transport regimes, which we associate with electronic and magnonic spin currents, respectively. The latter can extend to relatively large distances (≈9 nm) and is enhanced when the antiferromagnetic ordering temperature is close to the measurement temperature.

  10. Quantification of quantum discord in a antiferromagnetic Heisenberg compound

    Energy Technology Data Exchange (ETDEWEB)

    Singh, H., E-mail: chiranjib@iiserkol.ac.in; Chakraborty, T., E-mail: chiranjib@iiserkol.ac.in; Mitra, C., E-mail: chiranjib@iiserkol.ac.in [Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur Campus, Mohanpur -741252, Nadia, West Bengal (India)

    2014-04-24

    An experimental quantification of concurrence and quantum discord from heat capacity (C{sub p}) measurement performed over a solid state system has been reported. In this work, thermodynamic measurements were performed on copper nitrate (CN, Cu(NO{sub 3}){sub 2}⋅2.5H{sub 2}O) single crystals which is an alternating antiferromagnet Heisenberg spin 1/2 system. CN being a weak dimerized antiferromagnet is an ideal system to investigate correlations between spins. The theoretical expressions were used to obtain concurrence and quantum discord curves as a function of temperature from heat capacity data of a real macroscopic system, CN.

  11. On the interpretation of magnetization data for antiferromagnetic nanoparticles

    DEFF Research Database (Denmark)

    Madsen, Daniel Esmarch; Mørup, Steen; Hansen, Mikkel Fougt

    2006-01-01

    We have investigated the influence of anisotropy on the magnetization curves of antiferromagnetic nanoparticles. We show that if such curves are analyzed in a conventional way, i.e. using a Langevin function in combination with a linear term, this usually results in good quality fits......, but with an apparent temperature dependence of parameters such as the magnetic moment per particle and the antiferromagnetic susceptibility. In order to avoid the problems associated with anisotropy as well as volume/moment distributions we propose that the initial susceptibility is used when analyzing the temperature...... dependence of the magnetic moment....

  12. Uniaxial pressure dependence of the antiferromagnetic order in UPt3

    Science.gov (United States)

    van Dijk, N. H.; Rodière, P.; Fåk, B.; Huxley, A.; Flouquet, J.; Fernández-Díaz, M. T.; Yakhou, F.

    The weak antiferromagnetic order of the heavy-fermion superconductor UPt3 has been investigated by elastic neutron-scattering measurements under applied uniaxial pressure up to 6 kbar along the a and c axes of the hexagonal crystal structure. For p||c the small antiferromagnetically ordered moment of 0.02μB/U-atom shows a non-linear decrease for increasing pressures and is still not completely suppressed at the maximum applied pressure of 6 kbar. For p||a a significant increase in the magnetic Bragg peak intensity is observed, which suggests an incomplete domain repopulation and confirms the presence of a single-k structure.

  13. Antiferromagnetic Potts model on the Erdos-Renyi random graph

    CERN Document Server

    Contucci, Pierluig; Giardina', Cristian; Starr, Shannon

    2011-01-01

    We study the antiferromagnetic Potts model on the Erdos-Renyi random graph. By identifying a suitable interpolation structure and proving an extended variational principle we show that the replica symmetric solution is an upper bound for the limiting pressure which can be recovered in the framework of Derrida-Ruelle probability cascades. A comparison theorem with a mixed model made of a mean field Potts-antiferromagnet plus a Potts-Sherrington-Kirkpatrick model allows to show that the replica symmetric solution is exact at high temperatures.

  14. Spin waves in antiferromagnetic FeF2

    DEFF Research Database (Denmark)

    Hutchings, M T; Rainford, B.D.; Guggenheim, H J

    1970-01-01

    Spin-wave dispersion in antiferromagnetic FeF2 has been investigated by inelastic neutron scattering using a chopper time-of-flight spectrometer. The single mode observed has a relatively flat dispersion curve rising from 53 cm-1 at the zone centre to 79 cm-1 at the zone boundary. A spin Hamilton......Spin-wave dispersion in antiferromagnetic FeF2 has been investigated by inelastic neutron scattering using a chopper time-of-flight spectrometer. The single mode observed has a relatively flat dispersion curve rising from 53 cm-1 at the zone centre to 79 cm-1 at the zone boundary. A spin...

  15. Spin Hall magnetoresistance in antiferromagnet/normal metal bilayers

    KAUST Repository

    Manchon, Aurelien

    2017-01-01

    We investigate the emergence of spin Hall magnetoresistance in a magnetic bilayer composed of a normal metal adjacent to an antiferromagnet. Based on a recently derived drift diffusion equation, we show that the resistance of the bilayer depends on the relative angle between the direction transverse to the current flow and the Néel order parameter. While this effect presents striking similarities with the spin Hall magnetoresistance recently reported in ferromagnetic bilayers, its physical origin is attributed to the anisotropic spin relaxation of itinerant spins in the antiferromagnet.

  16. Internal energy and specific heat in a ferromagnetic-antiferromagnetic double layers

    Institute of Scientific and Technical Information of China (English)

    Jiang Wei; Guo An-Bang

    2007-01-01

    The internal energy and specific heat of a Heisenberg ferro- antiferromagnetic double-layer system are studied by using spin-wave theory and the retarded Green function method at low temperatures. Numerical results show that the antiferromagnetic intralayer coupling J2 has an important influence on internal energy and specific heat for a four-sublattice system with antiferromagnetic (or ferrimagnetic) interlayer couplings.

  17. Spin Transport and Dynamics in Antiferromagnetic Metals and Magnetic Insulators

    NARCIS (Netherlands)

    Swaving, A.C.|info:eu-repo/dai/nl/313938083

    2012-01-01

    It is demonstrated that in an antiferromagnetic metal a steady-state transport current generates a current-induced out-of-plane spin density, resulting in torques on the magnetization. This spin density is parameterized by a velocity that is proportional to the current. The generalization of the

  18. Competitive forms of symmetry breaking in linear antiferromagnetic systems

    NARCIS (Netherlands)

    Caspers, W.J.; Magnus, W.

    1985-01-01

    Two different forms of symmetry breaking are considered for linear antiferromagnetic systems (S = 1/2 ). Their relative stability is examined by considering small fluctuations in the harmonic oscillator approximation. Imaginary frequencies correspond with an unstable phase, and the ground state repr

  19. Excitations in a Two-Dimensional Random Antiferromagnet

    DEFF Research Database (Denmark)

    Birgeneau, R. J.; Walker, L. R.; Guggenheim, H. J.;

    1975-01-01

    Inelastic neutron scattering studies of the magnetic excitations in the planar Heisenberg random antiferromagnet Rb2Mn0.5Ni0.5F4 at 7K are reported. Two well-defined bands of excitations are observed. A simple mean crystal model is found to predict accurately the measured dispersion relations using...

  20. Thermoinduced magnetization and uncompensated spins in antiferromagnetic nanoparticles

    DEFF Research Database (Denmark)

    Madsen, Daniel Esmarch; Mørup, Steen

    2006-01-01

    We have investigated the combined effect of an uncompensated moment and the thermoinduced magnetization on the initial susceptibility of nanoparticles of antiferromagnetic materials. We find that for nanoparticles with small values of the anisotropy and exchange fields, the thermoinduced...... magnetization may be predominant at finite temperatures. In other cases the uncompensated moment may be predominant....

  1. Observation of Antiferromagnetic Resonance in an Organic Superconductor

    DEFF Research Database (Denmark)

    Torrance, J. B.; Pedersen, H. J.; Bechgaard, K.

    1982-01-01

    Anomalous microwave absorption has been observed in the organic superconductor TMTSF2AsF6 (TMTSF: tetramethyltetraselenafulvalene) below its metal-nonmetal transition near 12 K. This absorption is unambiguously identified as antiferromagnetic resonance by the excellent agreement between a spin...

  2. Onset of antiferromagnetism in heavy-fermion metals

    Science.gov (United States)

    Schroder; Aeppli; Coldea; Adams; Stockert; v. Lohneysen H; Bucher; Ramazashvili; Coleman

    2000-09-21

    There are two main theoretical descriptions of antiferromagnets. The first arises from atomic physics, which predicts that atoms with unpaired electrons develop magnetic moments. In a solid, the coupling between moments on nearby ions then yields antiferromagnetic order at low temperatures. The second description, based on the physics of electron fluids or 'Fermi liquids' states that Coulomb interactions can drive the fluid to adopt a more stable configuration by developing a spin density wave. It is at present unknown which view is appropriate at a 'quantum critical point' where the antiferromagnetic transition temperature vanishes. Here we report neutron scattering and bulk magnetometry measurements of the metal CeCu(6-x)Au(x), which allow us to discriminate between the two models. We find evidence for an atomically local contribution to the magnetic correlations which develops at the critical gold concentration (x(c) = 0.1), corresponding to a magnetic ordering temperature of zero. This contribution implies that a Fermi-liquid-destroying spin-localizing transition, unanticipated from the spin density wave description, coincides with the antiferromagnetic quantum critical point.

  3. Soliton dynamics in planar ferromagnets and anti-ferromagnets

    Institute of Scientific and Technical Information of China (English)

    LINFang-hua; SHATAHJalal

    2003-01-01

    The aim of this paper is to present a rigorous mathematical proof of the dynamical laws for the topological solitons( magnetic vortices) in ferromagnets and anti-ferromagnets. It is achieved through the conservation laws for the topological vorticity and the weak convergence methods.

  4. The three-state antiferromagnetic Potts model: scaling laws

    Energy Technology Data Exchange (ETDEWEB)

    Gottlob, A.P. [Kaiserslautern Univ. (Germany); Hasenbusch, M. [Cambridge Univ. (United Kingdom). Dept. of Applied Mathematics and Theoretical Physics (DAMTP)

    1995-04-01

    We present the results of a Monte Carlo study of the three-dimensional anti-ferromagnetic three-state Potts model. We computed the correlation length, the magnetic susceptibility and the specific heat for various coupling parameters in the high temperature phase of the model. From the scaling behaviour of these quantities we determine estimates for the critical temperature and critical exponents. ((orig.)).

  5. Ferromagnetic and antiferromagnetic order in bacterial vortex lattices

    Science.gov (United States)

    Wioland, Hugo; Woodhouse, Francis G.; Dunkel, Jörn; Goldstein, Raymond E.; Goldstein Lab Team

    2013-11-01

    In conventional electronic materials, spins can organize into ordered phases that give rise to ferromagnetic or antiferromagnetic behavior. Here, we report similar observations in a completely different system: a suspension of swimming bacteria. When a dense Bacillus subtilis suspension is confined to a small circular chamber, it can spontaneously form a stable vortex (``spin'') state that can persist for several minutes. By coupling up to 100 such chambers in microfluidic devices, we are able to realize bacterial spin lattices of different geometries. Depending on that geometry and the effective coupling strength between neighboring vortices, we observe the formation of stable ``antiferromagnetic'' and ``ferromagnetic'' bacterial vortex states, that appear to be controlled by the subtle competition between bacterial boundary layer flows and bulk dynamics.

  6. Quantum Nucleation of Antiferromagnetic Bubbles with Tetragonal and Hexagonal Symmetries

    Institute of Scientific and Technical Information of China (English)

    PAN Hui; ZHU Jia-Lin; L(U) Rong

    2004-01-01

    We study the quantum nucleation in a nanometer-scale antiferromagnet placed in a magnetic field at an arbitrary angle. We consider the magnetocrystalline anisotropy with tetragonal symmetry and that with hexagonal symmetry, respectively. Different structures of the tunneling barriers can be generated by the magnitude and the orientation of the magnetic field. We use the instanton method in the spin-coherent-state path-integral representation to calculate the dependence of the rate of quantum nucleation and the crossover temperature on the orientation and strength of the field for bulk solids and two-dimensional films of antiferromagnets, respectively. We find that the rate of quantum nucleation and the crossover temperature from thermal-to-quantum transitions depend on the orientation and strength of the external magnetic field distinctly, which can be tested by use of existing experimental techniques.

  7. Resonating Valence Bond states for low dimensional S=1 antiferromagnets

    Science.gov (United States)

    Liu, Zheng-Xin; Zhou, Yi; Ng, Tai-Kai

    2014-03-01

    We study S = 1 spin liquid states in low dimensions. We show that the resonating-valence-bond (RVB) picture of S = 1 / 2 spin liquid state can be generalized to S = 1 case. For S = 1 system, a many-body singlet (with even site number) can be decomposed into superposition of products of two-body singlets. In other words, the product states of two-body singlets, called the singlet pair states (SPSs), are over complete to span the Hilbert space of many-body singlets. Furthermore, we generalized fermionic representation and the corresponding mean field theory and Gutzwiller projected stats to S = 1 models. We applied our theory to study 1D anti-ferromagnetic bilinear-biquadratic model and show that both the ground states (including the phase transition point) and the excited states can be understood excellently well within the framework. Our method can be applied to 2D S = 1 antiferromagnets.

  8. Currentless reversal of Néel vector in antiferromagnets

    Science.gov (United States)

    Semenov, Yuriy G.; Li, Xi-Lai; Kim, Ki Wook

    2017-01-01

    The possibility of magnetization reversal via a bias-mediated perpendicular magnetic anisotropy is examined theoretically in an antiferromagnet. The numerical analyses based on a Néel vector formulation as well as the micromagnetic Landau-Lifshitz-Gilbert simulation reveal that the desired switching can be achieved through dynamical responses that are significantly different from their ferromagnetic counterparts. Instead of the usual precessional trajectories around the applied effective magnetic field, their motions are rather pendulum-like due to the layered magnetic sublattices with a strong antiparallel exchange interaction, where the inertial behavior plays a crucial role. The absence of spiral damping can also lead to faster relaxation by orders of magnitude. With no reliance on the current driven processes, the investigated mechanism is predicted with a low energy requirement of only a few aJ per switching operation in the antiferromagnets.

  9. Spin-transfer torque induced spin waves in antiferromagnetic insulators

    Science.gov (United States)

    Daniels, Matthew; Guo, Wei; Stocks, G. Malcolm; Xiao, Di; Xiao, Jiang

    2015-03-01

    We explore the possibility of exciting spin waves in insulating antiferromagnetic films by injecting spin current at the surface. We analyze both magnetically compensated and uncompensated interfaces. We find that the spin current induced spin-transfer torque can excite spin waves in insulating antiferromagnetic materials and that the chirality of the excited spin wave is determined by the polarization of the injected spin current. Furthermore, the presence of magnetic surface anisotropy can greatly increase the accessibility of these excitations. Supported by NSF EFRI-1433496 (M.W.D), U.S. DOE Office of Basic Energy Sciences, Materials Sciences and Engineering (D.X. & G.M.S.), Major State Basic Research Project of China and National Natural Science Foundation of China (W.G. and J.X.).

  10. Experimental and theoretical studies of nanoparticles of antiferromagnetic materials

    DEFF Research Database (Denmark)

    Mørup, Steen; Madsen, Daniel Esmarch; Frandsen, Cathrine

    2007-01-01

    The magnetic properties of nanoparticles of antiferromagnetic materials are reviewed. The magnetic structure is often similar to the bulk structure, but there are several examples of size-dependent magnetic structures. Owing to the small magnetic moments of antiferromagnetic nanoparticles......, the commonly used analysis of magnetization curves above the superparamagnetic blocking temperature may give erroneous results, because the distribution in magnetic moments and the magnetic anisotropy are not taken into account. We discuss how the magnetic dynamics can be studied by use of magnetization...... nanoparticles is usually negligible, and therefore such particles present a unique possibility to study exchange interactions between magnetic particles. The interactions can have a significant influence on both the magnetic dynamics and the magnetic structure. Nanoparticles can be attached with a common...

  11. Impurity-induced antiferromagnetic domains in the periodic Anderson model

    Science.gov (United States)

    Benali, A.; Bai, Z. J.; Curro, N. J.; Scalettar, R. T.

    2016-08-01

    A central feature of the periodic Anderson model is the competition between antiferromagnetism, mediated by the Ruderman-Kittel-Kasuya-Yosida interaction at small conduction electron-local electron hybridization V , and singlet formation at large V . At zero temperature, and in dimension d >1 , these two phases are separated by a quantum critical point Vc. We use quantum Monte Carlo (QMC) simulations to explore the effect of impurities which have a local hybridization V*Vc . We measure the suppression of singlet correlations and the antiferromagnetic correlations which form around the impurity, as well as the size of the resulting domain. Exact diagonalization calculations for linear chains allow us to verify that the qualitative features obtained at intermediate coupling and finite T persist to strong coupling and T =0 , regimes which are difficult to access with QMC. Our calculations agree qualitatively with NMR measurements in CeCoIn5 -xCdx .

  12. Gossamer superconductivity near antiferromagnetic Mott insulator in layered organic conductors.

    Science.gov (United States)

    Gan, J Y; Chen, Yan; Su, Z B; Zhang, F C

    2005-02-18

    Layered organic superconductors are on the verge of the Mott insulator. We use the Gutzwiller variational method to study a two-dimensional Hubbard model including a spin exchange coupling term as a minimal model for the compounds. The ground state is found to be a Gossamer superconductor at small on-site Coulomb repulsion U and an antiferromagnetic Mott insulator at large U, separated by a first order phase transition. Our theory is qualitatively consistent with major experiments reported in organic superconductors.

  13. Quantum Monte Carlo Study of Random Antiferromagnetic Heisenberg Chain

    OpenAIRE

    Todo, Synge; Kato, Kiyoshi; Takayama, Hajime

    1998-01-01

    Effects of randomness on the spin-1/2 and 1 antiferromagnetic Heisenberg chains are studied using the quantum Monte Carlo method with the continuous-time loop algorithm. We precisely calculated the uniform susceptibility, string order parameter, spatial and temporal correlation length, and the dynamical exponent, and obtained a phase diagram. The generalization of the continuous-time loop algorithm for the systems with higher-S spins is also presented.

  14. Spatially frustrated S = 1 Heisenberg antiferromagnet with single ion anisotropy

    Science.gov (United States)

    Pires, A. S. T.

    2016-10-01

    Using the SU(3) Schwinger boson formalism, I study the S = 1 square lattice Heisenberg antiferromagnet, at zero temperature, with spatially anisotropic nearest-neighbor couplings frustrated by a next-nearest neighbor interaction and single ion anisotropy. The phase diagram at zero temperature is presented. My calculations show two magnetically ordered phases separated by a quantum-disordered region for all values of the anisotropy.

  15. Polarized Neutron Reflectivity Simulation of Ferromagnet/ Antiferromagnet Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ki Yeon; Lee, Jeong Soo

    2008-02-15

    This report investigates the current simulating and fitting programs capable of calculating the polarized neutron reflectivity of the exchange-biased ferromagnet/antiferromagnet magnetic thin films. The adequate programs are selected depending on whether nonspin flip and spin flip reflectivities of magnetic thin films and good user interface are available or not. The exchange-biased systems such as Fe/Cr, Co/CoO, CoFe/IrMn/Py thin films have been simulated successfully with selected programs.

  16. Large-scale numerical investigations of the antiferromagnetic Heisenberg icosidodecahedron

    Energy Technology Data Exchange (ETDEWEB)

    Ummethum, Joerg [Department of Physics, Bielefeld University, P.O. Box 100131, D-33501 Bielefeld (Germany); Schnack, Juergen, E-mail: jschnack@uni-bielefeld.de [Department of Physics, Bielefeld University, P.O. Box 100131, D-33501 Bielefeld (Germany); Laeuchli, Andreas M. [Inst. f. Theoretische Physik, Innsbruck University, Technikerstr. 25, 6020 Innsbruck (Austria)

    2013-02-15

    We present up to date investigations of the antiferromagnetic Heisenberg icosidodecahedron by means of the density matrix renormalization group method. We compare our results with modern correlator product state as well as Lanczos calculations. - Highlights: Black-Right-Pointing-Pointer Results of unprecedented accuracy for energies and correlation functions of a frustrated spin system. Black-Right-Pointing-Pointer Relevance for a large set of magnetic molecules. Black-Right-Pointing-Pointer Demonstration of accuracy of DDMRG.

  17. Neutron Scattering Studies of Antiferromagnetic Correlations in Cuprates

    OpenAIRE

    Tranquada, John M.

    2005-01-01

    Neutron scattering studies have provided important information about the momentum and energy dependence of magnetic excitations in cuprate superconductors. Of particular interest are the recent indications of a universal magnetic excitation spectrum in hole-doped cuprates. That starting point provides motivation for reviewing the antiferromagnetic state of the parent insulators, and the destruction of the ordered state by hole doping. The nature of spin correlations in stripe-ordered phases i...

  18. Magnetization behavior of nanocrystalline systems combining ferromagnetic and antiferromagnetic phases

    Energy Technology Data Exchange (ETDEWEB)

    Loeffler, J.; Wagner, W.; Svygenhoven, H. van [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Meier, J.; Doudin, B.; Ansermet, J.P. [Ecole Polytechnique Federale, Lausanne (Switzerland)

    1997-09-01

    The magnetic properties of nanostructured materials on the basis of Fe and Ni have been investigated with a SQUID magnetometer, complementary to the small-angle neutron scattering study reported in the same volume. Measurements of the coercive field in a temperature range from 5 to 300 K confirm the validity of the random anisotropy model for our nanostructured systems. Furthermore, we obtain information about the presence and distribution of the antiferromagnetic oxides, joining the ferromagnetic grains. (author) 2 figs., 3 refs.

  19. Long range anti-ferromagnetic spin model for prebiotic evolution

    Energy Technology Data Exchange (ETDEWEB)

    Nokura, Kazuo [Shonan Institute of Technology, Fujisawa 251-8511 (Japan)

    2003-11-28

    I propose and discuss a fitness function for one-dimensional binary monomer sequences of macromolecules for prebiotic evolution. The fitness function is defined by the free energy of polymers in the high temperature random coil phase. With repulsive interactions among the same kind of monomers, the free energy in the high temperature limit becomes the energy function of the one-dimensional long range anti-ferromagnetic spin model, which is shown to have a dynamical phase transition and glassy states.

  20. Correlations between Kondo clouds in nearly antiferromagnetic Kondo lattices

    Energy Technology Data Exchange (ETDEWEB)

    Kiselev, M.N. E-mail: kiselev@physik.uni-wuerzburg.de; Kikoin, K.A

    2004-05-01

    We discuss a novel fluctuational mechanism explaining the physics of nearly antiferromagnetic Kondo lattices (KL). The effective action for KL model is expressed in terms of Bose operators responsible for paramagnetic excitations and semi-bosonic fields describing the dynamic Kondo clouds created by conduction electrons around local spin. The gauge invariant resonance valence bond theory of interacting Kondo clouds describes the spin liquid with strong critical fluctuations imitating itinerant fluctuation magnetism of Moriya type.

  1. Fermion Bound States Around Skyrmions in Doped Antiferromagnets

    Institute of Scientific and Technical Information of China (English)

    寇谡鹏

    2003-01-01

    We show the skyrmion effects in doped antiferromagnets for the uniform flux phase. The low-energy effective theory of the t′-J model can be mapped onto the massive quantum electrodynamics. There exist Fermion bound states around skyrmions. For each sublattice, there exist induced fractional fermion numbers around the skyrmions. The total induced fermion number is zero due to the "cancelling effect" between two sublattices with opposite charges.

  2. Two-step flux penetration in classic antiferromagnetic superconductor

    OpenAIRE

    Krzyszton, T.; Rogacki, K.

    2001-01-01

    The influence of antiferromagnetic order on the mixed state of a superconductor may result in creation of spin-flop domains along vortices. This may happen when an external magnetic field is strong enough to flip over magnetic moments in the vortex core from their ground state configuration. The formation of domain structure causes modification of the surface energy barrier, and creation of the new state in which magnetic flux density is independent of the applied field. The modified surface ...

  3. Academic Meeting Scheduling Using an Antiferromagnetic Potts Model

    Science.gov (United States)

    Kudo, Kazue

    2017-07-01

    Scheduling parallel sessions of an academic meeting is a complicated task. If each presentation is assigned to an appropriate session, an antiferromagnetic Potts model can be used for semi-automatic timetabling. The timetabling method proposed here is based on graph coloring and includes additional constraints to be considered in a practical situation. We examine the feasibility of semi-automatic timetabling in some practical examples.

  4. Electrical manipulation of a ferromagnet by an antiferromagnet

    Science.gov (United States)

    Tshitoyan, V.; Ciccarelli, C.; Mihai, A. P.; Ali, M.; Irvine, A. C.; Moore, T. A.; Jungwirth, T.; Ferguson, A. J.

    Several recent studies of antiferromagnetic (AFM) spintronics have focused on transmission and detection of spin-currents in AFMs. Efficient spin transmission through AFMs was inferred from experiments in FM/AFM/NM (normal metal) structures. Measurements in FM/AFM bilayers have demonstrated that a metallic AFM can also act as an efficient ISHE detector of the spin-current, with spin-Hall angles comparable to heavy NMs. Here we demonstrate that an antiferromagnet can be employed for a highly efficient electrical manipulation of a ferromagnet. We use an all-electrical excitation and detection technique of ferromagnetic resonance in a NiFe/IrMn bilayer. We observe antidamping-like spin torque acting on the NiFe generated by the in-plane current driven through the IrMn antiferromagnet. A large enhancement of the torque, characterized by an effective spin-Hall angle exceeding most heavy transition metals, correlates with the presence of the exchange-bias field at the NiFe/IrMn interface. It highlights that, in addition to strong spin-orbit coupling, the AFM order in IrMn governs the observed phenomenon.

  5. Large anomalous Hall effect in a half-Heusler antiferromagnet

    Science.gov (United States)

    Suzuki, T.; Chisnell, R.; Devarakonda, A.; Liu, Y.-T.; Feng, W.; Xiao, D.; Lynn, J. W.; Checkelsky, J. G.

    2016-12-01

    The quantum mechanical (Berry) phase of the electronic wavefunction plays a critical role in the anomalous and spin Hall effects, including their quantized limits. While progress has been made in understanding these effects in ferromagnets, less is known in antiferromagnetic systems. Here we present a study of antiferromagnet GdPtBi, whose electronic structure is similar to that of the topologically non-trivial HgTe (refs ,,), and where the Gd ions offer the possibility to tune the Berry phase via control of the spin texture. We show that this system supports an anomalous Hall angle ΘAH > 0.1, comparable to the largest observed in bulk ferromagnets and significantly larger than in other antiferromagnets. Neutron scattering measurements and electronic structure calculations suggest that this effect originates from avoided crossing or Weyl points that develop near the Fermi level due to a breaking of combined time-reversal and lattice symmetries. Berry phase effects associated with such symmetry breaking have recently been explored in kagome networks; our results extend this to half-Heusler systems with non-trivial band topology. The magnetic textures indicated here may also provide pathways towards realizing the topological insulating and semimetallic states predicted in this material class.

  6. Neutron scattering studies of three one-dimensional antiferromagnets

    CERN Document Server

    Kenzelmann, M

    2001-01-01

    observed in the disordered phase of spin-1/2 chains. The magnetic order of the one-dimensional spin-1/2 XY antiferromagnet Cs sub 2 CoCl sub 4 was investigated using neutron diffraction. The magnetic structure has an ordering wave-vector (0, 0.5, 0.5) for T < 217 mK and the magnetic structure is a non-linear structure with the magnetic moments at a small angle to the b axis. Above a field of H = 2.1 T the magnetic order collapses in an apparent first order phase transition, suggesting a transition to a spin-liquid phase. Low-dimensional magnets with low-spin quantum numbers are ideal model systems for investigating strongly interacting macroscopic quantum ground states and their non-linear spin excitations. This thesis describes neutron scattering experiments of three one-dimensional low-spin antiferromagnets where strong quantum fluctuations lead to highly-correlated ground states and unconventional cooperative spin excitations. The excitation spectrum of the antiferromagnetic spin-1 Heisenberg chain CsNi...

  7. Partial Ferrimagnetism in S = 1/2 Heisenberg Ladders with a Ferromagnetic Leg, an Antiferromagnetic Leg, and Antiferromagnetic Rungs

    Science.gov (United States)

    Sekiguchi, Kazutaka; Hida, Kazuo

    2017-08-01

    Ground-state and finite-temperature properties of S = 1/2 Heisenberg ladders with a ferromagnetic leg, an antiferromagnetic leg, and antiferromagnetic rungs are studied. It is shown that a partial ferrimagnetic phase extends over a wide parameter range in the ground state. The numerical results are supported by an analytical calculation based on a mapping onto the nonlinear σ model and a perturbation calculation from the strong-rung limit. It is shown that the partial ferrimagnetic state is a spontaneously magnetized Tomonaga-Luttinger liquid with incommensurate magnetic correlation, which is confirmed by a DMRG calculation. The finite-temperature magnetic susceptibility is calculated using the thermal pure quantum state method. It is suggested that the susceptibility diverges as T-2 in the ferrimagnetic phases as in the case of ferromagnetic Heisenberg chains.

  8. Metallic magnets without inversion symmetry and antiferromagnetic quantum critical points

    Energy Technology Data Exchange (ETDEWEB)

    Fischer, I.A.

    2006-07-01

    This thesis focusses on two classes of systems that exhibit non-Fermi liquid behaviour in experiments: we investigated aspects of chiral ferromagnets and of antiferromagnetic metals close to a quantum critical point. In chiral ferromagnets, the absence of inversion symmetry makes spin-orbit coupling possible, which leads to a helical modulation of the ferromagnetically ordered state. We studied the motion of electrons in the magnetically ordered state of a metal without inversion symmetry by calculating their generic band-structure. We found that spin-orbit coupling, although weak, has a profound effect on the shape of the Fermi surface: On a large portion of the Fermi surface the electron motion parallel to the helix practically stops. Signatures of this effect can be expected to show up in measurements of the anomalous Hall effect. Recent neutron scattering experiments uncovered the existence of a peculiar kind of partial order in a region of the phase diagram adjacent to the ordered state of the chiral ferromagnet MnSi. Starting from the premise that this partially ordered state is a thermodynamically distinct phase, we investigated an extended Ginzburg-Landau theory for chiral ferromagnets. In a certain parameter regime of the Ginzburg-Landau theory we identified crystalline phases that are reminiscent of the so-called blue phases in liquid crystals. Many antiferromagnetic heavy-fermion systems can be tuned into a regime where they exhibit non-Fermi liquid exponents in the temperature dependence of thermodynamic quantities such as the specific heat capacity; this behaviour could be due to a quantum critical point. If the quantum critical behaviour is field-induced, the external field does not only suppress antiferromagnetism but also induces spin precession and thereby influences the dynamics of the order parameter. We investigated the quantum critical behavior of clean antiferromagnetic metals subject to a static, spatially uniform external magnetic field. We

  9. Magnetic field induced switching of the antiferromagnetic order parameter in thin films of magnetoelectric chromia

    Science.gov (United States)

    Fallarino, Lorenzo; Berger, Andreas; Binek, Christian

    2015-02-01

    A Landau-theoretical approach is utilized to model the magnetic field induced reversal of the antiferromagnetic order parameter in thin films of magnetoelectric antiferromagnets. A key ingredient of this peculiar switching phenomenon is the presence of a robust spin polarized state at the surface of the antiferromagnetic films. Surface or boundary magnetization is symmetry allowed in magnetoelectric antiferromagnets and experimentally established for chromia thin films. It couples rigidly to the antiferromagnetic order parameter and its Zeeman energy creates a pathway to switch the antiferromagnet via magnetic field application. In the framework of a minimalist Landau free energy expansion, the temperature dependence of the switching field and the field dependence of the transition width are derived. Least-squares fits to magnetometry data of (0001 ) textured chromia thin films strongly support this model of the magnetic reversal mechanism.

  10. Mn2Au: body-centered-tetragonal bimetallic antiferromagnets grown by molecular beam epitaxy.

    Science.gov (United States)

    Wu, Han-Chun; Liao, Zhi-Min; Sofin, R G Sumesh; Feng, Gen; Ma, Xiu-Mei; Shick, Alexander B; Mryasov, Oleg N; Shvets, Igor V

    2012-12-11

    Mn(2)Au, a layered bimetal, is successfully grown using molecular beam epitaxy (MBE). The experiments and theoretical calculations presented suggest that Mn(2)Au film is antiferromagnetic with a very low critical temperature. The antiferromagnetic nature is demonstrated by measuring the exchange-bias effect of Mn(2)Au/Fe bilayers. This study establishes a primary basis for further research of this new antiferromagnet in spin-electronic device applications.

  11. Undulatory Variation of Antiferromagnetic Strength with Magnetic Field Based on Hubbard Model Hamiltonian

    OpenAIRE

    Doh, Hyeonjin; Salk, Sung-Ho Suck

    1996-01-01

    Using the Hubbard model Hamiltonian in a mean field level, we examine the variation of antiferromagnetic strength with applied magnetic field. It is demonstrated that minima in the antiferromagnetic strength exist at the the even integer denominator values of rational number for magnetic flux per plaquette. The undulatory behavior of antiferromagnetic strength with the external magnetic field is found. It is seen to be related to the undulatory net statistical phase owing to the influence of ...

  12. Reversible optical switching of antiferromagnetism in TbMnO3

    Science.gov (United States)

    Manz, Sebastian; Matsubara, Masakazu; Lottermoser, Thomas; Büchi, Jonathan; Iyama, Ayato; Kimura, Tsuyoshi; Meier, Dennis; Fiebig, Manfred

    2016-10-01

    Lasers can be used to control the magnetization of a ferromagnet via optically driven thermal and electronic excitation. Transfer of this concept to antiferromagnets is appealing because of the increasing technological interest in antiferromagnetism. Controlling spin structures in antiferromagnets is challenging, however, because of their zero magnetization. In a proof-of-principle experiment we demonstrate that optical control of antiferromagnetic domains is nevertheless possible. We reverse the antiferromagnetic order parameter in multiferroic TbMnO3 repeatedly, using light pulses of two different colours. Switching depends on a unique relation between the wavelength of the light, its optical absorption and the electric polarization field induced by the antiferromagnetic order of TbMnO3. We then demonstrate sequential laser-controlled writing and erasure of antiferromagnetic domains. The universality of reversible optical antiferromagnetic switching is derived by Monte Carlo simulations. Opto-magnetism is thus complemented by an important degree of freedom, namely local control of antiferromagnetism by means of light.

  13. Spin injection and absorption in antiferromagnets (Conference Presentation)

    Science.gov (United States)

    Frangou, Lamprini; Merodio, Pablo; Ghosh, Abhijit; Oyarzun, Simon; Auffret, Stephane; Ebels, Ursula; Chshiev, Mair; Bea, Helene; Vila, Laurent; Bailey, William E.; Gambarelli, Serge; Baltz, Vincent

    2016-10-01

    The antiferromagnetic order is expected to have a high potential in next-generation spintronic applications. It is resistant to perturbation by magnetic fields, produces no stray fields, displays ultrafast dynamics and may generate large magneto-transport effects. In spintronic materials, spin currents are key to unravelling spin dependent transport phenomena. Here, spin pumping results from the non-equilibrium magnetization dynamics of a ferromagnetic spin injector, which pumps a spin current into an adjacent spin sink. This spin sink absorbs the current to an extent which depends on its spin-dependent properties. The properties of the spin sink can be recorded either through the changes induced in ferromagnetic damping or through direct electrical means, such as by measuring the inverse spin Hall voltage. In this talk, we will deal with the injection of a spin current in thin antiferromagnetic sinks. Measurements of the spin penetration depths and absorption mechanisms were obtained for polycrystalline Ir20Mn80 and Fe50Mn50 films (Appl. Phys. Lett. 104, 032406 (2014)). More interestingly, spins propagate more efficiently in layers where the magnetic order is fluctuating rather than static. The experimental data were compared to some of the recently developed theories and converted into interfacial spin mixing conductance enhancements. These findings help us progress towards the development of more efficient spin sources, while also providing an alternative method to probe magnetic phase transitions (Phys. Rev. Lett. in press (2016)). This type of alternative method is particularly needed to deal with the case of thin materials with no net magnetic moments, such as thin antiferromagnets.

  14. Spin-Transfer-Torques at a Ferromagnet/Antiferromagnet Interface

    Science.gov (United States)

    Tsoi, Maxim

    2009-03-01

    Spintronics in ferromagnetic systems is built on a complementary set of phenomena in which the magnetic configuration of the system influences its transport properties and vice versa. Giant magnetoresistance (GMR) [1] and spin- transfer-torque (STT) [2] phenomena are typical examples of such interconnections. Recently, MacDonald and co-workers [3] predicted that corresponding effects ought to occur in systems where ferromagnetic (F) components are replaced by antiferromagnets (AFM). I will present our experimental search for these new AFM effects which may potentially lead to a new all-antiferromagnetic spintronics where antiferromagnets are used in place of ferromagnets. In particular I will focus on our experiments with exchange-biased spin valves [4] where extreme current densities were found to affect the exchange bias at F/AFM interface [5-7]. As exchange bias is known to be associated with interfacial AFM magnetic moments, our observation can be taken as the first evidence of STT effect in AFM materials. [4pt] [1] M. N. Baibich et al., Phys. Rev. Lett. 61, 2472 (1988); G. Binasch et al., Phys. Rev. B 39, 4828 (1989). [0pt] [2] J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996); L. Berger, J. Appl. Phys. 81, 4880 (1997); M. Tsoi et al., Phys. Rev. Lett. 80, 4281 (1998). [0pt] [3] A. S. N'uñez et al., Phys. Rev. B 73, 214426 (2006); [0pt] [4] Z. Wei et al., Phys. Rev. Lett. 98, 116603 (2007). [0pt] [5] S. Urazhdin and N. Anthony, Phys. Rev. Lett. 99, 046602 (2007). [0pt] [6] X-L.Tang et al., Appl. Phys. Lett. 91, 122504 (2007). [0pt] [7] N. V. Dai et al., Phys. Rev. B77, 132406 (2008).

  15. Antiferromagnetic phase transition and spin correlations in NiO

    DEFF Research Database (Denmark)

    Chatterji, Tapan; McIntyre, G.J.; Lindgård, Per-Anker

    2009-01-01

    We have investigated the antiferromagnetic (AF) phase transition and spin correlations in NiO by high-temperature neutron diffraction below and above TN. We show that AF phase transition is a continuous second-order transition within our experimental resolution. The spin correlations manifested...... by this process. We determined the critical exponents =0.328±0.002 and =0.64±0.03 and the Néel temperature TN=530±1 K. These critical exponents suggest that NiO should be regarded as a 3dXY system...

  16. Critical Behaviour of a Two-Dimensional Random Antiferromagnet

    DEFF Research Database (Denmark)

    Als-Nielsen, Jens Aage; Birgeneau, R. J.; Guggenheim, H. J.

    1976-01-01

    A neutron scattering study of the order parameter, correlation length and staggered susceptibility of the two-dimensional random antiferromagnet Rb2Mn0.5Ni0.5F4 is reported. The system is found to exhibit a well-defined phase transition with critical exponents identical to those of the isomorphou...... pure materials K2NiF4 and K2MnF4. Thus, in these systems, which have the asymptotic critical behaviour of the two-dimensional Ising model, randomness has no measurable effect on the phase-transition behaviour....

  17. Phase Diagram of Antiferromagnetically Exchange-Coupled Bilayer

    Institute of Scientific and Technical Information of China (English)

    GUO Guang-Hua; ZHANG Guang-Fu; SUN Li-Yuan; Peter A. J. de Groot

    2008-01-01

    Magnetic hysteresis properties of antiferromagnetically exchange-coupled bilayer structures, in which the two magnetic layers have different magnetic parameters and thicknesses, are studied within the framework of the Stoner-Wohifarth model. Analytical expressions for the switching fields corresponding to the linear magnetic states are obtained. By adjusting the magnetic parameters or thicknesses of layers, nine different types of easyaxis hysteresis loops may exist. The phase diagram of easy-axis hysteresis loops is mapped in the k,1 and k,2 plane, where k,1 and k,2 are the ratios of magnetic anisotropy to the interlayer exchange coupling of the two magnetic layers, respectively.

  18. Symmetry Reduction in the Quantum Kagome Antiferromagnet Herbertsmithite

    Science.gov (United States)

    Zorko, A.; Herak, M.; Gomilšek, M.; van Tol, J.; Velázquez, M.; Khuntia, P.; Bert, F.; Mendels, P.

    2017-01-01

    Employing complementary torque magnetometry and electron spin resonance on single crystals of herbertsmithite, the closest realization to date of a quantum kagome antiferromagnet featuring a spin-liquid ground state, we provide novel insight into different contributions to its magnetism. At low temperatures, two distinct types of defects with different magnetic couplings to the kagome spins are found. Surprisingly, their magnetic response contradicts the threefold symmetry of the ideal kagome lattice, suggesting the presence of a global structural distortion that may be related to the establishment of the spin-liquid ground state.

  19. Quenching the haldane gap in spin-1 Heisenberg antiferromagnets.

    Science.gov (United States)

    Wierschem, Keola; Sengupta, Pinaki

    2014-06-20

    We consider a quasi-one-dimensional system of spin-1 Heisenberg antiferromagnetic chains in two-dimensional and three-dimensional hypercubic lattices with interchain coupling J and uniaxial single-ion anisotropy D. Using large-scale numerical simulations, we map out the J-D phase diagram and investigate the low-lying excitations of the Haldane phase in the J≪1 limit. We also provide direct evidence that the Haldane phase remains a nontrivial symmetry-protected topological state for small but finite J.

  20. Yang-Lee Circle Theorem for an Antiferromagnetic Heisenberg Ladder

    Institute of Scientific and Technical Information of China (English)

    王先智

    2001-01-01

    The Yang-Lee zeros of an antiferromagnetic Heisenberg ladder model are determined. It is found that if J4≤0 Yang-Lee zeros are located on the unit circle and on the negative real axis in the complex activity plane. In particular, if J4≤0 and 2J2≥J4, Yang-Lee zeros are located on the unit circle and the Yang-Lee circle theorem is valid. If J4 > 0, Yang-Lee zeros are located on some complicated curves.

  1. Antiferromagnetic exchange and spin-fluctuation pairing in cuprate superconductors

    Science.gov (United States)

    Plakida, Nikolay M.

    2006-01-01

    A microscopic theory of superconductivity is formulated within an effective p-d Hubbard model for a CuO2 plane. By applying the Mori-type projection technique, the Dyson equation is derived for the Green functions in terms of Hubbard operators. The antiferromagnetic exchange caused by interband hopping results in pairing of all carries in the conduction subband and high Tc proportional to the Fermi energy. Kinematic interaction in intraband hopping is responsible for the conventional spin-fluctuation pairing. Numerical solution of the gap equation proves the d-wave gap symmetry and defines Tc doping dependence. Oxygen isotope shift and pressure dependence of Tc are also discussed.

  2. Dynamical Structure Factors of quasi-one-dimensional antiferromagnets

    Science.gov (United States)

    Hagemans, Rob; Caux, Jean-Sébastien; Maillet, Jean Michel

    2007-03-01

    For a long time it has been impossible to accurately calculate the dynamical structure factors (spin-spin correlators as a function of momentum and energy) of quasi-one-dimensional antiferromagnets. For integrable Heisenberg chains, the recently developed ABACUS method (a first-principles computational approach based on the Bethe Ansatz) now yields highly accurate (over 99% of the sum rule) results for the DSF for finite chains, allowing for a very precise description of neutron-scattering data over the full momentum and energy range. We show remarkable agreement between results obtained with ABACUS and experiment.

  3. Domain-wall spin dynamics in kagome antiferromagnets.

    Science.gov (United States)

    Lhotel, E; Simonet, V; Ortloff, J; Canals, B; Paulsen, C; Suard, E; Hansen, T; Price, D J; Wood, P T; Powell, A K; Ballou, R

    2011-12-16

    We report magnetization and neutron scattering measurements down to 60 mK on a new family of Fe based kagome antiferromagnets, in which a strong local spin anisotropy combined with a low exchange path network connectivity lead to domain walls intersecting the kagome planes through strings of free spins. These produce unfamiliar slow spin dynamics in the ordered phase, evolving from exchange-released spin flips towards a cooperative behavior on decreasing the temperature, probably due to the onset of long-range dipolar interaction. A domain structure of independent magnetic grains is obtained that could be generic to other frustrated magnets.

  4. Propagation and ghosts in the classical kagome antiferromagnet.

    Science.gov (United States)

    Robert, J; Canals, B; Simonet, V; Ballou, R

    2008-09-12

    We investigate the classical spin dynamics of the kagome antiferromagnet by combining Monte Carlo and spin dynamics simulations. We show that this model has two distinct low temperature dynamical regimes, both sustaining propagative modes. The expected gauge invariance type of the low energy, low temperature, out-of-plane excitations is also evidenced in the nonlinear regime. A detailed analysis of the excitations allows us to identify ghosts in the dynamical structure factor, i.e., propagating excitations with a strongly reduced spectral weight. We argue that these dynamical extinction rules are of geometrical origin.

  5. Density matrix renormalization group numerical study of the kagome antiferromagnet.

    Science.gov (United States)

    Jiang, H C; Weng, Z Y; Sheng, D N

    2008-09-12

    We numerically study the spin-1/2 antiferromagnetic Heisenberg model on the kagome lattice using the density-matrix renormalization group method. We find that the ground state is a magnetically disordered spin liquid, characterized by an exponential decay of spin-spin correlation function in real space and a magnetic structure factor showing system-size independent peaks at commensurate magnetic wave vectors. We obtain a spin triplet excitation gap DeltaE(S=1)=0.055+/-0.005 by extrapolation based on the large size results, and confirm the presence of gapless singlet excitations. The physical nature of such an exotic spin liquid is also discussed.

  6. Antiferromagnetic Mn 50Fe 50 wire with large magnetostriction

    Science.gov (United States)

    He, Aina; Ma, Tianyu; Zhang, Jingjing; Luo, Wei; Yan, Mi

    2009-11-01

    This work presents a study on the relation between the fiber texture and the magnetostrictive performance in an antiferromagnetic Mn 50Fe 50 alloy wire, which was prepared through the combining process of hot rolling and cold drawing. The face-centered cubic (fcc) crystal structure can be retained during the plastic deformation process. Mixed fiber textures consisting of both and components were formed along the drawing direction (DD) in the wire. A large magnetostriction of 750 ppm was obtained along DD under 1.2 T, which can be ascribed to the single γ phase and the formation of preferred crystal orientation.

  7. High-field spin dynamics of antiferromagnetic quantum spin chains

    DEFF Research Database (Denmark)

    Enderle, M.; Regnault, L.P.; Broholm, C.;

    2000-01-01

    The characteristic internal order of macroscopic quantum ground states in one-dimensional spin systems is usually not directly accessible, but reflected in the spin dynamics and the field dependence of the magnetic excitations. In high magnetic fields quantum phase transitions are expected. We...... present recent work on the high-field spin dynamics of the S = I antiferromagnetic Heisenberg chains NENP (Haldane ground state) and CsNiCl3 (quasi-1D HAF close to the quantum critical point), the uniform S = 1/2 chain CTS, and the spin-Peierls system CuGeO3. (C) 2000 Elsevier Science B,V. All rights...

  8. Superparamagnetic behavior of antiferromagnetic six lines ferrihydrite nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Rani, Chandni, E-mail: chandni@thapar.edu; Tiwari, S.D.

    2017-05-15

    Magnetic behavior of 5 nm antiferromagnetic six lines ferrihydrite particles is reported. The magnetization as a function of applied magnetic field data at 100 K are fitted to the modified Langevin function without and with considering a distribution in particle magnetic moment covering different ranges of applied magnetic field strength. The resulting fit parameters are analyzed and compared. In the first case fit parameters are found to be strongly dependent on the strength of applied magnetic field. But the fit parameters are found to be independent of applied magnetic field strength in the later case.

  9. Quantum phase transition between cluster and antiferromagnetic states

    CERN Document Server

    Son, Wonmin; Fazio, Rosario; Hamma, Alioscia; Pascazio, Saverio; Vedral, Vlatko

    2011-01-01

    We study a Hamiltonian system describing a three spin-1/2 cluster-like interaction competing with an Ising-like exchange. We show that the ground state in the cluster phase possesses symmetry protected topological order. A continuous quantum phase transition occurs as result of the competition between the cluster and Ising terms. At the critical point the Hamiltonian is self-dual. The geometric entanglement is also studied. Our findings in one dimension corroborate the analysis of the two dimensional generalization of the system, indicating, at a mean field level, the presence of a direct transition between an antiferromagnetic and a valence bond solid ground state.

  10. Phase transitions in antiferromagnets with a NaCl structure

    Energy Technology Data Exchange (ETDEWEB)

    Kassan-Ogly, F.A. [Institute of Metal Physics, Ural Division, Russian Academy of Sciences, ul. S.Kovalevskoi 18, Ekaterinburg 620219 (Russian Federation)]. E-mail: felix.kassan-ogly@imp.uran.ru; Filippov, B.N. [Institute of Metal Physics, Ural Division, Russian Academy of Sciences, ul. S.Kovalevskoi 18, Ekaterinburg 620219 (Russian Federation)

    2006-05-15

    A revised derivation scheme of possible magnetic structures in an FCC lattice with the nearest- and next-nearest-neighbor interactions taken into account is proposed. A model of simultaneous magnetic and structural phase transitions of the first order is developed for antiferromagnets with a NaCl structure and with a strong cubic magnetic anisotropy on the base of synthesis of magnetic modified 6-state Potts model and theoretical models of structural phase transitions in cubic crystals. It is shown that the high-temperature diffuse magnetic scattering of neutrons transforms into magnetic Bragg reflections below Neel point.

  11. Phase transitions in antiferromagnets with a NaCl structure

    Science.gov (United States)

    Kassan-Ogly, F. A.; Filippov, B. N.

    2006-05-01

    A revised derivation scheme of possible magnetic structures in an FCC lattice with the nearest- and next-nearest-neighbor interactions taken into account is proposed. A model of simultaneous magnetic and structural phase transitions of the first order is developed for antiferromagnets with a NaCl structure and with a strong cubic magnetic anisotropy on the base of synthesis of magnetic modified 6-state Potts model and theoretical models of structural phase transitions in cubic crystals. It is shown that the high-temperature diffuse magnetic scattering of neutrons transforms into magnetic Bragg reflections below Néel point.

  12. Z2 antiferromagnetic topological insulators with broken C4 symmetry

    Science.gov (United States)

    Bègue, Frédéric; Pujol, Pierre; Ramazashvili, Revaz

    2017-04-01

    A two-dimensional topological insulator may arise in a centrosymmetric commensurate Néel antiferromagnet (AF), where staggered magnetization breaks both the elementary translation and time reversal, but retains their product as a symmetry. Fang et al. [6] proposed an expression for a Z2 topological invariant to characterize such systems. Here, we show that this expression does not allow to detect all the existing phases if a certain lattice symmetry is lacking. We implement numerical techniques to diagnose topological phases of a toy Hamiltonian, and verify our results by computing the Chern numbers of degenerate bands, and also by explicitly constructing the edge states, thus illustrating the efficiency of the method.

  13. Antiferromagnetism and d-wave superconductivity in the Hubbard model

    Energy Technology Data Exchange (ETDEWEB)

    Krahl, H.C.

    2007-07-25

    The two-dimensional Hubbard model is a promising effective model for the electronic degrees of freedom in the copper-oxide planes of high temperature superconductors. We present a functional renormalization group approach to this model with focus on antiferromagnetism and d-wave superconductivity. In order to make the relevant degrees of freedom more explicitly accessible on all length scales, we introduce composite bosonic fields mediating the interaction between the fermions. Spontaneous symmetry breaking is reflected in a non-vanishing expectation value of a bosonic field. The emergence of a coupling in the d-wave pairing channel triggered by spin wave fluctuations is demonstrated. Furthermore, the highest temperature at which the interaction strength for the electrons diverges in the renormalization flow is calculated for both antiferromagnetism and d-wave superconductivity over a wide range of doping. This ''pseudo-critical'' temperature signals the onset of local ordering. Moreover, the temperature dependence of d-wave superconducting order is studied within a simplified model characterized by a single coupling in the d-wave pairing channel. The phase transition within this model is found to be of the Kosterlitz-Thouless type. (orig.)

  14. Theory of the spin Seebeck effect in antiferromagnets

    Science.gov (United States)

    Rezende, S. M.; Rodríguez-Suárez, R. L.; Azevedo, A.

    2016-01-01

    The spin Seebeck effect (SSE) consists in the generation of a spin current by a temperature gradient applied in a magnetic film. The SSE is usually detected by an electric voltage generated in a metallic layer in contact with the magnetic film resulting from the conversion of the spin current into charge current by means of the inverse spin Hall effect. The SSE has been widely studied in bilayers made of the insulating ferrimagnet yttrium iron garnet (YIG) and metals with large spin-orbit coupling such as platinum. Recently the SSE has been observed in bilayers made of the antiferromagnet Mn F2 and Pt, revealing dependences of the SSE voltage on temperature and field very different from the ones observed in YIG/Pt. Here we present a theory for the SSE in structures with an antiferromagnetic insulator (AFI) in contact with a normal metal (NM) that relies on the bulk magnon spin current created by the temperature gradient across the thickness of the AFI/NM bilayer. The theory explains quite well the measured dependences of the SSE voltage on the sample temperature and on the applied magnetic field in Mn F2/Pt .

  15. Spin Seebeck effect through antiferromagnetic NiO

    Science.gov (United States)

    Prakash, Arati; Brangham, Jack; Yang, Fengyuan; Heremans, Joseph P.

    2016-07-01

    We report temperature-dependent spin Seebeck measurements on Pt/YIG bilayers and Pt/NiO/YIG trilayers, where YIG (yttrium iron garnet, Y3F e5O12 ) is an insulating ferrimagnet and NiO is an antiferromagnet at low temperatures. The thickness of the NiO layer is varied from 0 to 10 nm. In the Pt/YIG bilayers, the temperature gradient applied to the YIG stimulates dynamic spin injection into the Pt, which generates an inverse spin Hall voltage in the Pt. The presence of a NiO layer dampens the spin injection exponentially with a decay length of 2 ± 0.6 nm at 180 K. The decay length increases with temperature and shows a maximum of 5.5 ± 0.8 nm at 360 K. The temperature dependence of the amplitude of the spin Seebeck signal without NiO shows a broad maximum of 6.5 ± 0.5 μV/K at 20 K. In the presence of NiO, the maximum shifts sharply to higher temperatures, likely correlated to the increase in decay length. This implies that NiO is most transparent to magnon propagation near the paramagnet-antiferromagnet transition. We do not see the enhancement in spin current driven into Pt reported in other papers when 1-2 nm NiO layers are sandwiched between Pt and YIG.

  16. Theory of spin transport in antiferromagnets (Conference Presentation)

    Science.gov (United States)

    Manchon, Aurélien; Saidaoui, Hamed; Akosa, Collins

    2016-10-01

    Antiferromagnets (AF) have long remained an intriguing and exotic state of matter, their application being restricted to enabling interfacial exchange bias in spin-valves. Their role in the expanding field of applied spintronics has been mostly passive and the in-depth investigation of their basic properties considered as fundamental condensed matter physics. A conceptual breakthrough was achieved ten years ago with the proposal that spin transfer torque could be used to electrically control the direction of the order parameter of AF spin valves, henceforth making these materials potential candidates for low energy spin devices. In spite of substantial theoretical efforts and experimental attempts to observe such a torque, the difficulty to independently detect the direction of the AF order parameter has remained a major obstacle. In this talk, I will first introduce the original concept of spin transfer torque in AF spin-valves, demonstrating that it is strongly limited by the spin decoherence and dramatically vanishes in the presence of disorder, leaving little hope to observe this effect experimentally. Then, I will present the newly proposed concept of spin-orbit torque that utilizes bulk or interfacial the spin-orbit coupling in non-centrosymmetric magnets to directly generate a torque on the AF order parameter. This torque, being local, is much more robust against impurities, as will be demonstrated for the specific case of interfacial Rashba spin-orbit coupling. Finally, I will discuss about spin motive force and torques in antiferromagnetic textures, intriguing effects that remained to be experimentally observed.

  17. Anisotropic Magnetoresistance in Antiferromagnetic Sr_{2}IrO_{4}

    Directory of Open Access Journals (Sweden)

    C. Wang

    2014-11-01

    Full Text Available We report point-contact measurements of anisotropic magnetoresistance (AMR in a single crystal of antiferromagnetic Mott insulator Sr_{2}IrO_{4}. The point-contact technique is used here as a local probe of magnetotransport properties on the nanoscale. The measurements at liquid nitrogen temperature reveal negative magnetoresistances (up to 28% for modest magnetic fields (250 mT applied within the IrO_{2} a-b plane and electric currents flowing perpendicular to the plane. The angular dependence of magnetoresistance shows a crossover from fourfold to twofold symmetry in response to an increasing magnetic field with angular variations in resistance from 1% to 14%. We tentatively attribute the fourfold symmetry to the crystalline component of AMR and the field-induced transition to the effects of applied field on the canting of antiferromagnetic-coupled moments in Sr_{2}IrO_{4}. The observed AMR is very large compared to the crystalline AMRs in 3d transition metal alloys or oxides (0.1%–0.5% and can be associated with the large spin-orbit interactions in this 5d oxide while the transition provides evidence of correlations between electronic transport, magnetic order, and orbital states. The finding of this work opens an entirely new avenue to not only gain a new insight into physics associated with spin-orbit coupling but also to better harness the power of spintronics in a more technically favorable fashion.

  18. The Heisenberg antiferromagnet on the square-kagomé lattice

    Directory of Open Access Journals (Sweden)

    J. Richter

    2009-01-01

    Full Text Available We discuss the ground state, the low-lying excitations as well as high-field thermodynamics of the Heisenberg antiferromagnet on the two-dimensional square-kagomé lattice. This magnetic system belongs to the class of highly frustrated spin systems with an infinite non-trivial degeneracy of the classical ground state as it is also known for the Heisenberg antiferromagnet on the kagomé and on the star lattice. The quantum ground state of the spin-half system is a quantum paramagnet with a finite spin gap and with a large number of non-magnetic excitations within this gap. We also discuss the magnetization versus field curve that shows a plateaux as well as a macroscopic magnetization jump to saturation due to independent localized magnon states. These localized states are highly degenerate and lead to interesting features in the low-temperature thermodynamics at high magnetic fields such as an additional low-temperature peak in the specific heat and an enhanced magnetocaloric effect.

  19. Three-sublattice skyrmion crystal in the antiferromagnetic triangular lattice

    Science.gov (United States)

    Rosales, H. D.; Cabra, D. C.; Pujol, Pierre

    2015-12-01

    The frustrated classical antiferromagnetic Heisenberg model with Dzyaloshinskii-Moriya (DM) interactions on the triangular lattice is studied under a magnetic field by means of semiclassical calculations and large-scale Monte Carlo simulations. We show that even a small DM interaction induces the formation of an antiferromagnetic skyrmion crystal (AF-SkX) state. Unlike what is observed in ferromagnetic materials, we show that the AF-SkX state consists of three interpenetrating skyrmion crystals (one by sublattice), and most importantly, the AF-SkX state seems to survive in the limit of zero temperature. To characterize the phase diagram we compute the average of the topological order parameter which can be associated with the number of topological charges or skyrmions. As the magnetic field increases this parameter presents a clear jump, indicating a discontinuous transition from a spiral phase into the AF-SkX phase, where multiple Bragg peaks coexist in the spin structure factor. For higher fields, a second (probably continuous) transition occurs into a featureless paramagnetic phase.

  20. Striped spin liquid crystal ground state instability of kagome antiferromagnets.

    Science.gov (United States)

    Clark, Bryan K; Kinder, Jesse M; Neuscamman, Eric; Chan, Garnet Kin-Lic; Lawler, Michael J

    2013-11-01

    The Dirac spin liquid ground state of the spin 1/2 Heisenberg kagome antiferromagnet has potential instabilities. This has been suggested as the reason why it does not emerge as the ground state in large-scale numerical calculations. However, previous attempts to observe these instabilities have failed. We report on the discovery of a projected BCS state with lower energy than the projected Dirac spin liquid state which provides new insight into the stability of the ground state of the kagome antiferromagnet. The new state has three remarkable features. First, it breaks spatial symmetry in an unusual way that may leave spinons deconfined along one direction. Second, it breaks the U(1) gauge symmetry down to Z(2). Third, it has the spatial symmetry of a previously proposed "monopole" suggesting that it is an instability of the Dirac spin liquid. The state described herein also shares a remarkable similarity to the distortion of the kagome lattice observed at low Zn concentrations in Zn-paratacamite and in recently grown single crystals of volborthite suggesting it may already be realized in these materials.

  1. Evidence for Intertwining of Superconductivity and Antiferromagnetism in a Cuprate

    Science.gov (United States)

    Tranquada, John; Xu, Zhijun; Stock, C.; Chi, S. X.; Kolesnikov, A. I.; Xu, G. Y.; Gu, G. D.

    2014-03-01

    We have used inelastic neutron scattering to measure the low-energy, incommensurate antiferromagnetic spin excitations both above and below the superconducting transition temperature (Tc = 32 K) of La1.905Ba0.095CuO4. While the magnetic excitations in optimally-doped cuprates typically show the development of a spin gap and magnetic resonance below Tc, our sample shows no such effect. Instead strong, gapless spin excitations coexist with bulk superconductivity. To understand this, we note that previous transport measurements have shown that the superconducting layers are decoupled by a magnetic field applied along the c-axis, resulting in a state with frustrated interlayer Josephson coupling, similar to LBCO with x = 1 / 8 , where it has been proposed that pair-density-wave superconductivity occurs. This suggests that, in a similar fashion, the spatially modulated antiferromagnetic correlations (which we see directly in the x = 0 . 095 sample) are intertwined with a spatially modulated superconducting pair wave function. Work at BNL supported by Office of Basic Energy Sciences, US DOE, under Contract No. DE-AC02-98CH10886.

  2. Low Field Magnetic and Thermal Hysteresis in Antiferromagnetic Dysprosium

    Directory of Open Access Journals (Sweden)

    Iuliia Liubimova

    2017-06-01

    Full Text Available Magnetic and thermal hysteresis (difference in magnetic properties on cooling and heating have been studied in polycrystalline Dy (dysprosium between 80 and 250 K using measurements of the reversible Villari effect and alternating current (AC susceptibility. We argue that measurement of the reversible Villari effect in the antiferromagnetic phase is a more sensitive method to detect magnetic hysteresis than the registration of conventional B(H loops. We found that the Villari point, recently reported in the antiferromagnetic phase of Dy at 166 K, controls the essential features of magnetic hysteresis and AC susceptibility on heating from the ferromagnetic state: (i thermal hysteresis in AC susceptibility and in the reversible Villari effect disappears abruptly at the temperature of the Villari point; (ii the imaginary part of AC susceptibility is strongly frequency dependent, but only up to the temperature of the Villari point; (iii the imaginary part of the susceptibility drops sharply also at the Villari point. We attribute these effects observed at the Villari point to the disappearance of the residual ferromagnetic phase. The strong influence of the Villari point on several magnetic properties allows this temperature to be ranked almost as important as the Curie and Néel temperatures in Dy and likely also for other rare earth elements and their alloys.

  3. Computational Electronic Structure of Antiferromagnetic Centers in Metalloproteins.

    Science.gov (United States)

    Rodriguez, Jorge H.

    2003-03-01

    Nature uses the properties of transition metal ions to carry out a variety of functions associated with vital life processes such as respiration and the transport of oxygen. Oxo-bridged diiron centers are intriguing structural motifs which are present in dioxygen transporting proteins and display antiferromagnetic ordering. We have performed a comprehensive study of the electronic structure and magnetic properties of structurally characterized models for diiron-oxo proteins. Results from Kohn-Sham density functional theory show that the models are antiferromagnetically coupled in agreement with experiment. The physical origin of the spin coupling has been elucidated as the main superexchange pathways responsible for magnetic ordering have been identified. In addition, the exchange constants that parameterize the Heisenberg Hamiltonian, H=JS_1.S_2, have been predicted in excellent agreement with experiment. Our results are important for establishing correlations between electronic structure and biomolecular function and show that computational electronic structure can be used as a powerful tool for the investigation of biomolecular magnetism.

  4. Thermally stable magnetic media based on antiferromagnetically coupled layers

    Science.gov (United States)

    Fullerton, Eric E.

    2001-03-01

    The combination of signal-to-noise requirements, write field limitations, and thermal activation of small particles is thought to limit the potential areal density of longitudinal media and is commonly referred to as the "superparamagnetic limit". Recording media composed of antiferromagnetically coupled (AFC) magnetic recording layers is a promising approach to extend areal densities of longitudinal media beyond these perceived limits [1,2]. The recording medium is made up of two ferromagnetic recording layer separated by a nonmagnetic layer whose thickness is tuned to couple the layers antiferromagnetically. For such a structure, the effective areal moment density (Mrt) of the composite structure is given by the difference between the ferromagnetic layers allowing the effective magnetic thickness to scale independently of the physical thickness of the media. The resulting media appears magnetically thin while being physically thick and, thus, allows AFC media to maintain thermal stability even for low Mrt values. Experimental realization of this concept using CoPtCrB alloy layers that demonstrates thermally stable low-Mrt media suitable for high-density recording will be discussed. This work is done in collaboration with D. T. Margulies, M. E. Schabes,M. Doerner, M. Carey, B. Gurney, A. Moser, M. Best, G. Zeltzer, K. Rubin, and H. Rosen. [1]. Fullerton et al., Appl. Phys. Lett. 77, 3806 (2000). [2]. Abarra et al., Appl. Phys. Lett. 77, 2581 (2000).

  5. Strain fields and electronic structure of antiferromagnetic CrN

    Science.gov (United States)

    Rojas, Tomas; Ulloa, Sergio E.

    2017-09-01

    We present a theoretical analysis of the role that strain plays on the electronic structure of chromium nitride (CrN) crystals. We use local spin-density approximation + U calculations to study the elastic constants, deformation potentials, and strain dependence of electron and hole masses near the fundamental gap. We consider the lowest energy antiferromagnetic models believed to describe CrN at low temperatures, and apply strain along different directions. We find relatively large deformation potentials for all models, and find increasing gaps for tensile strain along most directions. Most interestingly, we find that compressive strains should be able to close the relatively small indirect gap (≃100 meV) at moderate amplitudes ≃1.3 % . We also find large and anisotropic changes in the effective masses with strain, with principal axes closely related to the magnetic ordering of neighboring layers in the antiferromagnet. It would be interesting to consider the role that these effects may have on typical film growth on different substrates, and the possibility of monitoring optical and transport properties of thin films as strain is applied.

  6. The peak effect (PE) region of the antiferromagnetic two layer Ising nanographene

    Energy Technology Data Exchange (ETDEWEB)

    Şarlı, Numan, E-mail: numansarli82@gmail.com [Institute of Science, Erciyes University, 38039 Kayseri (Turkey); Akbudak, Salih [Department of Physics, Adiyaman University, 02100 Adiyaman (Turkey); Department of Nanotechnology and Nanomedicine, Hacettepe University, 06800 Ankara (Turkey); Ellialtıoğlu, Mehmet Recai [Department of Physics Engineering, Hacettepe University, 06800 Ankara (Turkey)

    2014-11-01

    In this work, the magnetic properties of the ferromagnetic and antiferromagnetic two layer spin-1/2 Ising nanographene systems are investigated within the effective field theory. We find that the magnetizations and the hysteresis behaviors of the central graphene atoms are similar to those of the edge graphene atoms in the ferromagnetic case. But, they are quite different in the antiferromagnetic case. The antiferromagnetic central graphene atoms exhibit type II superconductivity and they have triple hysteresis loop. The peak effect (PE) region is observed on the hysteresis curves of the antiferromagnetic Ising nanographene system. Therefore, we suggest that there is a strong relationship between the antiferromagnetism and the peak effect. Our results are in agreement with some experimental works in recent literature.

  7. Multi-stimuli manipulation of antiferromagnetic domains assessed by second-harmonic imaging

    Science.gov (United States)

    Chauleau, J.-Y.; Haltz, E.; Carrétéro, C.; Fusil, S.; Viret, M.

    2017-08-01

    Among the variety of magnetic textures available in nature, antiferromagnetism is one of the most `discrete' because of the exact cancellation of its staggered internal magnetization. It is therefore very challenging to probe. However, its insensitivity to external magnetic perturbations, together with the intrinsic sub-picosecond dynamics, make it very appealing for tomorrow's information technologies. Thus, it is essential to understand the microscopic mechanisms governing antiferromagnetic domains to achieve accurate manipulation and control. Using optical second-harmonic generation, a unique and laboratory-available tool, we succeeded in imaging with sub-micrometre resolution both electric and antiferromagnetic orders in the model multiferroic BiFeO3. We show here that antiferromagnetic domains can be manipulated with low power consumption, using sub-coercive electric fields and sub-picosecond light pulses. Interestingly, we also show that antiferromagnetic and ferroelectric domains can behave independently, thus revealing that magneto-electric coupling can lead to various arrangements of the two orders.

  8. Chiral Magnetic Effect and Anomalous Hall Effect in Antiferromagnetic Insulators with Spin-Orbit Coupling.

    Science.gov (United States)

    Sekine, Akihiko; Nomura, Kentaro

    2016-03-04

    We search for dynamical magnetoelectric phenomena in three-dimensional correlated systems with spin-orbit coupling. We focus on the antiferromagnetic insulator phases where the dynamical axion field is realized by the fluctuation of the antiferromagnetic order parameter. It is shown that the dynamical chiral magnetic effect, an alternating current generation by magnetic fields, emerges due to such time dependences of the order parameter as antiferromagnetic resonance. It is also shown that the anomalous Hall effect arises due to such spatial variations of the order parameter as antiferromagnetic domain walls. Our study indicates that spin excitations in antiferromagnetic insulators with spin-orbit coupling can result in nontrivial charge responses. Moreover, observing the chiral magnetic effect and anomalous Hall effect in our system is equivalent to detecting the dynamical axion field in condensed matter.

  9. Spin transfer torque in antiferromagnetic spin valves: From clean to disordered regimes

    KAUST Repository

    Saidaoui, Hamed Ben Mohamed

    2014-05-28

    Current-driven spin torques in metallic spin valves composed of antiferromagnets are theoretically studied using the nonequilibrium Green\\'s function method implemented on a tight-binding model. We focus our attention on G-type and L-type antiferromagnets in both clean and disordered regimes. In such structures, spin torques can either rotate the magnetic order parameter coherently (coherent torque) or compete with the internal antiferromagnetic exchange (exchange torque). We show that, depending on the symmetry of the spin valve, the coherent and exchange torques can either be in the plane, ∝n×(q×n) or out of the plane ∝n×q, where q and n are the directions of the order parameter of the polarizer and the free antiferromagnetic layers, respectively. Although disorder conserves the symmetry of the torques, it strongly reduces the torque magnitude, pointing out the need for momentum conservation to ensure strong spin torque in antiferromagnetic spin valves.

  10. Charge dynamics of the antiferromagnetically ordered Mott insulator

    Science.gov (United States)

    Han, Xing-Jie; Liu, Yu; Liu, Zhi-Yuan; Li, Xin; Chen, Jing; Liao, Hai-Jun; Xie, Zhi-Yuan; Normand, B.; Xiang, Tao

    2016-10-01

    We introduce a slave-fermion formulation in which to study the charge dynamics of the half-filled Hubbard model on the square lattice. In this description, the charge degrees of freedom are represented by fermionic holons and doublons and the Mott-insulating characteristics of the ground state are the consequence of holon-doublon bound-state formation. The bosonic spin degrees of freedom are described by the antiferromagnetic Heisenberg model, yielding long-ranged (Néel) magnetic order at zero temperature. Within this framework and in the self-consistent Born approximation, we perform systematic calculations of the average double occupancy, the electronic density of states, the spectral function and the optical conductivity. Qualitatively, our method reproduces the lower and upper Hubbard bands, the spectral-weight transfer into a coherent quasiparticle band at their lower edges and the renormalisation of the Mott gap, which is associated with holon-doublon binding, due to the interactions of both quasiparticle species with the magnons. The zeros of the Green function at the chemical potential give the Luttinger volume, the poles of the self-energy reflect the underlying quasiparticle dispersion with a spin-renormalised hopping parameter and the optical gap is directly related to the Mott gap. Quantitatively, the square-lattice Hubbard model is one of the best-characterised problems in correlated condensed matter and many numerical calculations, all with different strengths and weaknesses, exist with which to benchmark our approach. From the semi-quantitative accuracy of our results for all but the weakest interaction strengths, we conclude that a self-consistent treatment of the spin-fluctuation effects on the charge degrees of freedom captures all the essential physics of the antiferromagnetic Mott-Hubbard insulator. We remark in addition that an analytical approximation with these properties serves a vital function in developing a full understanding of the

  11. A model for ensemble NMR quantum computer using antiferromagnetic structure

    CERN Document Server

    Kokin, A A

    2000-01-01

    The one-dimensional homonuclear periodic array of nuclear spins I = 1/2,owing to hyperfine interaction of nuclear spins with electronic magneticmoments in antiferromagnetic structure, is considered. The neighbor nuclearspins in such array are opposite oriented and have resonant frequenciesdetermined by hyperfine interaction constant, applied magnetic field value andinteraction with the left and right nuclear neighbor spins. The resonantfrequencies difference of nuclear spins, when the neighbor spins have differentand the same states, is used to control the spin dynamics by means of selectiveresonant RF-pulses both for single nuclear spins and for ensemble of nuclearspins with the same resonant frequency. A model for the NMR quantum computer of cellular-automata type based on anone-dimensional homonuclear periodic array of spins is proposed. This model maybe generalized to a large ensemble of parallel working one-dimensional arraysand to two-dimensional and three-dimensional structures.

  12. Magnetocaloric properties of a frustrated Blume-Capel antiferromagnet

    Directory of Open Access Journals (Sweden)

    Žukovič Milan

    2014-07-01

    Full Text Available Low-temperature magnetization processes and magnetocaloric properties of a geometrically frustrated spin-1 Blume-Capel model on a triangular lattice are studied by Monte Carlo simulations. The model is found to display qualitatively different behavior depending on the sign of the single-ion anisotropy D. For positive values of D we observe two magnetization plateaus, similar to the spin-1/2 Ising antiferromagnet, and negative isothermal entropy changes for any field intensity. For a range of small negative values of D there are four magnetization plateaus and the entropy changes can be either negative or positive, depending on the field. If D is negative but large in absolute value then the entropy changes are solely positive.

  13. Terahertz-Driven Nonlinear Spin Response of Antiferromagnetic Nickel Oxide

    Science.gov (United States)

    Baierl, S.; Mentink, J. H.; Hohenleutner, M.; Braun, L.; Do, T.-M.; Lange, C.; Sell, A.; Fiebig, M.; Woltersdorf, G.; Kampfrath, T.; Huber, R.

    2016-11-01

    Terahertz magnetic fields with amplitudes of up to 0.4 Tesla drive magnon resonances in nickel oxide while the induced dynamics is recorded by femtosecond magneto-optical probing. We observe distinct spin-mediated optical nonlinearities, including oscillations at the second harmonic of the 1 THz magnon mode. The latter originate from coherent dynamics of the longitudinal component of the antiferromagnetic order parameter, which are probed by magneto-optical effects of second order in the spin deflection. These observations allow us to dynamically disentangle electronic from lattice-related contributions to magnetic linear birefringence and dichroism—information so far only accessible by ultrafast THz spin control. The nonlinearities discussed here foreshadow physics that will become essential in future subcycle spin switching.

  14. Space Group Symmetry Fractionalization in a Chiral Kagome Heisenberg Antiferromagnet.

    Science.gov (United States)

    Zaletel, Michael P; Zhu, Zhenyue; Lu, Yuan-Ming; Vishwanath, Ashvin; White, Steven R

    2016-05-13

    The anyonic excitations of a spin liquid can feature fractional quantum numbers under space group symmetries. Detecting these fractional quantum numbers, which are analogs of the fractional charge of Laughlin quasiparticles, may prove easier than the direct observation of anyonic braiding and statistics. Motivated by the recent numerical discovery of spin-liquid phases in the kagome Heisenberg antiferromagnet, we theoretically predict the pattern of space group symmetry fractionalization in the kagome lattice SO(3)-symmetric chiral spin liquid. We provide a method to detect these fractional quantum numbers in finite-size numerics which is simple to implement in the density matrix renormalization group. Applying these developments to the chiral spin liquid phase of a kagome Heisenberg model, we find perfect agreement between our theoretical prediction and numerical observations.

  15. Calculation of nonlinear magnetic susceptibility tensors for a uniaxial antiferromagnet

    Science.gov (United States)

    Lim, Siew-Choo; Osman, Junaidah; Tilley, D. R.

    2000-11-01

    In this paper, we present a derivation of the nonlinear susceptibility tensors for a two-sublattice uniaxial antiferromagnet up to the third-order effects within the standard definition by which the rf magnetization m is defined as a power series expansion in the rf fields h with the susceptibility tensors χ(q) as the coefficients. The starting point is the standard set of torque equations of motion for this problem. A complete set of tensor elements is derived for the case of a single-frequency input wave. Within a circular polarization frame (pnz) expressions are given for the first-order susceptibility, second-harmonic generation, optical rectification, third-harmonic generation and intensity-dependent susceptibility. Some of the coefficients with representative resonance features in the far infrared are illustrated graphically and we conclude with a brief discussion of the implications of the resonance features arising from the calculations and their potential applications.

  16. Magnetoelastic properties of antiferromagnetically coupled magnetic composite media

    Science.gov (United States)

    Valencia-Cardona, Juan J.; Leo, Perry H.

    2016-08-01

    We study the magnetic response of a ferromagnetic bilayer with antiferromagnetic coupling, where the layers experience magnetostrictive strains and epitaxial misfit strains. These strains cause the layers to stretch and bend as the magnetic spins of the layers rotate, resulting in elastic energy that adds to the magnetic energy of the system. The magnetic and elastic energies are computed as a function of spin direction in each layer for a given set of material and geometric parameters. By finding the rotations that minimize the total energy, we compute magnetic hysteresis loops for different combinations of magnetic and elastic parameters. The elastic contribution is reflected in the transitions at the corners of the hysteresis curves as well as in the coercive field of the main loop. The details of the elastic contribution depend in a complicated way on the magnetostriction of the layers, the epitaxial strain, the magnetic anisotropies, and the system geometry.

  17. Ferrimagnetism in delta chain with anisotropic ferromagnetic and antiferromagnetic interactions

    Science.gov (United States)

    Dmitriev, D. V.; Krivnov, V. Ya

    2016-12-01

    We consider analytically and numerically an anisotropic spin-\\frac{1}{2} delta-chain (sawtooth chain) in which exchange interactions between apical and basal spins are ferromagnetic and those between basal spins are antiferromagnetic. In the limit of strong anisotropy of exchange interactions this model can be considered as the Ising delta chain with macroscopic degenerate ground state perturbed by transverse quantum fluctuations. These perturbations lift the ground state degeneracy and the model reduces to the basal XXZ spin chain in the magnetic field induced by static apical spins. We show that the ground state of such a model is ferrimagnetic. The excitations of the model are formed by ferrimagnetic domains separated by domain walls with a finite energy. At low temperatures the system is effectively divided into two independent subsystems, the apical subsystem described by the Ising spin-\\frac{1}{2} chain and the basal subsystem described by the XXZ chain with infinite zz interactions.

  18. Ab initio dynamical exchange interactions in frustrated antiferromagnets

    Science.gov (United States)

    Simoni, Jacopo; Stamenova, Maria; Sanvito, Stefano

    2017-08-01

    The ultrafast response to an optical pulse excitation of the spin-spin exchange interaction in transition metal antiferromagnets is studied within the framework of the time-dependent spin-density functional theory. We propose a formulation for the full dynamical exchange interaction, which is nonlocal in space, and it is derived starting from ab initio arguments. Then, we investigate the effect of the laser pulse on the onset of the dynamical process. It is found that we can distinguish two types of excitations, both activated immediately after the action of the laser pulse. While the first one can be associated to a Stoner-like excitation and involves the transfer of spin from one site to another, the second one is related to the ultrafast modification of a Heisenberg-like exchange interaction and can trigger the formation of spin waves in the first few hundred femtoseconds of the time evolution.

  19. Interfaces in superconducting hybrid heterostructures with an antiferromagnetic interlayer

    Science.gov (United States)

    Constantinian, K. Y.; Kislinskii, Yu. V.; Ovsyannikov, G. A.; Shadrin, A. V.; Sheyerman, A. E.; Vasil'ev, A. L.; Presnyakov, M. Yu.; Komissinskiy, P. V.

    2013-03-01

    The structural, X-ray diffraction, and electrophysical studies of hybrid superconducting hetero-structures with an interlayer of cuprate antiferromagnetic Ca1 - x Sr x CuO2 (CSCO) with the upper electrode Nb/Au and the lower electrode YBa2Cu3O7 - δ (YBCO) have been carried out. It has been experimentally shown that the epitaxial growth of two cuprates, YBCO and CSCO, results in the formation of an interface on which the enrichment of the CSCO interlayer with charge carriers proceeds to a depth of about 20 nm. In this case, the conduction of the enriched CSCO region proves to be closer to metallic, whereas the CSCO film deposited onto the NdGaO3 substrate is a Mott insulator with hopping conduction.

  20. Performance of synthetic antiferromagnetic racetrack memory: domain wall versus skyrmion

    Science.gov (United States)

    Tomasello, R.; Puliafito, V.; Martinez, E.; Manchon, A.; Ricci, M.; Carpentieri, M.; Finocchio, G.

    2017-08-01

    A storage scheme based on racetrack memory, where the information can be coded in a domain or a skyrmion, seems to be an alternative to conventional hard disk drive for high density storage. Here, we perform a full micromagnetic study of the performance of synthetic antiferromagnetic (SAF) racetrack memory in terms of velocity and sensitivity to defects by using experimental parameters. We find that, to stabilize a SAF skyrmion, the Dzyaloshinskii-Moriya interaction in the top and the bottom ferromagnet should have an opposite sign. The velocity of SAF skyrmions and SAF Néel domain walls are of the same order and can reach values larger than 1200 m s-1 if a spin-orbit torque from the spin-Hall effect with opposite sign is applied to both ferromagnets. The presence of disordered anisotropy in the form of randomly distributed grains introduces a threshold current for both SAF skyrmions and SAF domain walls motions.

  1. Antiferromagnetic topological superconductor and electrically controllable Majorana fermions.

    Science.gov (United States)

    Ezawa, Motohiko

    2015-02-01

    We investigate the realization of a topological superconductor in a generic bucked honeycomb system equipped with four types of mass-generating terms, where the superconductor gap is introduced by attaching the honeycomb system to an s-wave superconductor. Constructing the topological phase diagram, we show that Majorana modes are formed in the phase boundary. In particular, we analyze the honeycomb system with antiferromagnetic order in the presence of perpendicular electric field E(z). It becomes topological for |E(z)|>E(z)(cr) and trivial for |E(z)|superconductor by controlling applied electric field. One Majorana zero-energy bound state appears at the phase boundary. We can arbitrarily control the position of the Majorana fermion by moving the spot of applied electric field, which will be made possible by a scanning tunneling microscope probe.

  2. Barlowite as a canted antiferromagnet: Theory and experiment

    Science.gov (United States)

    Jeschke, Harald O.; Salvat-Pujol, Francesc; Gati, Elena; Hoang, Nguyen Hieu; Wolf, Bernd; Lang, Michael; Schlueter, John A.; Valentí, Roser

    2015-09-01

    We investigate the structural, electronic, and magnetic properties of the newly synthesized mineral barlowite Cu4(OH) 6FBr which contains Cu2 + ions in a perfect kagome arrangement. In contrast to the spin-liquid candidate herbertsmithite ZnCu3(OH)6Cl 2, kagome layers in barlowite are perfectly aligned due to the different bonding environments adopted by F- and Br- compared to Cl-. With the synthesis of this material we unveil a design strategy for layered kagome systems with possible exotic magnetic states. Density functional theory calculations and effective model considerations for Cu4(OH) 6FBr , which has a Cu2 + site coupling the kagome layers, predict a three-dimensional network of exchange couplings, which together with a substantial Dzyaloshinskii-Moriya coupling lead to canted antiferromagnetic ordering of this compound in excellent agreement with magnetic susceptibility measurements on single crystals yielding TN=15 K .

  3. Antiferromagnetic Ising model in an imaginary magnetic field

    Science.gov (United States)

    Azcoiti, Vicente; Di Carlo, Giuseppe; Follana, Eduardo; Royo-Amondarain, Eduardo

    2017-09-01

    We study the two-dimensional antiferromagnetic Ising model with a purely imaginary magnetic field, which can be thought of as a toy model for the usual θ physics. Our motivation is to have a benchmark calculation in a system which suffers from a strong sign problem, so that our results can be used to test Monte Carlo methods developed to tackle such problems. We analyze here this model by means of analytical techniques, computing exactly the first eight cumulants of the expansion of the effective Hamiltonian in powers of the inverse temperature, and calculating physical observables for a large number of degrees of freedom with the help of standard multiprecision algorithms. We report accurate results for the free energy density, internal energy, standard and staggered magnetization, and the position and nature of the critical line, which confirm the mean-field qualitative picture, and which should be quantitatively reliable, at least in the high-temperature regime, including the entire critical line.

  4. Impurities near an antiferromagnetic-singlet quantum critical point

    Science.gov (United States)

    Mendes-Santos, T.; Costa, N. C.; Batrouni, G.; Curro, N.; dos Santos, R. R.; Paiva, T.; Scalettar, R. T.

    2017-02-01

    Heavy-fermion systems and other strongly correlated electron materials often exhibit a competition between antiferromagnetic (AF) and singlet ground states. Using exact quantum Monte Carlo simulations, we examine the effect of impurities in the vicinity of such an AF-singlet quantum critical point (QCP), through an appropriately defined "impurity susceptibility" χimp. Our key finding is a connection within a single calculational framework between AF domains induced on the singlet side of the transition and the behavior of the nuclear magnetic resonance (NMR) relaxation rate 1 /T1 . We show that local NMR measurements provide a diagnostic for the location of the QCP, which agrees remarkably well with the vanishing of the AF order parameter and large values of χimp.

  5. Performance of synthetic antiferromagnetic racetrack memory: domain wall versus skyrmion

    KAUST Repository

    Tomasello, R

    2017-06-20

    A storage scheme based on racetrack memory, where the information can be coded in a domain or a skyrmion, seems to be an alternative to conventional hard disk drive for high density storage. Here, we perform a full micromagnetic study of the performance of synthetic antiferromagnetic (SAF) racetrack memory in terms of velocity and sensitivity to defects by using experimental parameters. We find that, to stabilize a SAF skyrmion, the Dzyaloshinskii–Moriya interaction in the top and the bottom ferromagnet should have an opposite sign. The velocity of SAF skyrmions and SAF Néel domain walls are of the same order and can reach values larger than 1200 m s−1 if a spin–orbit torque from the spin-Hall effect with opposite sign is applied to both ferromagnets. The presence of disordered anisotropy in the form of randomly distributed grains introduces a threshold current for both SAF skyrmions and SAF domain walls motions.

  6. New heavy-fermion antiferromagnet UPd2Cd20

    Science.gov (United States)

    Hirose, Yusuke; Doto, Hiroshi; Honda, Fuminori; Li, Dexin; Aoki, Dai; Haga, Yoshinori; Settai, Rikio

    2016-10-01

    We succeeded in growing a new high quality single crystal of a ternary uranium compound UPd2Cd20. From the electrical resistivity, magnetization, magnetic susceptibility, and specific heat experiments, UPd2Cd20 is found to be an antiferromagnetic heavy-fermion compound with the Néel temperature {{T}\\text{N}}   =  5 K and exhibits the large electronic specific heat coefficient γ exceeding 500 mJ (K2· mol)-1. This compound is the first one that exhibits the magnetic ordering with the magnetic moments of the U atom in a series of UT2X20 (T: transition metal, X  =  Al, Zn, Cd). UPd2Cd20 shows typical characteristic features in heavy-fermion systems such as a broad maximum in the magnetic susceptibility at {{T}{{χ\\text{max}}}} and a large coefficient A of T 2 term in the resistivity.

  7. Magnetic Orders and Fluctuations in the Dipolar Pyrochlore Antiferromagnet

    Science.gov (United States)

    Cepas, Olivier; Shastry, B. Sriram

    2005-03-01

    While the classical Heisenberg antiferromagnet on the pyrochlore lattice does not order, we will discuss, from a theoretical standpoint, possible magnetic phases induced by the dipole-dipole interactions. Such interactions play a role in systems such as Gd2Ti2O7 or Gd2Sn2O7 in stabilizing exotic forms of magnetic order, a subject of current debate. We will also argue that the external magnetic field induces multiple transitions, one of which is associated with no obvious broken symmetry, but can be characterized by a disorder parameter. Finally, Monte-Carlo simulations and Landau-Ginzburg expansion show that the dipolar Heisenberg model exhibits a fluctuation-induced first-order transition, thanks to the frustration and a continuous set of soft modes.

  8. Potassium tantalate substrates for neutron experiments on antiferromagnetic perovskite films

    Energy Technology Data Exchange (ETDEWEB)

    Christen, H M; MacDougall, G J; Kim, H-S; Kim, D H; Boatner, L A; Bennett, C J Callender; Zarestky, J L; Nagler, S E, E-mail: christenhm@ornl.gov

    2010-11-01

    For the study of antiferromagnetism in thin-film materials, neutron diffraction is a particularly important tool, especially since magnetometry experiments are often complicated by the substrate's strong diamagnetic or paramagnetic contribution. However, the substrate, by necessity, has a lattice parameter that is very similar to that of the film, and in most cases is over 1000 times more massive than the film. Therefore, even weak structural distortions in the substrate crystal may complicate the analysis of magnetic scattering from the film. Here we show that in contrast to most other perovskite substrates (including SrTiO{sub 3}, LaAlO{sub 3}, etc.), KTaO3 provides a uniquely appropriate substrate platform for magnetic diffraction experiments on epitaxial oxide films.

  9. Half-metallic antiferromagnet as a prospective material for spintronics.

    Science.gov (United States)

    Hu, X

    2012-01-10

    Spintronics is expected as the next-generation technology based on the novel notch of spin degree of freedom of electrons. Half-metals, a class of materials which behave as a metal in one spin direction and an insulator in the opposite spin direction, are ideal for spintronic applications. Half-metallic antiferromagnets as a subclass of half-metals are characterized further by totally compensated spin moments in a unit cell, and have the advantage of being able to generate fully spin-polarized current while exhibiting zero macroscopic magnetization. Considerable efforts have been devoted to the search for this novel material, from which we may get useful insights for prospective material exploration.

  10. Quantum Phase Transitions in Anti-ferromagnetic Planar Cubic Lattices

    CERN Document Server

    Wellard, C J; Wellard, Cameron; Orus, Roman

    2004-01-01

    Motivated by its relation to an NP-hard problem we analyze the ground state properties of anti-ferromagnetic Ising-spin networks in planar cubic lattices under the action of homogeneous transverse and longitudinal magnetic fields. We consider different instances of the cubic geometry and find a set of quantum phase transitions for each one of the systems, which we characterize by means of entanglement behavior and majorization theory. Entanglement scaling at the critical region is in agreement with results arising from conformal symmetry, therefore even the simplest planar systems can display very large amounts of quantum correlation. No conclusion can be made as to the scaling behavior of the minimum energy gap, with the data allowing equally good fits to exponential and power law decays. Analysis of entanglement and especially of majorization instead of the energy spectrum proves to be a good way of detecting quantum phase transitions in highly frustrated configurations.

  11. Spectral evolution with doping of an antiferromagnetic Mott state

    Science.gov (United States)

    Wu, Huan-Kuang; Lee, Ting-Kuo

    2017-01-01

    Since the discovery of half-filled cuprate to be a Mott insulator, the excitation spectra above the chemical potential for the unoccupied states has attracted much research attention. There were many theoretical works using different numerical techniques to study this problem, but many have reached different conclusions. One of the reasons is the lack of very detailed high-resolution experimental results for the theories to be compared with. Recently, the scanning tunneling spectroscopy [P. Cai et al., Nat. Phys. 12, 1047 (2016), 10.1038/nphys3840; C. Ye et al., Nat. Commun. 4, 1365 (2013), 10.1038/ncomms2369] on lightly doped Mott insulator with an antiferromagnetic order found the presence of in-gap states with energy of order half an eV above the chemical potential. The measured spectral properties with doping are not quite consistent with earlier theoretical works. Although the experiment has disorder and localization effect, but for the energy scale we will study here, a model without disorder is sufficed to illustrate the underlying physics. We perform a diagonalization method on top of the variational Monte Carlo calculation to study the evolution of antiferromagnetic Mott state with doped hole concentration in the Hubbard model. Our results found in-gap states that behave similarly with ones reported by STS. These in-gap states acquire a substantial amount of dynamical spectral weight transferred from the upper Hubbard band. The in-gap states move toward chemical potential with increasing spectral weight as doping increases. Our result also provides information about the energy scale of these in-gap states in relation with the Coulomb coupling strength U .

  12. Spin-wave multiple excitations in nanoscale classical Heisenberg antiferromagnets

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Zhuofei [University of Georgia, Athens; Landau, David P [University of Georgia, Athens; Stocks, George Malcolm [ORNL; Brown, G. [Florida State University, Tallahassee

    2015-02-17

    Monte Carlo and spin dynamics techniques have been used to perform large-scale simulations of the dynamic behavior of a nanoscale, classical, Heisenberg antiferromagnet on a simple-cubic lattice with linear sizes L≤ 40 at a temperature below the Neel temperature. In this study, nanoparticles are modeled with completely free boundary conditions, i.e., six free surfaces, and nanofilms are modeled with two free surfaces in the spatial z direction and periodic boundaries parallel to the surfaces in the xy direction, which are compared to the infinite system with periodic boundary conditions. The temporal evolutions of spin configurations were determined numerically from coupled equations of motion for individual spins using a fast spin dynamics algorithm with the fourth-order Suzuki-Trotter decomposition of exponential operators, with initial spin configurations generated by Monte Carlo simulations. The local dynamic structure factor S(q,ω) was calculated from the local space- and time-displaced spin-spin correlation function. Multiple excitation peaks for wave vectors within the first Brillouin zone appear in the spin-wave spectra of the transverse component of dynamic structure factor ST (q,ω) in the nanoscale classical Heisenberg antiferromagnet, which are lacking if periodic boundary conditions are used. With the assumption of q-space spin-wave reflections with broken momentum conservation due to free-surface confinements, we successfully explained those spectra quantitatively in the linear dispersion region. Meanwhile, we also observed two unexpected quantized spin-wave excitation modes in the spatial z direction in nanofilms for ST (q,ω) not expected in bulk systems. In conclusion, the results of this study indicate the presence of unexpected forms of spin-wave excitation behavior that have yet to be observed experimentally but could be directly tested through neutron scattering experiments on nanoscale RbMnF3 particles or

  13. Magnetic correlations and quantum criticality in the insulating antiferromagnetic, insulating spin liquid, renormalized Fermi liquid, and metallic antiferromagnetic phases of the Mott system V2O3

    Science.gov (United States)

    Bao, Wei; Broholm, C.; Aeppli, G.; Carter, S. A.; Dai, P.; Rosenbaum, T. F.; Honig, J. M.; Metcalf, P.; Trevino, S. F.

    1998-11-01

    Magnetic correlations in all four phases of pure and doped vanadium sesquioxide (V2O3) have been examined by magnetic thermal-neutron scattering. Specifically, we have studied the antiferromagnetic and paramagnetic phases of metallic V2-yO3, the antiferromagnetic insulating and paramagnetic metallic phases of stoichiometric V2O3, and the antiferromagnetic and paramagnetic phases of insulating V1.944Cr0.056O3. While the antiferromagnetic insulator can be accounted for by a localized Heisenberg spin model, the long-range order in the antiferromagnetic metal is an incommensurate spin-density wave, resulting from a Fermi surface nesting instability. Spin dynamics in the strongly correlated metal are dominated by spin fluctuations with a ``single lobe'' spectrum in the Stoner electron-hole continuum. Furthermore, our results in metallic V2O3 represent an unprecedentedly complete characterization of the spin fluctuations near a metallic quantum critical point, and provide quantitative support for the self-consistent renormalization theory for itinerant antiferromagnets in the small moment limit. Dynamic magnetic correlations for ħωantiferromagnetic insulator, from the paramagnetic metal and the paramagnetic insulator, introduces a sudden switching of magnetic correlations to a different spatial periodicity which indicates a sudden change in the underlying spin Hamiltonian. To describe this phase transition and also the unusual short-range order in the paramagnetic state, it seems necessary to take into account the orbital degrees of freedom associated with the degenerate d orbitals at the Fermi level in V2O3.

  14. Effect of antiferromagnetic layer thickness on exchange bias, training effect, and magnetotransport properties in ferromagnetic/antiferromagnetic antidot arrays

    Energy Technology Data Exchange (ETDEWEB)

    Gong, W. J.; Liu, W., E-mail: wliu@imr.ac.cn; Feng, J. N.; Zhang, Z. D. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Kim, D. S.; Choi, C. J. [Functional Materials Division, Korea Institute of Materials Science, 531 Changwon- daero, Changwon 631-831 (Korea, Republic of)

    2014-04-07

    The effect of antiferromagnetic (AFM) layer on exchange bias (EB), training effect, and magnetotransport properties in ferromagnetic (FM) /AFM nanoscale antidot arrays and sheet films Ag(10 nm)/Co(8 nm)/NiO(t{sub NiO})/Ag(5 nm) at 10 K is studied. The AFM layer thickness dependence of the EB field shows a peak at t{sub NiO} = 2 nm that is explained by using the random field model. The misalignment of magnetic moments in the three-dimensional antidot arrays causes smaller decrease of EB field compared with that in the sheet films for training effect. The anomalous magnetotransport properties, in particular positive magnetoresistance (MR) for antidot arrays but negative MR for sheet films are found. The training effect and magnetotransport properties are strongly affected by the three-dimensional spin-alignment effects in the antidot arrays.

  15. Imaging Current-Induced Switching of Antiferromagnetic Domains in CuMnAs

    Science.gov (United States)

    Grzybowski, M. J.; Wadley, P.; Edmonds, K. W.; Beardsley, R.; Hills, V.; Campion, R. P.; Gallagher, B. L.; Chauhan, J. S.; Novak, V.; Jungwirth, T.; Maccherozzi, F.; Dhesi, S. S.

    2017-02-01

    The magnetic order in antiferromagnetic materials is hard to control with external magnetic fields. Using x-ray magnetic linear dichroism microscopy, we show that staggered effective fields generated by electrical current can induce modification of the antiferromagnetic domain structure in microdevices fabricated from a tetragonal CuMnAs thin film. A clear correlation between the average domain orientation and the anisotropy of the electrical resistance is demonstrated, with both showing reproducible switching in response to orthogonally applied current pulses. However, the behavior is inhomogeneous at the submicron level, highlighting the complex nature of the switching process in multidomain antiferromagnetic films.

  16. Ultrafast spin dynamics and switching via spin transfer torque in antiferromagnets with weak ferromagnetism

    Science.gov (United States)

    Kim, Tae Heon; Grünberg, Peter; Han, Song Hee; Cho, Beongki

    2016-10-01

    The spin-torque driven dynamics of antiferromagnets with Dzyaloshinskii-Moriya interaction (DMI) were investigated based on the Landau-Lifshitz-Gilbert-Slonczewski equation with antiferromagnetic and ferromagnetic order parameters (l and m, respectively). We demonstrate that antiferromagnets including DMI can be described by a 2-dimensional pendulum model of l. Because m is coupled with l, together with DMI and exchange energy, close examination of m provides fundamental understanding of its dynamics in linear and nonlinear regimes. Furthermore, we discuss magnetization reversal as a function of DMI and anisotropy energy induced by a spin current pulse.

  17. Long-range order for the spin-1 Heisenberg model with a small antiferromagnetic interaction

    Energy Technology Data Exchange (ETDEWEB)

    Lees, Benjamin, E-mail: b.lees@warwick.ac.uk [Department of Mathematics, University of Warwick, Coventry CV4 7AL (United Kingdom)

    2014-09-15

    We look at the general SU(2) invariant spin-1 Heisenberg model. This family includes the well-known Heisenberg ferromagnet and antiferromagnet as well as the interesting nematic (biquadratic) and the largely mysterious staggered-nematic interaction. Long range order is proved using the method of reflection positivity and infrared bounds on a purely nematic interaction. This is achieved through the use of a type of matrix representation of the interaction making clear several identities that would not otherwise be noticed. Using the reflection positivity of the antiferromagnetic interaction one can then show that the result is maintained if we also include an antiferromagnetic interaction that is sufficiently small.

  18. Ultrafast spin dynamics and switching via spin transfer torque in antiferromagnets with weak ferromagnetism

    Science.gov (United States)

    Kim, Tae Heon; Grünberg, Peter; Han, Song Hee; Cho, Beongki

    2016-01-01

    The spin-torque driven dynamics of antiferromagnets with Dzyaloshinskii-Moriya interaction (DMI) were investigated based on the Landau-Lifshitz-Gilbert-Slonczewski equation with antiferromagnetic and ferromagnetic order parameters (l and m, respectively). We demonstrate that antiferromagnets including DMI can be described by a 2-dimensional pendulum model of l. Because m is coupled with l, together with DMI and exchange energy, close examination of m provides fundamental understanding of its dynamics in linear and nonlinear regimes. Furthermore, we discuss magnetization reversal as a function of DMI and anisotropy energy induced by a spin current pulse. PMID:27713522

  19. Observation of the antiferromagnetic resonance of multi-sublattice modes in KCuF 3

    Science.gov (United States)

    Shi, Qingfan; Li, Liangsheng; Mino, Michinobu; Yamada, Isao; Yamazaki, Hitoshi

    2006-05-01

    We report antiferromagnetic resonance measurements of KCuF 3 at various frequencies from 3.8 to 10 GHz at 4.2 K. A second antiferromagnetic resonance absorption mode is observed in the [1 0 0] p direction and equivalent directions, where [ ] p represents an axis in a unit cell of the perovskite structure. Using the eight-sublattice model proposed by Yamada and Kato [J. Phys. Soc. Japan 63 (1994) 289], the numerical calculation for the antiferromagnetic resonance indicates that this second absorption mode comes from one of the resonance modes of the eight-sublattice system.

  20. Superfluid and antiferromagnetic phases in ultracold fermionic quantum gases

    Energy Technology Data Exchange (ETDEWEB)

    Gottwald, Tobias

    2010-08-27

    In this thesis several models are treated, which are relevant for ultracold fermionic quantum gases loaded onto optical lattices. In particular, imbalanced superfluid Fermi mixtures, which are considered as the best way to realize Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) states experimentally, and antiferromagnetic states, whose experimental realization is one of the next major goals, are examined analytically and numerically with the use of appropriate versions of the Hubbard model. The usual Bardeen-Cooper-Schrieffer (BCS) superconductor is known to break down in a magnetic field with a strength exceeding the size of the superfluid gap. A spatially inhomogeneous spin-imbalanced superconductor with a complex order parameter known as FFLO-state is predicted to occur in translationally invariant systems. Since in ultracold quantum gases the experimental setups have a limited size and a trapping potential, we analyze the realistic situation of a non-translationally invariant finite sized Hubbard model for this purpose. We first argue analytically, why the order parameter should be real in a system with continuous coordinates, and map our statements onto the Hubbard model with discrete coordinates defined on a lattice. The relevant Hubbard model is then treated numerically within mean field theory. We show that the numerical results agree with our analytically derived statements and we simulate various experimentally relevant systems in this thesis. Analogous calculations are presented for the situation at repulsive interaction strength where the N'eel state is expected to be realized experimentally in the near future. We map our analytical results obtained for the attractive model onto corresponding results for the repulsive model. We obtain a spatially invariant unit vector defining the direction of the order parameter as a consequence of the trapping potential, which is affirmed by our mean field numerical results for the repulsive case. Furthermore, we observe

  1. Evaluation of Watson-like integrals for a hyper bcc antiferromagnetic lattice

    Science.gov (United States)

    Radošević, S. M.; Pantić, M. R.; Kapor, D. V.; Pavkov-Hrvojević, M. V.; Škrinjar, M. G.

    2010-04-01

    Watson-like integrals for a d-dimensional bcc antiferromagnetic lattice, I_d (\\eta ) =\\frac{1}{\\pi ^d} \\prod _{i = 1}^d \\int _0^{\\pi } \\mathrm{d}x_i \\; \\frac{ \\eta }{\\sqrt{\\eta ^2 - \\prod \

  2. Tetragonal phase of epitaxial room-temperature antiferromagnet CuMnAs.

    Science.gov (United States)

    Wadley, P; Novák, V; Campion, R P; Rinaldi, C; Martí, X; Reichlová, H; Zelezný, J; Gazquez, J; Roldan, M A; Varela, M; Khalyavin, D; Langridge, S; Kriegner, D; Máca, F; Mašek, J; Bertacco, R; Holý, V; Rushforth, A W; Edmonds, K W; Gallagher, B L; Foxon, C T; Wunderlich, J; Jungwirth, T

    2013-01-01

    Recent studies have demonstrated the potential of antiferromagnets as the active component in spintronic devices. This is in contrast to their current passive role as pinning layers in hard disk read heads and magnetic memories. Here we report the epitaxial growth of a new high-temperature antiferromagnetic material, tetragonal CuMnAs, which exhibits excellent crystal quality, chemical order and compatibility with existing semiconductor technologies. We demonstrate its growth on the III-V semiconductors GaAs and GaP, and show that the structure is also lattice matched to Si. Neutron diffraction shows collinear antiferromagnetic order with a high Néel temperature. Combined with our demonstration of room-temperature-exchange coupling in a CuMnAs/Fe bilayer, we conclude that tetragonal CuMnAs films are suitable candidate materials for antiferromagnetic spintronics.

  3. The magnetoelectric properties study for system with the coexistence of the ferroelectric and antiferromagnetic orders

    Energy Technology Data Exchange (ETDEWEB)

    Jiang Qing; Zhong Chonggui

    2002-12-30

    Soft-mode theory based on DIFFOUR model for ferroelectric interaction and the mean-field theory of high spin Ising model for antiferromagnetic interaction are used to investigate the ferroelectric, antiferromagnetic, magnetoelectric properties in ferroelectromagnetic lattice in which the ferroelectric order and antiferromagnetic order coexist simultaneously below a certain temperature. Ferroelectric polarization, spin moment, and magnetoelectric susceptibility as well, as a function of temperature for system, are calculated and compared with the different coupling coefficient. It is found that an anomaly appears in curve of the polarization susceptibility as a function of temperature due to the coupling between the ferroelectric and antiferromagnetic orders in the ferroelectromagnetic lattice. At the same time, we also considered the influence of magnetoelectric effect on polarization susceptibility by applying the external field including electric and magnetic.

  4. Thickness-dependent cooperative aging in polycrystalline films of antiferromagnet CoO

    Science.gov (United States)

    Ma, Tianyu; Cheng, Xiang; Boettcher, Stefan; Urazhdin, Sergei; Novozhilova, Lydia

    2016-07-01

    We demonstrate that thin polycrystalline films of antiferromagnet CoO, in bilayers with ferromagnetic Permalloy, exhibit slow power-law aging of their magnetization state. The aging characteristics are remarkably similar to those previously observed in thin epitaxial Fe50Mn50 films, indicating that these behaviors are likely generic to ferromagnet/antiferromagnet bilayers. In very thin films, aging is observed over a wide temperature range. In thicker CoO, aging effects become reduced at low temperatures. Aging entirely disappears for large CoO thicknesses. We also investigate the dependence of aging characteristics on temperature and magnetic history. Analysis shows that the observed behaviors are inconsistent with the Neel-Arrhenius model of thermal activation, and are instead indicative of cooperative aging of the antiferromagnet. Our results provide new insights into the mechanisms controlling the stationary states and dynamics of ferromagnet/antiferromagnet bilayers, and potentially other frustrated magnetic systems.

  5. Antiferromagnetism in metals: from the cuprate superconductors to the heavy fermion materials.

    Science.gov (United States)

    Sachdev, Subir; Metlitski, Max A; Punk, Matthias

    2012-07-25

    The critical theory of the onset of antiferromagnetism in metals, with concomitant Fermi surface reconstruction, has recently been shown to be strongly coupled in two spatial dimensions. The onset of unconventional superconductivity near this critical point is reviewed: it involves a subtle interplay between the breakdown of fermionic quasiparticle excitations on the Fermi surface and the strong pairing glue provided by the antiferromagnetic fluctuations. The net result is a logarithm-squared enhancement of the pairing vertex for generic Fermi surfaces, with a universal dimensionless coefficient independent of the strength of interactions, which is expected to lead to superconductivity at the scale of the Fermi energy. We also discuss the possibility that the antiferromagnetic critical point can be replaced by an intermediate 'fractionalized Fermi liquid' phase, in which there is Fermi surface reconstruction but no long-range antiferromagnetic order. We discuss the relevance of this phase to the underdoped cuprates and the heavy fermion materials.

  6. Exchange biasing single molecule magnets: coupling of TbPc2 to antiferromagnetic layers.

    Science.gov (United States)

    Lodi Rizzini, A; Krull, C; Balashov, T; Mugarza, A; Nistor, C; Yakhou, F; Sessi, V; Klyatskaya, S; Ruben, M; Stepanow, S; Gambardella, P

    2012-11-14

    We investigate the possibility to induce exchange bias between single molecule magnets (SMM) and metallic or oxide antiferromagnetic substrates. Element-resolved X-ray magnetic circular dichroism measurements reveal, respectively, the presence and absence of unidirectional exchange anisotropy for TbPc(2) SMM deposited on antiferromagnetic Mn and CoO layers. TbPc(2) deposited on Mn thin films present magnetic hysteresis and a negative horizontal shift of the Tb magnetization loop after field cooling, consistent with the observation of pinned spins in the Mn layer coupled parallel to the Tb magnetic moment. Conversely, molecules deposited on CoO substrates present paramagnetic magnetization loops with no indication of exchange bias. These experiments demonstrate the ability of SMM to polarize the pinned uncompensated spins of an antiferromagnet during field-cooling and realize metal-organic exchange-biased heterostructures using antiferromagnetic pinning layers.

  7. The density matrix method in photonic bandgap and antiferromagnetic materials

    Science.gov (United States)

    Barrie, Scott B.

    emission peaks doped with four-level atoms is studied. It is found that linewidth narrowing is only dependent upon time delay when the resonance energy is not near a band edge. This is a new discovery. The density matrix method is employed to find the critical magnetic field at which spin flopping occurs in antiferromagnetic high temperature superconductors. It is found that this magnetic field depends upon the temperature, the anisotropy parameter and the doping concentration. Results are calculated for 1-2-3 HTSCs. Keywords. Quantum Optics, Density Matrix, Photonic Bandgap Materials, Dispersive Polaritonic Bandgap Materials, Antiferromagnets.

  8. Magnetoelectric and antiferromagnetic photogalvanic effects in RMn2O5 oxides: A symmetric approach

    Science.gov (United States)

    Men'shenin, V. V.

    2012-10-01

    Possible magnetic states of the commensurate antiferromagnetic manganate phase with a nonzero wave vector of the structure have been analyzed within the group-theoretical approach using only the space symmetry group. A phenomenological description of the magnetoelectric effect has been performed and the possibility of the existence of the antiferromagnetic photogalvanic effect in this phase has been established using the magnetic states obtained in this study.

  9. Finite-temperature transition of the antiferromagnetic Heisenberg model on a distorted kagome lattice.

    Science.gov (United States)

    Masuda, Hiroshi; Okubo, Tsuyoshi; Kawamura, Hikaru

    2012-08-03

    Motivated by the recent experiment on kagome-lattice antiferromagnets, we study the zero-field ordering behavior of the antiferromagnetic classical Heisenberg model on a uniaxially distorted kagome lattice by Monte Carlo simulations. A first-order transition, which has no counterpart in the corresponding undistorted model, takes place at a very low temperature. The origin of the transition is ascribed to a cooperative proliferation of topological excitations inherent to the model.

  10. Chiral Kosterlitz-Thouless transition in the frustrated Heisenberg antiferromagnet on a pyrochlore slab.

    Science.gov (United States)

    Kawamura, Hikaru; Arimori, Takuya

    2002-02-18

    Ordering of the geometrically frustrated two-dimensional Heisenberg antiferromagnet on a pyrochlore slab is studied by Monte Carlo simulations. In contrast to the kagomé Heisenberg antiferromagnet, the model exhibits locally noncoplanar spin structures at low temperatures, bearing nontrivial chiral degrees of freedom. Under certain conditions, the model exhibits a novel Kosterlitz-Thouless-type transition at a finite temperature associated with these chiral degrees of freedom.

  11. Evidence for a bicritical point in the XXZ Heisenberg antiferromagnet on a simple cubic lattice.

    Science.gov (United States)

    Selke, Walter

    2011-04-01

    The classical Heisenberg antiferromagnet with uniaxial exchange anisotropy (XXZ model) in a field on a simple cubic lattice is studied with the help of extensive Monte Carlo simulations. We analyze, in particular, various staggered susceptibilities and Binder cumulants and present clear evidence for the triple point of the antiferromagnetic, spin-flop, and paramagnetic phases being a bicritical point with Heisenberg symmetry. Results are compared to previous predictions applying various theoretical approaches.

  12. Spin Dynamics and Critical Fluctuations in a Two-Dimensional Random Antiferromagnet

    DEFF Research Database (Denmark)

    Als-Nielsen, Jens Aage; Birgeneau, R. J.; Guggenheim, H. J.

    1975-01-01

    A comprehensive elastic- and inelastic-neutron-scattering study of the binary mixed antiferromagnet Rb2Mn0.5Ni0.5F4 has been carried out. The pure materials, Rb2MnF4 and Rb2NiF4 are [2d] near-Heisenberg antiferromagnets of the K2NiF4 type. Elastic-scattering experiments demonstrate that the Mn...

  13. Structural Distortion Stabilizing the Antiferromagnetic and Semiconducting Ground State of BaMn2As2

    Directory of Open Access Journals (Sweden)

    Ekkehard Krüger

    2016-09-01

    Full Text Available We report evidence that the experimentally found antiferromagnetic structure as well as the semiconducting ground state of BaMn 2 As 2 are caused by optimally-localized Wannier states of special symmetry existing at the Fermi level of BaMn 2 As 2 . In addition, we find that a (small tetragonal distortion of the crystal is required to stabilize the antiferromagnetic semiconducting state. To our knowledge, this distortion has not yet been established experimentally.

  14. One- and Two- Magnon Excitations in a One-Dimensional Antiferromagnet in a Magnetic Field

    DEFF Research Database (Denmark)

    Heilmann, I.U.; Kjems, Jørgen; Endoh, Y.;

    1981-01-01

    We have carried out a comprehensive experimental and theoretical study of the inelastic scattering in the one-dimensional near-Heisenberg antiferromagnet (CD3)4NMnCl3 (TMMC) at low temperatures, 0.3......We have carried out a comprehensive experimental and theoretical study of the inelastic scattering in the one-dimensional near-Heisenberg antiferromagnet (CD3)4NMnCl3 (TMMC) at low temperatures, 0.3...

  15. Antiferromagnetic textures and dynamics on the surface of a heavy metal

    OpenAIRE

    Zarzuela, Ricardo; Tserkovnyak, Yaroslav

    2017-01-01

    We investigate the formation and dynamics of spin textures in antiferromagnetic insulators adjacent to a heavy-metal substrate with strong spin-orbit interactions. Exchange coupling to conduction electrons engenders an effective anisotropy, Dzyaloshinskii-Moriya interactions, and a magnetoelectric effect for the N\\'{e}el order, which can conspire to produce nontrivial antiferromagnetic textures. Current-driven spin transfer enabled by the heavy metal, furthermore, triggers ultrafast (THz) osc...

  16. Relaxation of antiferromagnetic order in spin-1/2 chains following a quantum quench.

    Science.gov (United States)

    Barmettler, Peter; Punk, Matthias; Gritsev, Vladimir; Demler, Eugene; Altman, Ehud

    2009-04-03

    We study the unitary time evolution of antiferromagnetic order in anisotropic Heisenberg chains that are initially prepared in a pure quantum state far from equilibrium. Our analysis indicates that the antiferromagnetic order imprinted in the initial state vanishes exponentially. Depending on the anisotropy parameter, oscillatory or nonoscillatory relaxation dynamics is observed. Furthermore, the corresponding relaxation time exhibits a minimum at the critical point, in contrast to the usual notion of critical slowing down, from which a maximum is expected.

  17. Antiferromagnetic resonance modes for the S = 1/2 kagome antiferromagnet Cs{sub 2}Cu{sub 3}SnF{sub 12}

    Energy Technology Data Exchange (ETDEWEB)

    Sharmin, S; Umegaki, I; Tanaka, H; Ono, T [Department of Physics, Tokyo Institute of Technology, Ookayama 2-12-1, Meguro, Tokyo 152-8551 (Japan); Tanaka, G; Nojiri, H [Institute for Materials Research, Tohoku University, Sendai 980-8577 (Japan); Fujisawa, M [Development of Frontier Research and Technology, Meguro-ku, Tokyo 152-8551 (Japan); Matsumi, N; Tomoo, M [Graduate School of Science, Kobe University, Kobe 657-8501 (Japan); Okubo, S; Ohta, H [Molecular Photoscience Research Center, Kobe University, Kobe 657-8501 (Japan); Sakurai, T, E-mail: sharmin@lee.phys.titech.ac.jp [Center for Supports to Research and Education Activities, Kobe University, Kobe 657-8501 (Japan)

    2011-07-20

    We have investigated the antiferromagnetic resonance modes of the kagome antiferromagnet Cs{sub 2}Cu{sub 3}SnF{sub 12} both theoretically and experimentally. High-field electron spin resonance experiments on single crystals were conducted in the ordered phase at different frequencies and temperatures with the external magnetic field parallel to the c axis. Considering three sublattices, we calculated the resonance modes for the motions of the sublattice magnetizations within the framework of the mean field approximation. It was found that the frequency-field diagram is in good agreement with the experimental results.

  18. Generalized hard-core dimer model approach to low-energy Heisenberg frustrated antiferromagnets: General properties and application to the kagome antiferromagnet

    Science.gov (United States)

    Schwandt, David; Mambrini, Matthieu; Poilblanc, Didier

    2010-06-01

    We propose a general nonperturbative scheme that quantitatively maps the low-energy sector of spin-1/2 frustrated Heisenberg antiferromagnets to effective generalized quantum dimer models. We develop the formal lattice-independent frame and establish some important results on (i) the locality of the generated Hamiltonians, (ii) how full resummations can be performed in this renormalization scheme. The method is then applied to the much debated kagome antiferromagnet for which a fully resummed effective Hamiltonian—shown to capture the essential properties and provide deep insights on the microscopic model [D. Poilblanc, M. Mambrini, and D. Schwandt, Phys. Rev. B 81, 180402(R) (2010)]—is derived.

  19. Ferromagnetism at the interfaces of antiferromagnetic FeRh epilayers

    Science.gov (United States)

    Fan, R.; Kinane, C. J.; Charlton, T. R.; Dorner, R.; Ali, M.; de Vries, M. A.; Brydson, R. M. D.; Marrows, C. H.; Hickey, B. J.; Arena, D. A.; Tanner, B. K.; Nisbet, G.; Langridge, S.

    2010-11-01

    The nanoscale magnetic structure of FeRh epilayers has been studied by polarized neutron reflectometry. Epitaxial films with a nominal thickness of 500Å were grown on MgO (001) substrates via molecular-beam epitaxy and capped with 20Å of MgO. The FeRh films show a clear transition from the antiferromagnetic (AF) state to the ferromagnetic (FM) state with increasing temperature. Surprisingly the films possess a FM moment even at a temperature 80 K below the AF-FM transition temperature of the film. We have quantified the magnitude and spatial extent of this FM moment, which is confined to within ˜60-80Å of the FeRh near the top and bottom interfaces. These interfacial FM layers account for the unusual effects previously observed in films with thickness <100Å . Given the delicate energy balance between the AF and FM ground states we suggest a metastable FM state resides near to the interface within an AF matrix. The length scale over which the FM region resides is consistent with the strained regions of the film.

  20. Spintronic materials and devices based on antiferromagnetic metals

    Directory of Open Access Journals (Sweden)

    Y.Y. Wang

    2017-04-01

    Full Text Available In this paper, we review our recent experimental developments on antiferromagnet (AFM spintronics mainly comprising Mn-based noncollinear AFM metals. IrMn-based tunnel junctions and Hall devices have been investigated to explore the manipulation of AFM moments by magnetic fields, ferromagnetic materials and electric fields. Room-temperature tunneling anisotropic magnetoresistance based on IrMn as well as FeMn has been successfully achieved, and electrical control of the AFM exchange spring is realized by adopting ionic liquid. In addition, promising spin-orbit effects in AFM as well as spin transfer via AFM spin waves reported by different groups have also been reviewed, indicating that the AFM can serve as an efficient spin current source. To explore the crucial role of AFM acting as efficient generators, transmitters, and detectors of spin currents is an emerging topic in the field of magnetism today. AFM metals are now ready to join the rapidly developing fields of basic and applied spintronics, enriching this area of solid-state physics and microelectronics.

  1. Griffiths phase behaviour in a frustrated antiferromagnetic intermetallic compound

    Science.gov (United States)

    Ghosh, Krishanu; Mazumdar, Chandan; Ranganathan, R.; Mukherjee, S.

    2015-10-01

    The rare coexistence of a Griffiths phase (GP) and a geometrically frustrated antiferromagnetism in the non-stoichiometric intermetallic compound GdFe0.17Sn2 (the paramagnetic Weiss temperature θp ~ -59 K) is reported in this work. The compound forms in the Cmcm space group with large structural anisotropy (b/c ~ 4). Interestingly, all the atoms in the unit cell possess the same point group symmetry (Wycoff position 4c), which is rather rare. The frustration parameter, f = |θp|/TN has been established as 3.6, with the Néel temperature TN and Griffiths temperature TG being 16.5 and 32 K, respectively. The TG has been determined from the heat capacity measurement and also from the magnetocaloric effect (MCE). It is also shown that substantial difference in GP region may exist between zero field and field cooled measurements - a fact hitherto not emphasized so far.

  2. Order by virtual crystal field fluctuations in pyrochlore XY antiferromagnets

    Science.gov (United States)

    Rau, Jeffrey G.; Petit, Sylvain; Gingras, Michel J. P.

    2016-05-01

    Conclusive evidence of order by disorder is scarce in real materials. Perhaps one of the strongest cases presented has been for the pyrochlore XY antiferromagnet Er2Ti2O7 , with the ground state selection proceeding by order by disorder induced through the effects of quantum fluctuations. This identification assumes the smallness of the effect of virtual crystal field fluctuations that could provide an alternative route to picking the ground state. Here we show that this order by virtual crystal field fluctuations is not only significant, but competitive with the effects of quantum fluctuations. Further, we argue that higher-multipolar interactions that are generically present in rare-earth magnets can dramatically enhance this effect. From a simplified bilinear-biquadratic model of these multipolar interactions, we show how the virtual crystal field fluctuations manifest in Er2Ti2O7 using a combination of strong-coupling perturbation theory and the random-phase approximation. We find that the experimentally observed ψ2 state is indeed selected and the experimentally measured excitation gap can be reproduced when the bilinear and biquadratic couplings are comparable while maintaining agreement with the entire experimental spin-wave excitation spectrum. Finally, we comment on possible tests of this scenario and discuss implications for other order-by-disorder candidates in rare-earth magnets.

  3. On Scaling Relations of Organic Antiferromagnets with Magnetic Anions

    Science.gov (United States)

    Shimahara, Hiroshi; Kono, Yuki

    2017-04-01

    We study a recently reported scaling relation of the specific heat of the organic compounds λ-(BETS)2FexGa1-xCl4. This relation suggests that the sublattice magnetization m of the π electrons and the antiferromagnetic transition temperature TN are proportional to x. Note that the scaling relation for TN can be explained by considering the effective interaction between the π electrons via the localized 3d spins on the FeCl4 anions. The effective interaction is analogous to the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction, but the roles of the conductive electrons and the localized spins are interchanged. Using available energy scales, it is shown that the TN scaling relation indicates that the system is in the vicinity of the quantum critical point. It is argued that the scaling relation for m at low temperatures, i.e., below TN but excluding temperatures in the vicinity of TN, indicates that the mismatch between the Fermi surface and that shifted by the nesting vector is large, at least for a large part of the Fermi surface. We also discuss the scaling relation near TN.

  4. Insight into the antiferromagnetic structure manipulated by electronic reconstruction

    Science.gov (United States)

    Cui, B.; Li, F.; Song, C.; Peng, J. J.; Saleem, M. S.; Gu, Y. D.; Li, S. N.; Wang, K. L.; Pan, F.

    2016-10-01

    Antiferromagnetic (AFM) materials, with robust rigidity to magnetic field perturbations and ultrafast spin dynamics, show great advantages in information storage and have developed into a fast-emerging field of AFM spintronics. However, a direct characterization of spin alignments in AFM films has been challenging, and their manipulation by lattice distortion and magnetic proximity is inevitably accompanied by "ferromagnetic" features within the AFM matrix. Here we resolve the G -type AFM structure of SrCo O2.5 and find that the interfacial AFM structure could be modulated intrinsically from in plane to out of plane with a canted angle of 60∘ by the charge transfer and orbital reconstruction in SrCo O2.5/L a2 /3S r1 /3Mn O3 heterostructures both experimentally and theoretically. Such an interfacial AFM reconfiguration caused by electronic reconstruction does not cause the ferromagnetic feature and changes the magnetization switching process of L a2 /3S r1 /3Mn O3 from in plane to perpendicular to the plane, in turn. Our study not only reveals the coupling between charge, orbital, and AFM structure, but also provides a unique approach to manipulating AFM structure.

  5. Local control of antiferromagnetic domains in Cr2O3

    Science.gov (United States)

    Adenwalla, S.; Singh, Uday; Echtenkamp, W.; Binek, Ch.

    2015-03-01

    We have used a Cr2O3/Pd/(Co/Pd)3 exchange biased heterostructure to measure the spatial distribution of anti-ferromagnetic (AFM) domains in magnetoelectric AFM Cr2O3.TheAFMCr2O3 possesses a residual roughness insensitive surface magnetization below its Néel temperature (TN 307K) This surface magnetization couples to the ferromagnetic material (Co/Pd) and results in exchange bias. Cooling the Cr2O3 from above its Néel temperature in different magnetization states of the ferromagnet results in the formation of AFM domains in Cr2O3. The AFM domains in the Cr2O3 were mapped by a spatial map of the exchange bias of the ferromagnet for the sample cooled in various remnant conditions of Co/Pd and at different temperatures. Local control of AFM domains was achieved by first, controlling the magnetization of Co/Pd multilayers and cooling below the Neel temperature, resulting in a single AFM domain, and then, subsequently writing a reversed AFM domain using the heat from a 6 mW focused laser beam. Scanning the laser beam allows for the writing of any domain pattern with a spatial resolution of 5 μm, limited only by the focusing optics. This work is supported by NSF Grant No. 1409622 and MRSEC DMR-0820521.

  6. Spin torque antiferromagnetic nanooscillator in the presence of magnetic noise

    Directory of Open Access Journals (Sweden)

    H. Gomonay

    2012-12-01

    Full Text Available Spin-torque effects in antiferromagnetic (AFM materials are of great interest due to the possible applications as high-speed spintronic devices. In the present paper we analyze the statistical properties of the current-driven AFM nanooscillator that result from the white Gaussian noise of magnetic nature. According to the peculiarities of deterministic dynamics, we derive the Langevin and Fokker-Planck equations in the energy representation of two normal modes. We find the stationary distribution function in the subcritical and overcritical regimes and calculate the current dependence of the average energy, energy fluctuation and their ratio (quality factor. The noncritical mode shows the Boltzmann statistics with the current-dependent effective temperature in the whole range of the current values. The effective temperature of the other, i.e., soft, mode critically depends on the current in the subcritical region. Distribution function of the soft mode follows the Gaussian law above the generation threshold. In the overcritical regime, the total average energy and the quality factor grow with the current value. This raises the AFM nanooscillators to the promising candidates for active spintronic components.

  7. Ultrafast Band Engineering and Transient Spin Currents in Antiferromagnetic Oxides.

    Science.gov (United States)

    Gu, Mingqiang; Rondinelli, James M

    2016-04-29

    We report a dynamic structure and band engineering strategy with experimental protocols to induce indirect-to-direct band gap transitions and coherently oscillating pure spin-currents in three-dimensional antiferromagnets (AFM) using selective phononic excitations. In the Mott insulator LaTiO3, we show that a photo-induced nonequilibrium phonon mode amplitude destroys the spin and orbitally degenerate ground state, reduces the band gap by 160 meV and renormalizes the carrier masses. The time scale of this process is a few hundreds of femtoseconds. Then in the hole-doped correlated metallic titanate, we show how pure spin-currents can be achieved to yield spin-polarizations exceeding those observed in classic semiconductors. Last, we demonstrate the generality of the approach by applying it to the non-orbitally degenerate AFM CaMnO3. These results advance our understanding of electron-lattice interactions in structures out-of-equilibrium and establish a rational framework for designing dynamic phases that may be exploited in ultrafast optoelectronic and optospintronic devices.

  8. Thermally stable magnetic skyrmions in multilayer synthetic antiferromagnetic racetracks

    Science.gov (United States)

    Zhang, Xichao; Ezawa, Motohiko; Zhou, Yan

    2016-08-01

    A magnetic skyrmion is a topological magnetization structure with a nanometric size and a well-defined swirling spin distribution, which is anticipated to be an essential building block for novel skyrmion-based device applications. We study the motion of magnetic skyrmions in multilayer synthetic antiferromagnetic (SAF) racetracks as well as in conventional monolayer ferromagnetic (FM) racetracks at finite temperature. There is an odd-even effect of the constituent FM layer number on the skyrmion Hall effect (SkHE). Namely, due to the suppression of the SkHE, the magnetic skyrmion has no transverse motion in multilayer SAF racetracks packed with even FM layers. It is shown that a moving magnetic skyrmion is stable even at room temperature (T =300 K) in a bilayer SAF racetrack but it is destructed at T =100 K in a monolayer FM racetrack. Our results indicate that the SAF structures are reliable and promising candidates for future applications in skyrmion electronics and skyrmion spintronics.

  9. High magnetic field magnetization of a new triangular lattice antiferromagnet

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, H. D. [Univ. of Tennessee, Knoxville, TN (United States); Los Alamos National Lab. (LANL), Los Alamos, NM (United States). National High Magnetic Field Lab. (MagLab); Stritzinger, Laurel Elaine Winter [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Harrison, Neil [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2017-03-23

    In CsV(MoO4)2, the magnetic V3+ ions with octahedral oxygen-coordination form a geometrically frustrated triangular lattice. So fare, there is no magnetic properties reported on it. Recently, we successfully grew single crystals of CsV(MoO4)2 by using flux method. The susceptibility shows a sharp drop around 24 K, representing a long range magnetic ordering. To understand the physical properties of this new triangular lattice antiferromagnet (TLAF), we pursued high field magnetization measurements to answer two questions: (i) what is the saturation field, which will be very useful to calculate the exchange interaction of the system? (ii) Will it exhibit spin state transition, such as the up up down phase with 1/3-saturation moment as other TLAFs? Recently, we performed VSM measurements in Cell 8, Tallahassee, NHMFL, the results show that the magnetization reaches 0.38 MuB at 34 T, which is just 19% of the full moment of 2 MuB for V3+ (3d2) ions. Apparently we need higher field to reach 1/3 value or full moment.

  10. Non-collinear antiferromagnets and the anomalous Hall effect

    Science.gov (United States)

    Kübler, J.; Felser, C.

    2014-12-01

    The anomalous Hall effect is investigated theoretically by employing density functional calculations for the non-collinear antiferromagnetic order of the hexagonal compounds Mn3Ge and Mn3Sn using various planar triangular magnetic configurations as well as unexpected non-planar configurations. The former give rise to anomalous Hall conductivities (AHC) that are found to be extremely anisotropic. For the planar cases the AHC is connected with Weyl points in the energy-band structure. If this case were observable in Mn3Ge, a large AHC of about σzx≈ 900 (Ω \\text{cm})-1 should be expected. However, in Mn3Ge it is the non-planar configuration that is energetically favored, in which case it gives rise to an AHC of σxy≈ 100 (Ω \\text{cm})-1 . The non-planar configuration allows a quantitative evaluation of the topological Hall effect that is seen to determine this value of σxy to a large extent. For Mn3Sn it is the planar configurations that are predicted to be observable. In this case the AHC can be as large as σyz≈250 (Ω \\text{cm})-1 .

  11. Spin-dynamics simulations of the triangular antiferromagnetic XY model*

    Science.gov (United States)

    Nho, Kwangsik; Landau, D. P.

    2003-03-01

    Using Monte Carlo and spin-dynamics methods, we have studied the dynamic behavior of the classical, antiferromagnetic XY model on a triangular lattice. The temporal evolutions of spin configurations were obtained by solving numerically the coupled equations of motion for each spin using fourth-order Suzuki-Trotter decompositions of exponential operators. We calculated the dynamic structure factor S(q,w) for momentum q and frequency w. Below T_KT (Kosteritz-Thouless transition), both the in-plane (S^xx) and out-of-plane (S^zz) components exhibit very strong and sharp spin-wave peaks. Well above T_KT, S^xx and S^zz apparently display a central peak, and spin-wave signatures are still seen in S^zz. In addition, we also observed an almost dispersionless domain-wall peak at high w below Tc (Ising transition), where long-range order appears in the staggered chirality[1]. We found that our results demonstrate the consistency of the dynamic finite-size scaling theory for the characteristic frequency wm and S(q,w). *Supported by NSF [1] D.H. Lee, J.D. Joannopoulos, J.W. Negele, and D.P. Landau, Phys. Rev. Lett. 52, 433 (1984)

  12. Spin-dynamics simulations of the antiferromagnetic triangular XY model*

    Science.gov (United States)

    Nho, Kwangsik; Landau, D. P.

    2002-03-01

    Using Monte Carlo and spin-dynamics methods, we have simulated the dynamic behavior of the classical, antiferromagnetic XY model on a triangular lattice. The temporal evolutions of spin configurations were obtained by solving numerically the coupled equations of motion for each spin using fourth-order Suzuki-Trotter decompositions of exponential operators. From space-and time-displaced spin-spin correlation functions and their space-time Fourier transforms we obtained the dynamic structure factor S(q,w) for momentum q and frequency w. Below T_c, where long-range order appears in the staggered chirality[1], S(q,w) exhibits very strong and sharp spin-wave peaks in the in-plane-component S^xx. We also observe two-spin-wave peaks at low w and an almost dispersionless domain-wall peak at high w. Above T_c, a weak spin-wave peak persists but the domain-wall peak disappears for all q. We have calculated the dispersion relation and the linewidth of the spin-wave peak in S^xx by fitting the line shape to simple Lorentzians. *Supported by NSF [1] D.H. Lee, J.D. Joannopoulos, J.W. Negele, and D.P. Landau, Phys. Rev. Lett. 52, 433 (1984)

  13. Phase diagram of the triangular-lattice Potts antiferromagnet

    Science.gov (United States)

    Lykke Jacobsen, Jesper; Salas, Jesús; Scullard, Christian R.

    2017-08-01

    We study the phase diagram of the triangular-lattice Q-state Potts model in the real (Q, v) -plane, where v=e^J-1 is the temperature variable. Our first goal is to provide an obviously missing feature of this diagram: the position of the antiferromagnetic critical curve. This curve turns out to possess a bifurcation point with two branches emerging from it, entailing important consequences for the global phase diagram. We have obtained accurate numerical estimates for the position of this curve by combining the transfer-matrix approach for strip graphs with toroidal boundary conditions and the recent method of critical polynomials. The second goal of this work is to study the corresponding Ap-1 RSOS model on the torus, for integer p=4, 5, \\ldots, 8 . We clarify its relation to the corresponding Potts model, in particular concerning the role of boundary conditions. For certain values of p, we identify several new critical points and regimes for the RSOS model and we initiate the study of the flows between the corresponding field theories.

  14. Three-dimensional antiferromagnetic CP(N-1) models.

    Science.gov (United States)

    Delfino, Francesco; Pelissetto, Andrea; Vicari, Ettore

    2015-05-01

    We investigate the critical behavior of three-dimensional antiferromagnetic CP(N-1) (ACP(N-1)) models in cubic lattices, which are characterized by a global U(N) symmetry and a local U(1) gauge symmetry. Assuming that critical fluctuations are associated with a staggered gauge-invariant (Hermitian traceless matrix) order parameter, we determine the corresponding Landau-Ginzburg-Wilson (LGW) model. For N=3 this mapping allows us to conclude that the three-component ACP(2) model undergoes a continuous transition that belongs to the O(8) vector universality class, with an effective enlargement of the symmetry at the critical point. This prediction is confirmed by numerical analyses of the finite-size scaling behaviors of the ACP(2) and the O(8) vector models, which show the same universal features at their transitions. We also present a renormalization-group (RG) analysis of the LGW theories for N≥4. We compute perturbative series in two different renormalization schemes and analyze the corresponding RG flow. We do not find stable fixed points that can be associated with continuous transitions.

  15. Micromagnetic theory of antiferromagnetically coupled magnetic recording media

    Science.gov (United States)

    Schabes, Manfred

    2001-03-01

    The micromagnetic theory of antiferromagnetically coupled magnetic recording media (AFC media) is discussed for the case of AFC media consisting of two ferromagnetic layers and a polarization layer.[1-2] Attention is focused on AFC media where the top layer governs the remanent magnetization while the bottom layer acts as a slave layer. Micromagnetic simulations of recorded bit transitions demonstrate a good anticorrelation of the layer magnetizations at bit transitions for this case. Calculation of MR readback pulses shows that these AFC media have pulse widths of a thin single layer magnetic recording medium with an effective MrT that is approximately given by the difference in MrT's of the top and bottom layers. Magnetic stability is set to first order by the thicker top layer and the interactions between the top and bottom layers. [1] E.E. Fullerton, D.T. Margulies, M.E. Schabes, M. Carey, B. Gurney, A. Moser, M. Best, G. Zeltzer, K. Rubin, H. Rosen, Appl. Phys. Lett. 77 (2000), 3806. [2] E.N. Abarra, A. Inomata, H. Sato, I. Okamoto, Y. Mizoshita, Appl. Phys. Lett. 77 (2000), 2581.

  16. Magnetization reversal dynamics in antiferromagnetically coupled magnetic recording media

    Science.gov (United States)

    Schabes, Manfred

    2002-03-01

    Antiferromagnetically coupled (AFC) media have been shown to provide an important extension of longitudinal magnetic data storage at high bit densities.[1,2] In this work we report the results of micromagnetic calculations to examine the magnetization reversal mechanism in two-layer AFC media as a function of bottom layer thickness and interfacial exchange coupling. It is shown that the magnetization reversal in the top and bottom layers can proceed at rather different time scales, if the interfacial energy density is small or the bottom layer thickness is large. In this case the reversal of the bottom layer may involve spin wave like oscillations that require time periods for damping that are large compared to the reversal time of the top layer. Detailed solutions of the Landau-Lifshitz-Langevin[2] equations are discussed to study these novel oscillatory excitations in AFC media at a temperature of 350 K. [1] E.E. Fullerton et al., Appl. Phys. Lett., vol.77, (2000),3806. [2] M.E. Schabes et al., IEEE Trans. Mag. MAG-37, (2001), 1432.

  17. Negative magnetoresistance in an antiferromagnetic metal β″-(EDO-TTFVODS) 2FeBr 4(DCE) 0.5

    Science.gov (United States)

    Weng, Yufeng; Yoshino, Harukazu; Fujiwara, Hideki; Sugimoto, Toyonari; Murata, Keizo

    2008-12-01

    An organic conductor β″-(EDO-TTFVODS) 2FeBr 4(DCE) 0.5, where EDO-TTFVODS is ethylenedioxytetrathiafulvalenoquinone-1,3-diselenolemethide and DCE is 1,2-dichloroethane, has been synthesized and is expected to have a strong π-d interaction. It was found that the material is metallic down to about 4 K and shows a rather slight upturn of electrical resistivity ρ below this temperature. Temperature dependence of ρ in the slight upturn region is proportional to log T and weak negative magnetoresistance (-1.7%, 2 T) at 1.4 K also appears. Besides π-d interaction screened by conducting electrons in this material, weak localization and Kondo effect are also possible to explain this negative magnetoresistance. Oscillatory behavior probably due to a quasi-two-dimensional (Q2D) Fermi surface was observed in the field-orientation dependence, and kF‖ b' was estimated to be 0.19 Å -1.

  18. Tuning magnetic properties in quasi-two-dimensional ferromagnetic Fe3‑y Ge1‑x As x Te2 (0  ⩽  x  ⩽  0.85)

    Science.gov (United States)

    Yuan, Duanduan; Jin, Shifeng; Liu, Ning; Shen, Shijie; Lin, Zhiping; Li, Kunkun; Chen, Xiaolong

    2017-03-01

    We report that Fe3GeTe2 can form a wide solid solution by substitution of As for Ge, providing an opportunity to tune the magnetic and electronic properties in this 2D material. The crystal structure, physical properties and electronic structure of iron-deficient solid solution Fe3‑y Ge1‑x As x Te2 (0  ⩽  x  ⩽  0.85) are studied. We found that the Curie temperature can substantially change from 177 K to 33 K and resistivity decreases by about 30% with the arsenic doping x from 0 to 0.85. First principles calculations demonstrate that the elongation of Fe(1)–Fe(1) dumb-bells along c axis is essentially responsible for decreasing the integrated spin density of states below Fermi level and weakening spin polarization, resulting in a decrease of Curie temperature. Our study reveals the magnetism manipulation can be realized via modification of bondlengths in 2D magnetic materials.

  19. The temperature dependences of the electron-deformation potential phonon interacting system of a quasi two dimensional system under circularly-oscillating fields in CdS, GaN and ZnO

    Energy Technology Data Exchange (ETDEWEB)

    Sug, J. Y. [Kyungpook National University, Daegu (Korea, Republic of); Lee, S. H.; Choi, S. Y. [Donga University, Busan (Korea, Republic of)

    2014-11-15

    We study the optical quantum transition line shapes and the optical quantum transition linewidths in relation to the magnetic-field-dependent properties of an electron-deformation potential phonon interaction system. We consider two systems - one is subject to right circularly oscillating external fields and the other is subject to left circularly-oscillatory external fields. We investigated theoretically the temperature dependence of the quantum optical transition of qusi-2-dimensional Landau splitting ystem in CdS, GaN and ZnO.

  20. Nematic antiferromagnetic states in bulk FeSe

    Science.gov (United States)

    Liu, Kai; Lu, Zhong-Yi; Xiang, Tao

    2016-05-01

    The existence of nematic order, which breaks the lattice rotational symmetry with nonequivalent a and b axes in iron-based superconductors, is a well-established experimental fact. An antiferromagnetic (AFM) transition is accompanying this order, observed in nearly all parent compounds, except bulk FeSe. The absence of the AFM order in FeSe casts doubt on the magnetic mechanism of iron-based superconductivity, since the nematic order is believed to be driven by the same interaction that is responsible for the superconducting pairing in these materials. Here we show, through systematic first-principles electronic structure calculations, that the ground state of FeSe is in fact strongly AFM correlated but without developing a magnetic long-range order. Actually, there are a series of staggered n -mer AFM states with corresponding energies below that of the single stripe AFM state, which is the ground state for the parent compounds of most iron-based superconductors. Here, the staggered n -mer (n any integer >1 ) means a set of n adjacent parallel spins on a line along the b axis with antiparallel spins between n -mers along both a and b axes. Moreover, different n -mers can antiparallelly mix with each other to coexist. Among all the states, we find that the lowest energy states formed by the staggered dimer, staggered trimer, and their random antiparallel aligned spin states along the b axis are quasidegenerate. The thermal average of these states does not show any magnetic long-range order, but it does possess a hidden one-dimensional AFM order along the a axis, which can be detected by elastic neutron scattering measurements. Our finding gives a natural account for the absence of long-range magnetic order and suggests that the nematicity is driven predominantly by spin fluctuations even in bulk FeSe, providing a unified description on the phase diagram of iron-based superconductors.

  1. Magnetoresistance in antiferromagnet-based spin tunnel junctions

    Science.gov (United States)

    Jungwirth, Tomas

    2012-02-01

    To date spintronics research and applications of magnetically ordered systems have focused on ferromagnets (FMs). There are, however, fundamental physical limitations for FM materials which may make them impractical to realize the full potential of spintronics. Metal FMs offer high temperature operation but the large magnetic stray fields make them unfavorable for high-density integration and metals are unsuitable for transistor and information processing applications. FM semiconductors on the other hand do not allow for high-temperature operation. We present a concept in which these limitations are circumvented in spintronics based on antiferromagnets. The concept is based on relativistic magnetic and magneto-transport anisotropy effects in nanodevices whose common characteristics is that they are an even function of the microscopic magnetic moment vector, i.e., can be equally strong in AFMs as in FMs. As a demonstration we present our experimental observation of >100% tunneling anisotropic magnetoresistance in a device with an IrMn AFM tunnel electrode [1]. We will also discuss candidate materials for high-temperature AFM semiconductor spintronics [2].[4pt] [1] B. G. Park, J.Wunderlich, X.Marti, V.Holy, Y.Kurosaki, M.Yamada, H.Yamamoto, A.Nishide, J.Hayakawa, H.Takahashi, A.B.Shick, T.Jungwirth, Nature Mat. 10, 347 (2011). [0pt] [2] T.Jungwirth, V.Nov'ak, X.Marti, M.Cukr, F.M'aca, A.B. Shick, J.Masek, P.Horodysk'a, P.Nemec, V.Hol'y, et al., Phys. Rev. B 83, 035321 (2011).

  2. Antiferromagnetic proximity effect in epitaxial CoO/NiO/MgO(001) systems.

    Science.gov (United States)

    Li, Q; Liang, J H; Luo, Y M; Ding, Z; Gu, T; Hu, Z; Hua, C Y; Lin, H-J; Pi, T W; Kang, S P; Won, C; Wu, Y Z

    2016-03-02

    Magnetic proximity effect between two magnetic layers is an important focus of research for discovering new physical properties of magnetic systems. Antiferromagnets (AFMs) are fundamental systems with magnetic ordering and promising candidate materials in the emerging field of antiferromagnetic spintronics. However, the magnetic proximity effect between antiferromagnetic bilayers is rarely studied because detecting the spin orientation of AFMs is challenging. Using X-ray linear dichroism and magneto-optical Kerr effect measurements, we investigated antiferromagnetic proximity effects in epitaxial CoO/NiO/MgO(001) systems. We found the antiferromagnetic spin of the NiO underwent a spin reorientation transition from in-plane to out-of-plane with increasing NiO thickness, with the existence of vertical exchange spring spin alignment in thick NiO. More interestingly, the Néel temperature of the CoO layer was greatly enhanced by the adjacent NiO layer, with the extent of the enhancement closely dependent on the spin orientation of NiO layer. This phenomenon was attributed to different exchange coupling strengths at the AFM/AFM interface depending on the relative spin directions. Our results indicate a new route for modifying the spin configuration and ordering temperature of AFMs through the magnetic proximity effect near room temperature, which should further benefit the design of AFM spintronic devices.

  3. Antiferromagnetic order and spin glass behavior in Dy{sub 2}CuIn{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Siouris, I.M., E-mail: jsiou@pme.duth.gr [Democritus University of Thrace (DUTH), Production and Management Engineering Department, Materials Laboratory, 67100 Xanthi (Greece); Kremer, R.K. [Max-Planck-Institut fuer Festkoerperforschung, Heisenbergstrasse 1, D-70569 Stuttgart (Germany); Hoelzel, M. [Technische Universitaet Muenchen, Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II), 85748 Garching (Germany)

    2011-11-15

    The magnetic properties of the intermetallic compound Dy{sub 2}CuIn{sub 3} have been investigated. Ac and dc-susceptibility measurements indicate an onset of antiferromagnetic ordering at T{sub N}=19.5 K and an additional frequency dependent transition at T{sub ds}{approx}9 K. Neutron diffraction studies confirm the ordered transition at 19.5{+-}1 K. The magnetic unit cell can be described by the propagation vector k=(0.25,0.25,0) with the magnetic moment {mu}=2.63(4){mu}{sub B}/Dy{sup 3+} parallel to the c-axis. Nevertheless, neutron diffraction reveals no additional magnetic phase transition around or below 9 K, which suggests that, at lower temperatures, a spin glass state may be formed in coexistence with the antiferromagnetic mode as a result of frustration and the antagonism between ferromagnetic and antiferromagnetic exchange interactions. - Highlights: > Dy{sub 2}CuIn{sub 3} is characterized by the dominance of antiferromagnetic (AF) interactions. > Geometric frustration and crystal field effects prevent the formation of the full magnetic moment on the Dy ions. > Two magnetic regimes are recognized: an AF state and a mixed AF-glassy state. > The antiferromagnetic structure of the compound has been determined.

  4. Giant Anomalous Hall Effect in the Chiral Antiferromagnet Mn3Ge

    Science.gov (United States)

    Kiyohara, Naoki; Tomita, Takahiro; Nakatsuji, Satoru

    2016-06-01

    The external field control of antiferromagnetism is a significant subject both for basic science and technological applications. As a useful macroscopic response to detect magnetic states, the anomalous Hall effect (AHE) is known for ferromagnets, but it has never been observed in antiferromagnets until the recent discovery in Mn3Sn . Here we report another example of the AHE in a related antiferromagnet, namely, in the hexagonal chiral antiferromagnet Mn3Ge . Our single-crystal study reveals that Mn3Ge exhibits a giant anomalous Hall conductivity |σx z|˜60 Ω-1 cm-1 at room temperature and approximately 380 Ω-1 cm-1 at 5 K in zero field, reaching nearly half of the value expected for the quantum Hall effect per atomic layer with Chern number of unity. Our detailed analyses on the anisotropic Hall conductivity indicate that in comparison with the in-plane-field components |σx z| and |σz y|, which are very large and nearly comparable in size, we find |σy x| obtained in the field along the c axis to be much smaller. The anomalous Hall effect shows a sign reversal with the rotation of a small magnetic field less than 0.1 T. The soft response of the AHE to magnetic field should be useful for applications, for example, to develop switching and memory devices based on antiferromagnets.

  5. Velocity of excitations in ordered, disordered, and critical antiferromagnets

    Science.gov (United States)

    Sen, Arnab; Suwa, Hidemaro; Sandvik, Anders W.

    2015-11-01

    We test three different approaches, based on quantum Monte Carlo simulations, for computing the velocity c of triplet excitations in antiferromagnets. We consider the standard S =1 /2 one- and two-dimensional Heisenberg models, as well as a bilayer Heisenberg model at its critical point. Computing correlation functions in imaginary time and using their long-time behavior, we extract the lowest excitation energy versus momentum using improved fitting procedures and a generalized moment method. The velocity is then obtained from the dispersion relation. We also exploit winding numbers to define a cubic space-time geometry, where the velocity is obtained as the ratio of the spatial and temporal lengths of the system when all winding number fluctuations are equal. The two methods give consistent results for both ordered and critical systems, but the winding number estimator is more precise. For the Heisenberg chain, we accurately reproduce the exactly known velocity. For the two-dimensional Heisenberg model, our results are consistent with other recent calculations, but with an improved statistical precision, c =1.65847 (4 ) . We also use the hydrodynamic relation c2=ρs/χ⊥(q →0 ) between c , the spin stiffness ρs, and the transversal susceptibility χ⊥, using the smallest non-zero momentum q =2 π /L . This method also is well controlled in two dimensions, but the cubic criterion for winding numbers delivers better numerical precision. In one dimension, the hydrodynamic relation is affected by logarithmic corrections which make accurate extrapolations difficult. As an application of the winding number method, for the quantum-critical bilayer model our high-precision determination of the velocity enables us to quantitatively test, at an unprecedented level, the field-theoretic low-temperature scaling forms χ =(a /c2)T and C =(b /c2) T2 . We find agreement to within 3 % with the leading 1 /N results for the factors a and b in the O (N ) model, but the agreement

  6. Temperature Dependence of Exchange Bias and Coercivity in Ferromagnetic Layer Coupled with Polycrystalline Antiferromagnetic Layer

    Institute of Scientific and Technical Information of China (English)

    ZHAO Jin-Wei; HU Jing-Guo; CHEN Guang

    2004-01-01

    The temperature dependence of exchange bias and coercivity in a ferromagnetic layer coupled with an antiferromagnetic layer is discussed.In this model,the temperature dependence comes from the thermal instability of the system states and the temperature modulated relative magnetic parameters.Morever,the thermal fluctuation of orientations of easy axes of antiferromagnetic grains at preparing has been considered.From the present model,the experimental results can be illustrated qualitatively for available magnetic parameters.Based on our discussion,we can conclude that soft ferromagnetic layer coupled by hard antiferromagnetic layer may be very applicable to design magnetic devices.In special exchange coupling,we can get high exchange bias and low coercivity almost independent of temperature for proper temperature ranges.

  7. Blume-Emery-Griffiths model on three-dimensional lattices: Consequences for the antiferromagnetic Potts model

    Science.gov (United States)

    Lapinskas, Saulius; Rosengren, Anders

    1994-06-01

    Using the cluster-variation method we study the phase diagram of the Blume-Emergy-Griffiths (BEG) model on simple cubic and face-centered cubic lattices. For the simple cubic lattice the main attention is paid to reentrant phenomena and ferrimagnetic phases occurring in a certain range of coupling constants. The results are in close agreement with Monte-Carlo data, available for parts of the phase diagram. Several ferrimagnetic phases are obtained in the vicinity of the line in parameter space, at which the model reduces to the antiferromagnetic three-state Potts model. Our results imply the existence of three phase transitions in the antiferromagnetic Potts model on the simple-cubic lattice. The phase diagrams for the BEG model on the face-centered cubic lattice are obtained in the region of antiquadrupolar ordering. Also the several ordered phases of the antiferromagnetic Potts model on this lattice are discussed.

  8. Electrical manipulation of ferromagnetic NiFe by antiferromagnetic IrMn

    Science.gov (United States)

    Tshitoyan, V.; Ciccarelli, C.; Mihai, A. P.; Ali, M.; Irvine, A. C.; Moore, T. A.; Jungwirth, T.; Ferguson, A. J.

    2015-12-01

    We demonstrate that an antiferromagnet can be employed for a highly efficient electrical manipulation of a ferromagnet. In our study, we use an electrical detection technique of the ferromagnetic resonance driven by an in-plane ac current in a NiFe/IrMn bilayer. At room temperature, we observe antidampinglike spin torque acting on the NiFe ferromagnet, generated by an in-plane current driven through the IrMn antiferromagnet. A large enhancement of the torque, characterized by an effective spin-Hall angle exceeding most heavy transition metals, correlates with the presence of the exchange-bias field at the NiFe/IrMn interface. It highlights that, in addition to the strong spin-orbit coupling, the antiferromagnetic order in IrMn governs the observed phenomenon.

  9. Electric Field Control of the Resistance of Multiferroic Tunnel Junctions with Magnetoelectric Antiferromagnetic Barriers

    Science.gov (United States)

    Merodio, P.; Kalitsov, A.; Chshiev, M.; Velev, J.

    2016-06-01

    Based on model calculations, we predict a magnetoelectric tunneling electroresistance effect in multiferroic tunnel junctions consisting of ferromagnetic electrodes and magnetoelectric antiferromagnetic barriers. Switching of the antiferromagnetic order parameter in the barrier in applied electric field by means of the magnetoelectric coupling leads to a substantial change of the resistance of the junction. The effect is explained in terms of the switching of the orientations of local magnetizations at the barrier interfaces affecting the spin-dependent interface transmission probabilities. Magnetoelectric multiferroic materials with finite ferroelectric polarization exhibit an enhanced resistive change due to polarization-induced spin-dependent screening. These results suggest that devices with active barriers based on single-phase magnetoelectric antiferromagnets represent an alternative nonvolatile memory concept.

  10. Scaling relations of three-dimensional random-exchange quantum antiferromagnets

    Science.gov (United States)

    Tan, Deng-Ruei; Jiang, Fu-Jiun

    2015-11-01

    The thermal and ground state properties of a class of three-dimensional (3D) random-exchange spin-1/2 antiferromagnets are studied using first principles quantum Monte Carlo method. Our motivation is to examine whether the newly discovered universal scaling properties, which connect the Néel temperature and the staggered magnetization density, for the clean 3D quantum dimerized Heisenberg models remain valid for the random-exchange models considered here. Remarkably, similar to the clean systems, our Monte Carlo results indicate that these scaling relations also emerge for the considered models with the introduced antiferromagnetic randomness. The scope of the validity of these scaling properties for the 3D quantum antiferromagnets is investigated as well.

  11. Spin Hall effects in metallic antiferromagnets – perspectives for future spin-orbitronics

    Directory of Open Access Journals (Sweden)

    Joseph Sklenar

    2016-05-01

    Full Text Available We investigate angular dependent spin-orbit torques from the spin Hall effect in a metallic antiferromagnet using the spin-torque ferromagnetic resonance technique. The large spin Hall effect exists in PtMn, a prototypical CuAu-I-type metallic antiferromagnet. By applying epitaxial growth, we previously reported an appreciable difference in spin-orbit torques for c- and a-axis orientated samples, implying anisotropic effects in magnetically ordered materials. In this work we demonstrate through bipolar-magnetic-field experiments a small but noticeable asymmetric behavior in the spin-transfer-torque that appears as a hysteresis effect. We also suggest that metallic antiferromagnets may be good candidates for the investigation of various unidirectional effects related to novel spin-orbitronics phenomena.

  12. Distinct spin liquids and their transitions in spin-1/2 XXZ kagome antiferromagnets.

    Science.gov (United States)

    He, Yin-Chen; Chen, Yan

    2015-01-23

    By using the density matrix renormalization group approach, we study spin-liquid phases of spin-1/2 XXZ kagome antiferromagnets. We find that the emergence of the spin-liquid phase is independent of the anisotropy of the XXZ interaction. In particular, the two extreme limits-the Ising (a strong S^{z} interaction) and the XY (zero S^{z} interaction)-host the same spin-liquid phases as the isotropic Heisenberg model. Both a time-reversal-invariant spin liquid and a chiral spin liquid with spontaneous time-reversal symmetry breaking are obtained. We show that they evolve continuously into each other by tuning the second- and the third-neighbor interactions. And last, we discuss possible implications of our results for the nature of spin liquid in nearest-neighbor XXZ kagome antiferromagnets, including the nearest-neighbor spin-1/2 kagome antiferromagnetic Heisenberg model.

  13. Spin superconductivity in the frustrated two-dimensional antiferromagnet in the square lattice

    Science.gov (United States)

    Lima, L. S.

    2017-02-01

    We use the SU(2) Schwinger boson formalism to study the spin transport in the two-dimensional S = 1 / 2 frustrated Heisenberg antiferromagnet in a square lattice, considering the second-neighbors interactions in the diagonal. We have obtained a spin superfluid behavior for the spin transport to this system similar to obtained recently to the triangular lattice. We consider an antiferromagnetic inter-chain coupling on the diagonal, J2 > 0 , and the nearest-neighbor coupling antiferromagnetic J1 > 0 . We also have in the critical temperature T0, where the correlation length ξ → 0 , that the system suffers a transition from an ordered ground state to a disordered ground state.

  14. Large magnetostriction and negative thermal expansion in the frustrated antiferromagnet ZnCr2Se4.

    Science.gov (United States)

    Hemberger, J; von Nidda, H-A Krug; Tsurkan, V; Loidl, A

    2007-04-06

    A detailed investigation of ZnCr2Se4 is presented which is dominated by strong ferromagnetic exchange but orders antiferromagnetically at TN=21 K. Specific heat and thermal expansion exhibit sharp first-order anomalies at the antiferromagnetic transition. TN is shifted to lower temperatures by external magnetic fields and finally is fully suppressed by a field of 65 kOe. The relative length change DeltaL/L(T) is unusually large and exhibits negative thermal expansion alpha below 75 K down to TN indicating strong frustration of the lattice. Magnetostriction DeltaL/L(H) reveals large values comparable to giant magnetostrictive materials. These results point to a spin-driven origin of the structural instability at TN explained in terms of competing ferromagnetic and antiferromagnetic exchange interactions.

  15. How antiferromagnetism drives the magnetization of a ferromagnetic thin film to align out of plane.

    Science.gov (United States)

    Wang, Bo-Yao; Hong, Jhen-Yong; Yang, Kui-Hon Ou; Chan, Yuet-Loy; Wei, Der-Hsin; Lin, Hong-Ji; Lin, Minn-Tsong

    2013-03-15

    Interfacial moments of an antiferromagnet are known for their prominent effects of induced coercivity enhancement and exchange bias in ferromagnetic-antiferromagnetic exchange-coupled systems. Here we report that the unpinned moments of an antiferromagnetic face-centered-cubic Mn layer can drive the magnetization of an adjacent Fe film perpendicular owing to a formation of intrinsic perpendicular anisotropy. X-ray magnetic circular dichroism and hysteresis loops show establishment of perpendicular magnetization on Fe/Mn bilayers while temperature was decreased. The fact that the magnitude of perpendicular anisotropy of the Fe layer is enhanced proportionally to the out-of-plane oriented orbital moment of the Mn unpinned layer, rather than that of Fe itself, gives evidence for the Mn unpinned moments to be the origin of the established perpendicular magnetization.

  16. Quantum oscillations in antiferromagnetic CaFe(2)As(2) on the brink of superconductivity.

    Science.gov (United States)

    Harrison, N; McDonald, R D; Mielke, C H; Bauer, E D; Ronning, F; Thompson, J D

    2009-08-12

    We report quantum oscillation measurements on CaFe(2)As(2) under strong magnetic fields-recently reported to become superconducting under pressures of as little as a kilobar. The largest observed carrier pocket occupies less than 0.05% of the paramagnetic Brillouin zone volume-consistent with Fermi surface reconstruction caused by antiferromagnetism. On comparing several alkaline earth AFe(2)As(2) antiferromagnets (with A = Ca, Sr and Ba), the dependences of the Fermi surface cross-sectional area F(α) and the effective mass m(α)(*) of the primary observed pocket on the antiferromagnetic/structural transition temperature T(s) are both found to be consistent with the case for quasiparticles in a conventional spin-density wave model. These findings suggest that the recently proposed strain-enhanced superconductivity in these materials occurs within a broadly conventional spin-density wave phase.

  17. Antiferromagnetic skyrmion crystals: Generation, topological Hall, and topological spin Hall effect

    Science.gov (United States)

    Göbel, Börge; Mook, Alexander; Henk, Jürgen; Mertig, Ingrid

    2017-08-01

    Skyrmions are topologically nontrivial, magnetic quasiparticles that are characterized by a topological charge. A regular array of skyrmions, a skyrmion crystal (SkX), features the topological Hall effect (THE) of electrons, which, in turn, gives rise to the Hall effect of the skyrmions themselves. It is commonly believed that antiferromagnetic skyrmion crystals (AFM-SkXs) lack both effects. In this Rapid Communication, we present a generally applicable method to create stable AFM-SkXs by growing a two-sublattice SkX onto a collinear antiferromagnet. As an example we show that both types of skyrmion crystals, conventional and antiferromagnetic, exist in honeycomb lattices. While AFM-SkXs with equivalent lattice sites do not show a THE, they exhibit a topological spin Hall effect. On top of this, AFM-SkXs on inequivalent sublattices exhibit a nonzero THE, which may be utilized in spintronics devices. Our theoretical findings call for experimental realization.

  18. Anisotropic magnetocaloric effect in antiferromagnetic systems: Application to EuTiO3

    Science.gov (United States)

    Alho, B. P.; Carvalho, A. Magnus G.; von Ranke, P. J.

    2014-09-01

    In this work, we theoretically predicted an anisotropic magnetocaloric effect of the same order of magnitude of the usual magnetocaloric effect for antiferromagnetic systems. The anisotropic magnetic properties come from the anti-parallel alignment of the magnetic sites and can be optimized depending on the magnetic field change. This result highlights the applicability of antiferromagnetic compounds as refrigerants based on the anisotropic magnetocaloric effect. For this purpose, we considered a Hamiltonian model, including the exchange and Zeeman interactions in a two sublattices framework. It is worth noting that no anisotropy is explicitly included on the Hamiltonian model, although the system presents an anisotropic behavior. The calculations were applied to the G-type antiferromagnetic compound EuTiO3.

  19. Relativistic Néel-Order Fields Induced by Electrical Current in Antiferromagnets

    KAUST Repository

    Železný, J.

    2014-10-06

    We predict that a lateral electrical current in antiferromagnets can induce nonequilibrium Néel-order fields, i.e., fields whose sign alternates between the spin sublattices, which can trigger ultrafast spin-axis reorientation. Based on microscopic transport theory calculations we identify staggered current-induced fields analogous to the intraband and to the intrinsic interband spin-orbit fields previously reported in ferromagnets with a broken inversion-symmetry crystal. To illustrate their rich physics and utility, we consider bulk Mn2Au with the two spin sublattices forming inversion partners, and a 2D square-lattice antiferromagnet with broken structural inversion symmetry modeled by a Rashba spin-orbit coupling. We propose an antiferromagnetic memory device with electrical writing and reading.

  20. Dynamic selective switching in antiferromagnetically-coupled bilayers close to the spin reorientation transition

    Energy Technology Data Exchange (ETDEWEB)

    Fernández-Pacheco, A., E-mail: af457@cam.ac.uk; Mansell, R.; Petit, D.; Lee, J. H.; Cowburn, R. P. [Cavendish Laboratory, University of Cambridge, J. J. Thomson Avenue, Cambridge CB3 0HE (United Kingdom); Ummelen, F. C.; Swagten, H. J. M. [Department of Applied Physics, Center for NanoMaterials, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven (Netherlands)

    2014-09-01

    We have designed a bilayer synthetic antiferromagnet where the order of layer reversal can be selected by varying the sweep rate of the applied magnetic field. The system is formed by two ultra-thin ferromagnetic layers with different proximities to the spin reorientation transition, coupled antiferromagnetically using Ruderman-Kittel-Kasuya-Yosida interactions. The different dynamic magnetic reversal behavior of both layers produces a crossover in their switching fields for field rates in the kOe/s range. This effect is due to the different effective anisotropy of both layers, added to an appropriate asymmetric antiferromagnetic coupling between them. Field-rate controlled selective switching of perpendicular magnetic anisotropy layers as shown here can be exploited in sensing and memory applications.

  1. Static and Dynamical Properties of Antiferromagnetic Skyrmions in the Presence of Applied Current and Temperature

    Science.gov (United States)

    Barker, Joseph; Tretiakov, Oleg A.

    2016-04-01

    Skyrmions are topologically protected entities in magnetic materials which have the potential to be used in spintronics for information storage and processing. However, Skyrmions in ferromagnets have some intrinsic difficulties which must be overcome to use them for spintronic applications, such as the inability to move straight along current. We show that Skyrmions can also be stabilized and manipulated in antiferromagnetic materials. An antiferromagnetic Skyrmion is a compound topological object with a similar but of opposite sign spin texture on each sublattice, which, e.g., results in a complete cancellation of the Magnus force. We find that the composite nature of antiferromagnetic Skyrmions gives rise to different dynamical behavior due to both an applied current and temperature effects.

  2. Indications of c-axis Charge Transport in Hole Doped Triangular Antiferromagnets

    Institute of Scientific and Technical Information of China (English)

    LIANG Ying; LIU Bin; FENG Shi-Ping

    2004-01-01

    The c-axis charge transport of the hole doped triangular antiferromagnet is investigated within the tJ model by considering the incoherent interlayer hopping.It is shown that the c-axis charge transport of the hole doped triangular antiferromagnet is essentially determined by the scattering from the in-plane fluctuation.The c-axis conductivity spectrum shows a lov-energy peak and the unusual high-energy broad band,while the c-axis resistivity is characterized by a crossover from the high temperature metallic-like behavior to the Iow temperature insulating-like behavior,which is qualitatively consistent with those of the hole doped square lattice antiferromagnet.

  3. Exchange bias up to room temperature in antiferromagnetic hexagonal Mn3Ge

    Science.gov (United States)

    Qian, J. F.; Nayak, A. K.; Kreiner, G.; Schnelle, W.; Felser, C.

    2014-07-01

    Mn3.04Ge0.96 has a hexagonal crystal structure, which can be stabilized by high-temperature annealing, and shows antiferromagnetic order with a small ferromagnetic component of less than 0.1μB and a coercivity of 0.45 T. In the ordered phase, magnetization curves M(H) exhibit an exchange bias of 62 mT at T = 2 K after field cooling, which is observable up to room temperature. The exchange anisotropy is suggested to originate from the exchange interaction between the host of triangular-antiferromagnetic Mn3Ge units and embedded ferrimagnetic-like clusters. Such clusters develop when excess Mn atoms occupy empty Ge sites in the original triangular-antiferromagnetic structure of Mn3Ge.

  4. Paramagnetic molecule induced strong antiferromagnetic exchange coupling on a magnetic tunnel junction based molecular spintronics device.

    Science.gov (United States)

    Tyagi, Pawan; Baker, Collin; D'Angelo, Christopher

    2015-07-31

    This paper reports our Monte Carlo (MC) studies aiming to explain the experimentally observed paramagnetic molecule induced antiferromagnetic coupling between ferromagnetic (FM) electrodes. Recently developed magnetic tunnel junction based molecular spintronics devices (MTJMSDs) were prepared by chemically bonding the paramagnetic molecules between the FM electrodes along the tunnel junction's perimeter. These MTJMSDs exhibited molecule-induced strong antiferromagnetic coupling. We simulated the 3D atomic model analogous to the MTJMSD and studied the effect of molecule's magnetic couplings with the two FM electrodes. Simulations show that when a molecule established ferromagnetic coupling with one electrode and antiferromagnetic coupling with the other electrode, then theoretical results effectively explained the experimental findings. Our studies suggest that in order to align MTJMSDs' electrodes antiparallel to each other, the exchange coupling strength between a molecule and FM electrodes should be ∼50% of the interatomic exchange coupling for the FM electrodes.

  5. Magnetic Properties of a Rare-Earth Antiferromagnetic Nanoparticle Investigated with a Quantum Simulation Model

    Institute of Scientific and Technical Information of China (English)

    LIU Zhao-Sen; Sechovsk(y) Vladimir; Divi(s) Martin

    2011-01-01

    @@ A Usov-type quantum model based on a mean-field approximation is utilized to simulate the magnetic structure of an assumed rare-earth nanoparticle consisting of an antiferromagnetic core and a paramagnetic outer shell.We study the magnetic properties in the presence and absence of an external magnetic field.Our simulation results show that the magnetic moments in the core region orientate antiferromagnetically in zero external magnetic field; an applied magnetic field rotates all of the magnetic moments in the paramagnetic shell completely to the field direction, and turns those in the core (which tries to maintain its original antiferromagnetic structure) towards the orientation in some degree; and the paramagnetic shell does not have a strong influence on the magnetic configuration of the core.%A Usov-type quantum model based on a mean-field approximation is utilized to simulate the magnetic structure of an assumed rare-earth nanoparticle consisting of an antiferromagnetic core and a paramagnetic outer shell. We study the magnetic properties in the presence and absence of an external magnetic field. Our simulation results show that the magnetic moments in the core region orientate antiferromagnetically in zero external magnetic field; an applied magnetic field rotates all of the magnetic moments in the paramagnetic shell completely to the Geld direction, and turns those in the core (which tries to maintain its original antiferromagnetic structure) towards the orientation in some degree; and the paramagnetic shell does not have a strong influence on the magnetic configuration of the core.

  6. Large anomalous Hall effect in a non-collinear antiferromagnet at room temperature.

    Science.gov (United States)

    Nakatsuji, Satoru; Kiyohara, Naoki; Higo, Tomoya

    2015-11-12

    In ferromagnetic conductors, an electric current may induce a transverse voltage drop in zero applied magnetic field: this anomalous Hall effect is observed to be proportional to magnetization, and thus is not usually seen in antiferromagnets in zero field. Recent developments in theory and experiment have provided a framework for understanding the anomalous Hall effect using Berry-phase concepts, and this perspective has led to predictions that, under certain conditions, a large anomalous Hall effect may appear in spin liquids and antiferromagnets without net spin magnetization. Although such a spontaneous Hall effect has now been observed in a spin liquid state, a zero-field anomalous Hall effect has hitherto not been reported for antiferromagnets. Here we report empirical evidence for a large anomalous Hall effect in an antiferromagnet that has vanishingly small magnetization. In particular, we find that Mn3Sn, an antiferromagnet that has a non-collinear 120-degree spin order, exhibits a large anomalous Hall conductivity of around 20 per ohm per centimetre at room temperature and more than 100 per ohm per centimetre at low temperatures, reaching the same order of magnitude as in ferromagnetic metals. Notably, the chiral antiferromagnetic state has a very weak and soft ferromagnetic moment of about 0.002 Bohr magnetons per Mn atom (refs 10, 12), allowing us to switch the sign of the Hall effect with a small magnetic field of around a few hundred oersted. This soft response of the large anomalous Hall effect could be useful for various applications including spintronics--for example, to develop a memory device that produces almost no perturbing stray fields.

  7. Evaluation of Watson-like Integrals for Hyper bcc Antiferromagnetic Lattice

    CERN Document Server

    Radosevic, S M; Kapor, D V; Pavkov-Hrvojevic, M V; Skrinjar, M G

    2010-01-01

    Watson-like integrals for a d-dimensional bcc antiferromagnetic lattice I_d(\\eta) and J_d(\\eta) and another two similar integrals are evaluated in an exact way in terms of generalized hypergeometric functions. A simple formula connecting Id and Jd+1 is given along with the differential equations for I_d(\\eta) and J_d(\\eta). An application of I_d and J_d in the theory of the Heisenberg antiferromagnet is discussed, together with possible generalizations to non-integer values of d. Corresponding integrals for sc lattices are also briefly reviewed.

  8. Neutron scattering studies of a frustrated spinel antiferromagnet in zero and high magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Matsuda, M [Quantum Beam Science Directorate, Japan Atomic Energy Agency (JAEA), Tokai, Ibaraki 319-1195 (Japan)

    2006-11-15

    A review is given of the neutron scattering studies on a frustrated spinel antiferromagnet CdCr{sub 2}O{sub 4}. As observed in ZnCr{sub 2}O{sub 4}, which has been most extensively studied in the Cr-based spinel oxides, CdCr{sub 2}O{sub 4} also shows an antiferromagnetic phase transition and a structural phase transition simultaneously, indicating a strong spin-lattice coupling. The magnetic structure of CdCr{sub 2}O{sub 4}was determined by neutron scattering studies. The neutron scattering study in magnetic field up to 10 T indicates an orientation of magnetic domains.

  9. Effective Hamiltonian and low-lying eigenenergy clustering patterns of four-sublattice antiferromagnets

    DEFF Research Database (Denmark)

    Zhang, N.G.; Henley, C.L.; Rischel, C.;

    2002-01-01

    We study the low-lying eigenenergy clustering patterns of quantum antiferromagnets with p sublattices (in particular p = 4). We treat each sublattice as a large spin, and using second-order degenerate perturbation theory, we derive the effective (biquadratic) Hamiltonian coupling the p large spins....... In order to compare with exact diagonalizations, the Hamiltonian is explicitly written for a finite-size lattice, and it contains information on energies of excited states as well as the ground state. The result is applied to the face-centered-cubic Type-I antiferromagnet of spin 1/2, including second...

  10. Bond-Dilution Effects on Two-Dimensional Spin-Gapped Heisenberg Antiferromagnets

    OpenAIRE

    Yasuda, Chitoshi; Todo, Synge; Matsumoto, Munehisa; Takayama, Hajime

    2001-01-01

    Bond-dilution effects on spin-1/2 spin-gapped Heisenberg antiferromagnets of coupled alternating chains on a square lattice are investigated by means of the quantum Monte Carlo method. It is found that, in contrast with the site-diluted system having an infinitesimal critical concentration, the bond-diluted system has a finite critical concentration of diluted bonds, $x_{c}$, above which the system is in an antiferromagnetic (AF) long-range ordered phase. In the disordered phase below $x_{c}$...

  11. Strain-Induced Ferromagnetism in Antiferromagnetic LuMnO3 Thin Films

    Science.gov (United States)

    White, J. S.; Bator, M.; Hu, Y.; Luetkens, H.; Stahn, J.; Capelli, S.; Das, S.; Döbeli, M.; Lippert, Th.; Malik, V. K.; Martynczuk, J.; Wokaun, A.; Kenzelmann, M.; Niedermayer, Ch.; Schneider, C. W.

    2013-07-01

    Single phase and strained LuMnO3 thin films are discovered to display coexisting ferromagnetic and antiferromagnetic orders. A large moment ferromagnetism (≈1μB), which is absent in bulk samples, is shown to display a magnetic moment distribution that is peaked at the highly strained substrate-film interface. We further show that the strain-induced ferromagnetism and the antiferromagnetic order are coupled via an exchange field, therefore demonstrating strained rare-earth manganite thin films as promising candidate systems for new multifunctional devices.

  12. Critical Behaviour of Pure and Site-Random Two Dimensional Antiferromagnets

    DEFF Research Database (Denmark)

    Birgenau, R. J.; Als-Nielsen, Jens Aage; Shirane, G.

    1977-01-01

    Quasielastic neutron scattering studies of the static critical behavior in the two-dimensional antiferromagnets K2NiF4, K2MnF4, and Rb2Mn0.5Ni0.5F4 are reported. For T......Quasielastic neutron scattering studies of the static critical behavior in the two-dimensional antiferromagnets K2NiF4, K2MnF4, and Rb2Mn0.5Ni0.5F4 are reported. For T...

  13. Quantum phase transition induced by Dzyaloshinskii-Moriya interactions in the kagome antiferromagnet

    OpenAIRE

    Cepas, Olivier; Fong, C. M.; Leung, P. W.; Lhuillier, C.

    2008-01-01

    We argue that the S=1/2 kagome antiferromagnet undergoes a quantum phase transition when the Dzyaloshinskii-Moriya coupling is increased. For $DD_c$ the system develops antiferromagnetic long-range order. The quantum critical point is found to be $D_c \\simeq 0.1J$ using exact diagonalizations and finite-size scaling. This suggests that the kagome compound ZnCu$_3(OH)$_6$Cl$_3$ may be in a quantum critical region controlled by this fixed point.

  14. Topological Weyl semimetals in the chiral antiferromagnetic materials Mn3Ge and Mn3Sn

    Science.gov (United States)

    Yang, Hao; Sun, Yan; Zhang, Yang; Shi, Wu-Jun; Parkin, Stuart S. P.; Yan, Binghai

    2017-01-01

    Recent experiments revealed that Mn3Sn and Mn3Ge exhibit a strong anomalous Hall effect at room temperature, provoking us to explore their electronic structures for topological properties. By ab initio band structure calculations, we have observed the existence of multiple Weyl points in the bulk and corresponding Fermi arcs on the surface, predicting antiferromagnetic Weyl semimetals in Mn3Ge and Mn3Sn. Here the chiral antiferromagnetism in the Kagome-type lattice structure is essential to determine the positions and numbers of Weyl points. Our work further reveals a new guiding principle to search for magnetic Weyl semimetals among materials that exhibit a strong anomalous Hall effect.

  15. Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet.

    Science.gov (United States)

    von Reppert, A; Pudell, J; Koc, A; Reinhardt, M; Leitenberger, W; Dumesnil, K; Zamponi, F; Bargheer, M

    2016-09-01

    We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Néel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost.

  16. Critical behavior of the three-dimensional Heisenberg antiferromagnet RbMnF3

    DEFF Research Database (Denmark)

    Coldea, R.; Cowley, R.A.; Perring, T.G.;

    1998-01-01

    The magnetic critical scattering of the near-ideal three-dimensional Heisenberg antiferromagnet (AF) RbMnF3 has been remeasured using neutron scattering. The critical dynamics has been studied in detail in the temperature range 0.77T(N) < T < 1.11T(N), where T-N is the Neel temperature. In agreem......The magnetic critical scattering of the near-ideal three-dimensional Heisenberg antiferromagnet (AF) RbMnF3 has been remeasured using neutron scattering. The critical dynamics has been studied in detail in the temperature range 0.77T(N)

  17. Disappearance of antiferromagnetic spin excitations in overdoped La2-xSrxCuO4.

    Science.gov (United States)

    Wakimoto, S; Yamada, K; Tranquada, J M; Frost, C D; Birgeneau, R J; Zhang, H

    2007-06-15

    Magnetic excitations for energies up to approximately 100 meV are studied for overdoped La(2-x)Sr(x)CuO(4) with x=0.25 and 0.30, using time-of-flight neutron spectroscopy. Comparison of spectra integrated over the width of an antiferromagnetic Brillouin zone demonstrates that the magnetic scattering at intermediate energies, 20 antiferromagnetic bubbles.

  18. Interface Coupling Transition in a Thin EpitaxialAntiferromagnetic Film Interacting with a Ferromagnetic Substrate

    Energy Technology Data Exchange (ETDEWEB)

    Finazzi, M.; Brambilla, A.; Biagioni, P.; Graf, J.; Gweon, G.-H.; Scholl, A.; Lanzara, A.; Duo, L.

    2006-09-07

    We report experimental evidence for a transition in theinterface coupling between an antiferromagnetic film and a ferromagneticsubstrate. The transition is observed in a thin epitaxial NiO film grownon top of Fe(001) as the film thickness is increased. Photoemissionelectron microscopy excited with linearly polarized x rays shows that theNiO film is antiferromagnetic at room temperature with in-plane uniaxialmagnetic anisotropy. The anisotropy axis is perpendicular to the Fesubstrate magnetization when the NiO thickness is less than about 15A,but rapidly becomes parallel to the Fe magnetization for a NiO coveragehigher than 25 A.

  19. Giant electrothermal conductivity and spin-phonon coupling in an antiferromagnetic oxide.

    Science.gov (United States)

    Chiorescu, C; Neumeier, J J; Cohn, J L

    2008-12-19

    The application of weak electric fields ( less, similar 100 V/cm) is found to dramatically enhance the lattice thermal conductivity of the antiferromagnetic insulator CaMnO3 over a broad range of temperature about the Néel ordering point (125 K). The effect is coincident with field-induced detrapping of bound electrons, suggesting that phonon scattering associated with short- and long-ranged antiferromagnetic order is suppressed in the presence of the mobilized charge. This interplay between bound charge and spin-phonon coupling might allow for the reversible control of spin fluctuations using weak external fields.

  20. Singlet Ground State Magnetism: III Magnetic Excitons in Antiferromagnetic TbP

    DEFF Research Database (Denmark)

    Knorr, K.; Loidl, A.; Kjems, Jørgen

    1981-01-01

    The dispersion of the lowest magnetic excitations of the singlet ground state system TbP has been studied in the antiferromagnetic phase by inelastic neutron scattering. The magnetic exchange interaction and the magnetic and the rhombohedral molecular fields have been determined.......The dispersion of the lowest magnetic excitations of the singlet ground state system TbP has been studied in the antiferromagnetic phase by inelastic neutron scattering. The magnetic exchange interaction and the magnetic and the rhombohedral molecular fields have been determined....

  1. Magnetic Properties of Antiferromagnetic Oxide Materials Surfaces, Interfaces, and Thin Films

    CERN Document Server

    Duò, Lamberto; Ciccacci, Franco

    2010-01-01

    This first focused treatment on a hot topic highlights fundamental aspects as well as technological applications arising from a fascinating area of condensed matter physics. The editors have excellent track records and, in light of the broadness of the topic, retain the focus on antiferromagnetic oxides. They thus cover such topics as dichroism in x-ray absorption, non-magnetic substrates, exchange bias, ferromagnetic-antiferromagnetic interface coupling and oxide multilayers, as well as imaging using soft x-ray microscopy. The result is a very timely monograph for solid state physicists and c

  2. Quantum crystal growing: adiabatic preparation of a bosonic antiferromagnet in the presence of a parabolic inhomogeneity

    DEFF Research Database (Denmark)

    Gammelmark, Søren; Eckardt, André

    2013-01-01

    We theoretically study the adiabatic preparation of an antiferromagnetic phase in a mixed Mott insulator of two bosonic atom species in a one-dimensional optical lattice. In such a system one can engineer a tunable parabolic inhomogeneity by controlling the difference of the trapping potentials...... felt by the two species. Using numerical simulations we predict that a finite parabolic potential can assist the adiabatic preparation of the antiferromagnet. The optimal strength of the parabolic inhomogeneity depends sensitively on the number imbalance between the two species. We also find...

  3. Spin-orbit torque in two-dimensional antiferromagnetic topological insulators

    KAUST Repository

    Ghosh, S.

    2017-01-24

    We investigate spin transport in two-dimensional ferromagnetic (FTI) and antiferromagnetic (AFTI) topological insulators. In the presence of an in-plane magnetization AFTI supports zero energy modes, which enables topologically protected edge conduction at low energy. We address the nature of current-driven spin torque in these structures and study the impact of spin-independent disorder. Interestingly, upon strong disorder the spin torque develops an antidamping component (i.e., even upon magnetization reversal) along the edges, which could enable current-driven manipulation of the antiferromagnetic order parameter. This antidamping torque decreases when increasing the system size and when the system enters the trivial insulator regime.

  4. Persistent nonequilibrium dynamics of the thermal energies in the spin and phonon systems of an antiferromagnet

    Directory of Open Access Journals (Sweden)

    A. von Reppert

    2016-09-01

    Full Text Available We present a temperature and fluence dependent Ultrafast X-Ray Diffraction study of a laser-heated antiferromagnetic dysprosium thin film. The loss of antiferromagnetic order is evidenced by a pronounced lattice contraction. We devise a method to determine the energy flow between the phonon and spin system from calibrated Bragg peak positions in thermal equilibrium. Reestablishing the magnetic order is much slower than the cooling of the lattice, especially around the Néel temperature. Despite the pronounced magnetostriction, the transfer of energy from the spin system to the phonons in Dy is slow after the spin-order is lost.

  5. Vectorial mapping of noncollinear antiferromagnetic structure of semiconducting FeSe surface with spin-polarized scanning tunneling microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, K. F.; Yang, Fang; Song, Y. R. [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Zhang, Xiaole [Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Chen, Xianfeng [The State Key Laboratory of Advanced Optical Communication Systems and Networks, Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Liu, Canhua; Qian, Dong; Gao, C. L., E-mail: clgao@sjtu.edu.cn; Jia, Jin-Feng [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China); Luo, Weidong, E-mail: wdluo@sjtu.edu.cn [Key Laboratory of Artificial Structures and Quantum Control (Ministry of Education), Department of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240 (China); Institute of Natural Sciences, Shanghai Jiao Tong University, Shanghai 200240 (China); Collaborative Innovation Center of Advanced Microstructures, Nanjing (China)

    2016-02-08

    Antiferromagnetic semiconductors gain increasing interest due to their possible application in spintronics. Using spin polarized scanning tunneling microscopy operating in a vector field, we mapped the noncollinear antiferromagnetic spin structure of a semiconducting hexagonal FeSe surface on the atomic scale. The surface possesses an in-plane compensated Néel structure which is further confirmed by first-principles calculations.

  6. Room Temperature Antiferromagnetic Ordering of Nanocrystalline Tb1.90Ni0.10O3

    Science.gov (United States)

    Mandal, J.; Dalal, M.; Sarkar, B. J.; Chakrabarti, P. K.

    2017-02-01

    Nanocrystalline Ni-doped terbium oxide (Tb1.90Ni0.10O3) has been synthesized by the co-precipitation method followed by annealing at 700°C for 6 h in vacuum. The crystallographic phase and the substitution of Ni2+ ions in the lattice of Tb2O3 are confirmed by Rietveld analysis of the x-ray diffraction pattern using the software MAUD. High-resolution transmission electron microscopy is also carried out to study the morphology of the sample. Magnetic measurements are carried out at different temperatures from 5 K to 300 K using a superconducting quantum interference device (SQUID) magnetometer. The dependence of the magnetization of Tb1.90Ni0.10O3 as a function of temperature ( M- T) and magnetic field ( M- H) suggests the presence of both paramagnetic and antiferromagnetic phase at room temperature, but antiferromagnetic phase dominates below ˜120 K. The lack of saturation in the M- H curve and good fitting of the M- T curve by the Johnston formula also indicate the presence of both paramagnetic and antiferromagnetic phase at room temperature. Interestingly, an antiferromagnetic to ferromagnetic phase transition is observed below ˜40 K. The result also shows a high value of magnetization at 5 K.

  7. Model of hybrid interfacial domain wall in ferromagnetic/antiferromagnetic bilayers

    Science.gov (United States)

    Zhang, Wen; Zhai, Ya; Lu, Mu; You, Biao; Zhai, Hong-Ru; Caroline, G. Morgan

    2015-04-01

    A general model of a hybrid interfacial domain wall (HIDW) in ferromagnetic/antiferromagnetic exchange biased bilayers is proposed, where an interfacial domain wall is allowed to extend into either the ferromagnetic or antiferromagnetic layer or across both. The proposition is based on our theoretical investigation on thickness and field dependences of ferromagnetic domain wall (FMDW) and antiferromagnetic domain wall (AFDW), respectively. Good match of the simulation to the hysteresis loops of a series of NiFe/FeMn exchange-biased bilayers confirms the existence of the HIDW, where the AFDW part is found to preferentially occupy the entire antiferromagnetic layer while the FMDW shrinks with the increased magnetic field as expected. The observed asymmetry between the ascending and descending branches of the hysteresis loop is explained naturally as a consequence of different partition ratios between AFDW and FMDW. Project supported by the National Basic Research Program, China (Grant No. 2010CB923404), the National Natural Science Foundation for Young Scientists of China (Grant No. 61306121), and the China Postdoctoral Science Foundation (Grant No. 2013M541580).

  8. Dynamics of the 1D Heisenberg model and optical absorption of spinons in cuprate antiferromagnetic chains

    NARCIS (Netherlands)

    Lorenzana, J.; Eder, R.

    1996-01-01

    Published in: Phys. Rev. B 55 (1997) 3358-3361 Citing articles (CrossRef) citations recorded in [Science Citation Index] Abstract: We use numerical and analytical results to construct a simple ansatz for the energy dynamical correlation function of the 1D antiferromagnetic Heisenberg model. This is

  9. Numerical study of the spin-flop transition in anisotropic spin-1/2 antiferromagnets

    NARCIS (Netherlands)

    Yunoki, S

    2002-01-01

    Magnetization processes of the spin-1/2 antiferromagnetic XXZ model in two and three spatial dimensions are studied using a quantum Monte Carlo method based on stochastic series expansions. A recently developed operator-loop algorithm enables us to show clear evidence of a first-order phase transiti

  10. Extended quantum critical phase in a magnetized spin-1/2 antiferromagnetic chain

    DEFF Research Database (Denmark)

    Stone, M.B.; Reich, D.H.; Broholm, C.

    2003-01-01

    Measurements are reported of the magnetic field dependence of excitations in the quantum critical state of the spin S=1/2 linear chain Heisenberg antiferromagnet copper pyrazine dinitrate (CuPzN). The complete spectrum was measured at k(B)T/Jless than or equal to0.025 for H=0 and H=8.7 T, where...

  11. STUDIES OF FCC HEISENBERG ANTIFERROMAGNETS BY MONTE CARLO SIMULATION ON LARGE SPIN ARRAYS

    OpenAIRE

    Minor, W.; Giebultowicz, T.

    1988-01-01

    We report Monte Carlo studies of fcc Heisenberg antiferromagnets carried out on arrays with 108,000 spins. A lattice with only JNN ≠ 0 was found to exhibit a Type I AF order despite the disordered nature of its ground state. Contrary to previous reports, our data indicate in this case a first order phase transition.

  12. Room temperature spin-polarizations of Mn-based antiferromagnetic nanoelectrodes

    Energy Technology Data Exchange (ETDEWEB)

    Yamada, Toyo Kazu, E-mail: toyoyamada@faculty.chiba-u.jp [Graduate School of Advanced Integration Science, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba-shi 263-8522, Chiba (Japan); Vazquez de Parga, Amadeo L. [Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia and Dep. Fisica de la Materia Condensada, Universidad Autónoma de Madrid, Cantoblanco, 28049 Madrid (Spain)

    2014-11-03

    Antiferromagnets produce no stray field, and therefore, a tip electrode made of antiferromagnetic material has been considered to be the most suitable choice to measure such as magnetoresistance (MR) through single isolated magnetic nanoparticles, molecules, and ultrathin films. Spin polarizations (P) of antiferromagnetic 3-nm, 6-nm, and annealed 3-nm Mn films grown on W tips with a bcc(110) apex as well as bulk-NiMn tips were obtained at 300 K by measuring MR in ultrahigh vacuum by means of spin-polarized scanning tunneling microscopy using a layerwise antiferromagnetically stacking bct-Mn(001) film electrode. The Mn-coated tips with coverages of 3 and 6 nm exhibited P values of 1 ± 1% and 3 ± 2%, respectively, which tips likely contain α- or strained Mn. With a thermal assist, the crystalline quality and the magnetic stability of the film could increase. The annealed tip exhibited P = 9 ± 2%. The bulk-NiMn tips exhibit spin polarizations of 0 or 6 ± 2% probably depending on the chemical species (Mn or Ni) present at the apex of the tip. Fe-coated W tips were used to estimate the bct-Mn(001) film spin polarization.

  13. THEORY OF PHONON-ASSISTED MULTIMAGNON OPTICAL-ABSORPTION AND BIMAGNON STATES IN QUANTUM ANTIFERROMAGNETS

    NARCIS (Netherlands)

    Lorenzana, J.; Sawatzky, G.A

    1995-01-01

    We calculate the effective charge for multimagnon infrared absorption assisted by phonons in a perovskitelike antiferromagnet and we compute the spectra for two-magnon absorption using interacting spin-wave theory. The full set of equations for the interacting two-magnon problem is presented in the

  14. Barlowite: A Spin-1/2 Antiferromagnet with a Geometrically Perfect Kagome Motif.

    Science.gov (United States)

    Han, Tian-Heng; Singleton, John; Schlueter, John A

    2014-11-28

    We present thermodynamic studies of a new spin-1/2 antiferromagnet containing undistorted kagome lattices-barlowite Cu_{4}(OH)_{6}FBr. Magnetic susceptibility gives θ_{CW}=-136  K, while long-range order does not happen until T_{N}=15  K with a weak ferromagnetic moment μkagome lattice makes charge doping promising.

  15. The Berezinskii-Kosterlitz-Thouless transition and correlations in the XY kagome antiferromagnet

    CERN Document Server

    Cherepanov, V B; Podivilov, E V

    2001-01-01

    The problem of the Berezinskii-Kosterlitz-Thouless transition in the highly frustrated XY antiferromagnetic is solved. The transition temperature is found. It is shown that the spin correlation function exponentially decays with distance even in the low-temperature phase, in contrast to the order parameter correlation function, which decays algebraically with distance

  16. Neutron-scattering cross section of the S=1/2 Heisenberg triangular antiferromagnet

    DEFF Research Database (Denmark)

    Lefmann, K.; Hedegård, P.

    1994-01-01

    In this paper we use a Schwinger-boson mean-field approach to calculate the neutron-scattering cross section from the S = 1/2 antiferromagnet with nearest-neighbor isotropic Heisenberg interaction on a two-dimensional triangular lattice. We investigate two solutions for T = 0: (i) a state with long...

  17. Superconductivity in the vicinity of antiferromagnetic order in CrAs.

    Science.gov (United States)

    Wu, Wei; Cheng, Jinguang; Matsubayashi, Kazuyuki; Kong, Panpan; Lin, Fukun; Jin, Changqing; Wang, Nanlin; Uwatoko, Yoshiya; Luo, Jianlin

    2014-11-19

    One of the common features of unconventional superconducting systems such as the heavy-fermion, high transition-temperature cuprate and iron-pnictide superconductors is that the superconductivity emerges in the vicinity of long-range antiferromagnetically ordered state. In addition to doping charge carriers, the application of external pressure is an effective and clean approach to induce unconventional superconductivity near a magnetic quantum critical point. Here we report on the discovery of superconductivity on the verge of antiferromagnetic order in CrAs via the application of external pressure. Bulk superconductivity with Tc≈2 K emerges at the critical pressure Pc≈8 kbar, where the first-order antiferromagnetic transition at T(N)≈265 K under ambient pressure is completely suppressed. The close proximity of superconductivity to an antiferromagnetic order suggests an unconventional pairing mechanism for CrAs. The present finding opens a new avenue for searching novel superconductors in the Cr and other transition metal-based systems.

  18. Model study of coexistence of Jahn-Teller distortion, antiferromagnetism and superconductivity in iron pnictide superconductors

    Science.gov (United States)

    Pradhan, B.; Goi, S. K.; Behera, Srikanta; Parida, P. K.; Mishra, R. N.

    2016-12-01

    We have proposed a theoretical model for the coexistence of superconductivity (SC), antiferromagnetism (AFM) and Jahn-Teller (JT) effect in the mean field approximation for iron based superconductors. The model is solved by using Zubarev's double-time Green's function technique to get their selfconsistent gap equations. Then these gap equations are solved numerically.

  19. Spin-orbit torques in locally and globally noncentrosymmetric crystals: Antiferromagnets and ferromagnets

    Science.gov (United States)

    Železný, J.; Gao, H.; Manchon, Aurélien; Freimuth, Frank; Mokrousov, Yuriy; Zemen, J.; Mašek, J.; Sinova, Jairo; Jungwirth, T.

    2017-01-01

    One of the main obstacles that prevents practical applications of antiferromagnets is the difficulty of manipulating the magnetic order parameter. Recently, following the theoretical prediction [J. Železný et al., Phys. Rev. Lett. 113, 157201 (2014)], 10.1103/PhysRevLett.113.157201, the electrical switching of magnetic moments in an antiferromagnet was demonstrated [P. Wadley et al., Science 351, 587 (2016)], 10.1126/science.aab1031. The switching is due to the so-called spin-orbit torque, which has been extensively studied in ferromagnets. In this phenomena a nonequilibrium spin-polarization exchange coupled to the ordered local moments is induced by current, hence exerting a torque on the order parameter. Here we give a general systematic analysis of the symmetry of the spin-orbit torque in locally and globally noncentrosymmetric crystals. We study when the symmetry allows for a nonzero torque, when is the torque effective, and its dependence on the applied current direction and orientation of magnetic moments. For comparison, we consider both antiferromagnetic and ferromagnetic orders. In two representative model crystals we perform microscopic calculations of the spin-orbit torque to illustrate its symmetry properties and to highlight conditions under which the spin-orbit torque can be efficient for manipulating antiferromagnetic moments.

  20. The magnetic properties of the spin-1 Heisenberg antiferromagnetic chain with single-ion anisotropy

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Gangsan; Zhu, Rengui, E-mail: rgzhu@mail.ahnu.edu.cn

    2015-02-15

    The magnetic properties of the spin-1 Heisenberg antiferromagnetic chain with exchange anisotropy and single-ion anisotropy are studied by the double-time Green's function method. The determinative equations for the critical temperature, the magnetization, and the zero-field susceptibility are derived analytically. The effects of the anisotropies on the magnetic properties are presented.

  1. GPU-Accelerated Population Annealing Algorithm: Frustrated Ising Antiferromagnet on the Stacked Triangular Lattice

    Science.gov (United States)

    Borovský, Michal; Weigel, Martin; Barash, Lev Yu.; Žukovič, Milan

    2016-02-01

    The population annealing algorithm is a novel approach to study systems with rough free-energy landscapes, such as spin glasses. It combines the power of simulated annealing, Boltzmann weighted differential reproduction and sequential Monte Carlo process to bring the population of replicas to the equilibrium even in the low-temperature region. Moreover, it provides a very good estimate of the free energy. The fact that population annealing algorithm is performed over a large number of replicas with many spin updates, makes it a good candidate for massive parallelism. We chose the GPU programming using a CUDA implementation to create a highly optimized simulation. It has been previously shown for the frustrated Ising antiferromagnet on the stacked triangular lattice with a ferromagnetic interlayer coupling, that standard Markov Chain Monte Carlo simulations fail to equilibrate at low temperatures due to the effect of kinetic freezing of the ferromagnetically ordered chains. We applied the population annealing to study the case with the isotropic intra- and interlayer antiferromagnetic coupling (J2/|J1| = -1). The reached ground states correspond to non-magnetic degenerate states, where chains are antiferromagnetically ordered, but there is no long-range ordering between them, which is analogical with Wannier phase of the 2D triangular Ising antiferromagnet.

  2. Studies of the magnetic structure at the ferromagnet-antiferromagnet interface.

    Science.gov (United States)

    Scholl, A; Nolting, F; Stöhr, J; Lüning, J; Seo, J W; Locquet, J P; Fompeyrine, J; Anders, S; Ohldag, H; Padmore, H A

    2001-03-01

    Antiferromagnetic layers are a scientifically challenging component in magnetoelectronic devices, such as magnetic sensors in hard-disk heads, or magnetic random-access memory (RAM) elements. In this paper, it is shown that photoelectron emission microscopy (PEEM) is capable of determining the magnetic structure at the interface of ferromagnets and antiferromagnets with high spatial resolution (down to 20 nm). Dichroism effects at the L edges of the magnetic 3d transition metals, using circularly or linearly polarized soft X-rays from a synchrotron source, give rise to a magnetic image contrast. Images, acquired with the PEEM2 experiment at the Advanced Light Source, show magnetic contrast for antiferromagnetic LaFeO3, microscopically resolving the magnetic domain structure in an antiferromagnetically ordered thin film for the first time. Magnetic coupling between LaFeO3 and an adjacent Co layer results in a complete correlation of their magnetic domain structures. From field-dependent measurements, a unidirectional anisotropy resulting in a local exchange bias of up to 30 Oe in single domains could be deduced. The elemental specificity and the quantitative magnetic sensitivity render PEEM a perfect tool to study magnetic coupling effects in multilayered thin-film samples.

  3. Antiferromagnetism and its relation to the superconducting phases of UPt3

    DEFF Research Database (Denmark)

    Isaacs, E.D.; Zschack, P.; Broholm, C.L.

    1995-01-01

    as the magnetic correlation lengths are not affected by the presence or absence of a visible splitting in the superconducting transition. The simplest models wherein antiferromagnetic order provides the symmetry-breaking field for the splitting do not provide a compete explanation of our results....

  4. Enantioselective self-assembly of antiferromagnetic hexacopper(II) wheels with chiral amino acid oxamates.

    Science.gov (United States)

    Grancha, Thais; Ferrando-Soria, Jesús; Cano, Joan; Lloret, Francesc; Julve, Miguel; De Munno, Giovanni; Armentano, Donatella; Pardo, Emilio

    2013-07-01

    The Cu(2+)-mediated self-assembly of oxamato-based ligands derived from either the (S)- or (R)-enantiomers of the amino acid valine leads to the formation of two antiferromagnetically coupled homochiral anionic hexacopper(II) wheels in the presence of templating tetramethylammonium countercations.

  5. GPU-Accelerated Population Annealing Algorithm: Frustrated Ising Antiferromagnet on the Stacked Triangular Lattice

    Directory of Open Access Journals (Sweden)

    Borovský Michal

    2016-01-01

    Full Text Available The population annealing algorithm is a novel approach to study systems with rough free-energy landscapes, such as spin glasses. It combines the power of simulated annealing, Boltzmann weighted differential reproduction and sequential Monte Carlo process to bring the population of replicas to the equilibrium even in the low-temperature region. Moreover, it provides a very good estimate of the free energy. The fact that population annealing algorithm is performed over a large number of replicas with many spin updates, makes it a good candidate for massive parallelism. We chose the GPU programming using a CUDA implementation to create a highly optimized simulation. It has been previously shown for the frustrated Ising antiferromagnet on the stacked triangular lattice with a ferromagnetic interlayer coupling, that standard Markov Chain Monte Carlo simulations fail to equilibrate at low temperatures due to the effect of kinetic freezing of the ferromagnetically ordered chains. We applied the population annealing to study the case with the isotropic intra- and interlayer antiferromagnetic coupling (J2/|J1| = −1. The reached ground states correspond to non-magnetic degenerate states, where chains are antiferromagnetically ordered, but there is no long-range ordering between them, which is analogical with Wannier phase of the 2D triangular Ising antiferromagnet.

  6. Zero-field NMR and NQR measurements of the antiferromagnet URhIn5

    Science.gov (United States)

    Sakai, H.; Kambe, S.; Tokunaga, Y.; Matsumoto, Y.; Tateiwa, N.; Haga, Y.; Fisk, Z.

    2013-07-01

    The antiferromagnet URhIn5 with the Néel temperature TN=98 K has been investigated by nuclear magnetic/quadrupole resonance (NMR/NQR). 115In-NQR spectra in the paramagnetic state give the respective electrical field gradient parameters for the locally tetragonal and orthorhombic In(1) and In(2) sites. In the antiferromagnetic state at 4.5 K, 115In-NMR spectra in the zero external field indicate a commensurate antiferromagnetic structure. The internal field at In(1) sites is found to be zero and that at In(2) sites is 21.1 kOe at 4.5 K. The temperature (T) dependence of the nuclear relaxation rates 1/T1 in the paramagnetic state shows a distinct site dependence: Korringa-type constant (T1T)-1 behavior below ˜150 K for In(1) sites and a divergent behavior of 1/T1 toward TN for In(2). The plausible antiferromagnetic structure is discussed based on these observations.

  7. Large topological Hall effect in the non-collinear phase of an antiferromagnet.

    Science.gov (United States)

    Sürgers, Christoph; Fischer, Gerda; Winkel, Patrick; Löhneysen, Hilbert V

    2014-03-05

    Non-trivial spin arrangements in magnetic materials give rise to the topological Hall effect observed in compounds with a non-centrosymmetric cubic structure hosting a skyrmion lattice, in double-exchange ferromagnets and magnetically frustrated systems. The topological Hall effect has been proposed to appear also in presence of non-coplanar spin configurations and thus might occur in an antiferromagnetic material with a highly non-collinear and non-coplanar spin structure. Particularly interesting is a material where the non-collinearity develops not immediately at the onset of antiferromagnetic order but deep in the antiferromagnetic phase. This unusual situation arises in non-cubic antiferromagnetic Mn5Si3. Here we show that a large topological Hall effect develops well below the Néel temperature as soon as the spin arrangement changes from collinear to non-collinear with decreasing temperature. We further demonstrate that the effect is not observed when the material is turned ferromagnetic by carbon doping without changing its crystal structure.

  8. Entanglement entropy and massless phase in the antiferromagnetic three-state quantum chiral clock model

    Science.gov (United States)

    Dai, Yan-Wei; Cho, Sam Young; Batchelor, Murray T.; Zhou, Huan-Qiang

    2017-01-01

    The von Neumann entanglement entropy is used to estimate the critical point hc/J ≃0.143 (3 ) of the mixed ferro-antiferromagnetic three-state quantum Potts model H =∑i[J (XiXi+1 2+Xi2Xi +1) -h Ri] , where Xi and Ri are standard three-state Potts spin operators and J >0 is the antiferromagnetic coupling parameter. This critical point value gives improved estimates for two Kosterlitz-Thouless transition points in the antiferromagnetic (β model, where Δ and β are, respectively, the chirality and coupling parameters in the clock model. These are the transition points βc≃-0.143 (3 ) at Δ =1/2 between incommensurate and commensurate phases and βc≃-7.0 (1 ) at Δ =0 between disordered and incommensurate phases. The von Neumann entropy is also used to calculate the central charge c of the underlying conformal field theory in the massless phase h ≤hc . The estimate c ≃1 in this phase is consistent with the known exact value at the particular point h /J =-1 corresponding to the purely antiferromagnetic three-state quantum Potts model. The algebraic decay of the Potts spin-spin correlation in the massless phase is used to estimate the continuously varying critical exponent η .

  9. Improved lower bounds on the ground-state entropy of the antiferromagnetic Potts model.

    Science.gov (United States)

    Chang, Shu-Chiuan; Shrock, Robert

    2015-05-01

    We present generalized methods for calculating lower bounds on the ground-state entropy per site, S(0), or equivalently, the ground-state degeneracy per site, W=e(S(0)/k(B)), of the antiferromagnetic Potts model. We use these methods to derive improved lower bounds on W for several lattices.

  10. Spin-orbit torques in locally and globally noncentrosymmetric crystals: Antiferromagnets and ferromagnets

    KAUST Repository

    Železný, J.

    2017-01-10

    One of the main obstacles that prevents practical applications of antiferromagnets is the difficulty of manipulating the magnetic order parameter. Recently, following the theoretical prediction [J. Železný, Phys. Rev. Lett. 113, 157201 (2014)]PRLTAO0031-900710.1103/PhysRevLett.113.157201, the electrical switching of magnetic moments in an antiferromagnet was demonstrated [P. Wadley, Science 351, 587 (2016)]SCIEAS0036-807510.1126/science.aab1031. The switching is due to the so-called spin-orbit torque, which has been extensively studied in ferromagnets. In this phenomena a nonequilibrium spin-polarization exchange coupled to the ordered local moments is induced by current, hence exerting a torque on the order parameter. Here we give a general systematic analysis of the symmetry of the spin-orbit torque in locally and globally noncentrosymmetric crystals. We study when the symmetry allows for a nonzero torque, when is the torque effective, and its dependence on the applied current direction and orientation of magnetic moments. For comparison, we consider both antiferromagnetic and ferromagnetic orders. In two representative model crystals we perform microscopic calculations of the spin-orbit torque to illustrate its symmetry properties and to highlight conditions under which the spin-orbit torque can be efficient for manipulating antiferromagnetic moments.

  11. Intrinsic life-time and external manipulation of Néel states in antiferromagnetic adatom spins on semiconductor surfaces

    Science.gov (United States)

    Li, Jun; Liu, Bang-Gui

    2015-06-01

    It has been proposed that antiferromagnetic Fe adatom spins on semiconductor Cu-N surfaces can be used to store information (Loth et al 2012 Science 335 196). Here, we investigate spin dynamics of such antiferromagnetic systems through Monte Carlo simulations. We find out the temperature and size laws of switching rates of Néel states and show that the Néel states can become stable enough for the information storage when the number of spins reaches one or two dozens of the Fe spins. We also explore promising methods for manipulating the Néel states. These could help realize information storage with such antiferromagnetic spin systems.

  12. Spin-flop states in a synthetic antiferromagnet and variations of unidirectional anisotropy in FeMn-based spin valves

    Science.gov (United States)

    Milyaev, M. A.; Naumova, L. I.; Chernyshova, T. A.; Proglyado, V. V.; Kulesh, N. A.; Patrakov, E. I.; Kamenskii, I. Yu.; Ustinov, V. V.

    2016-12-01

    Spin valves with a synthetic antiferromagnet have been prepared by magnetron sputtering. Regularities of the formation of single- and two-phase spin-flop states in the synthetic antiferromagnet have been studied using magnetoresistance measurements and imaging the magnetic structure. A thermomagnetic treatment of spin valve in a field that corresponds to the single-phase spin-flop state of synthetic antiferromagnet was shown to allow us to obtain a magnetically sensitive material characterized by hysteresis-free field dependence of the magnetoresistance.

  13. Antiferromagnetic order of strongly interacting fermions in a trap: real-space dynamical mean-field analysis

    Energy Technology Data Exchange (ETDEWEB)

    Snoek, M; Titvinidze, I; Toeke, C; Hofstetter, W [Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, 60438 Frankfurt/Main (Germany); Byczuk, K [Theoretical Physics III, Center for Electronic Correlations and Magnetism, Institute for Physics, University of Augsburg, 86135 Augsburg (Germany)], E-mail: snoek@itp.uni-frankfurt.de

    2008-09-15

    We apply dynamical mean-field theory to strongly interacting fermions in an inhomogeneous environment. With the help of this real-space dynamical mean-field theory (R-DMFT) we investigate antiferromagnetic states of repulsively interacting fermions with spin1/2 in a harmonic potential. Within R-DMFT, antiferromagnetic order is found to be stable in spatial regions with total particle density close to one, but persists also in parts of the system where the local density significantly deviates from half filling. In systems with spin imbalance, we find that antiferromagnetism is gradually suppressed and phase separation emerges beyond a critical value of the spin imbalance.

  14. Elastic instabilities in an antiferromagnetically ordered phase of the orbitally frustrated spinel GeCo2O4

    Science.gov (United States)

    Watanabe, Tadataka; Hara, Shigeo; Ikeda, Shin-Ichi; Tomiyasu, Keisuke

    2011-07-01

    Ultrasound velocity measurements of the orbitally frustrated spinel GeCo2O4 reveal unique elastic anomalies within the antiferromagnetic phase. Temperature dependence of shear moduli exhibits a minimum within the antiferromagnetic phase, suggesting the coupling of shear acoustic phonons to molecular spin-orbit excitations. Magnetic-field dependence of elastic moduli exhibits diplike anomalies, being interpreted as magnetic-field-induced metamagnetic and structural transitions. These elastic anomalies suggest that the survival of geometrical frustration, and the interplay of spin, orbital, and lattice degrees of freedom evoke a set of phenomena in the antiferromagnetic phase.

  15. Quantum Disordered State without Frustration in the Double Layer Heisenberg Antiferromagnet —Dimer Expansion and Projector Monte Carlo Study—

    Science.gov (United States)

    Hida, Kazuo

    1992-03-01

    The quantum disordered state (QDOS) of the spin 1/2 double layer square lattice Heisenberg antiferromagnet is studied. Using the dimer expansion from the limit of the large interlayer coupling J', the staggered susceptibility χ, the antiferromagnetic structure factor Sπ and the antiferromagnetic correlation length ξ are calculated up to the 6-th order in the intralayer coupling J. The ratio analysis shows that the QDOS becomes unstable against the Néel ordering at J'/J≃2.56. The critical exponents are not inconsistent with the universality class of the 3-dimensional classical Heisenberg model, suggesting that our QDOS corresponds to that expected in the 2-dimensional square lattice Heisenberg antiferromagnet with unphysically small spin (<0.276). The results of the projector Monte Carlo simulation also confirms the dimer expansion results.

  16. Synthesis and characterization of the new two-dimensional Heisenberg antiferromagnet double perovskite BaLaCuSbO6.

    Science.gov (United States)

    Blanco, M Cecilia; Paz, Sergio Alexis; Nassif, Vivian M; Guimpel, Julio J; Carbonio, Raúl E

    2015-06-21

    The BaLaCuSbO(6) double perovskite has been successfully synthesized by solid state reaction under an air atmosphere. Its structure was refined using powder neutron diffraction in the monoclinic space group I2/m with a 4% antisite disorder on the B cations. Magnetic measurements give signs of 2D-antiferromagnetic behaviour with TN around 64 K. The Jahn-Teller distortion produced by Cu(2+) ions favours a crystallographic tetragonal distortion and consequently the in-plane super-superexchange antiferromagnetic interactions, J(90°), are favoured over the in-plane J(180°) antiferromagnetic exchange interactions. Both, J and J' magnetic interactions have been evaluated according to a Heisenberg antiferromagnetic rectangular model using an approximation to Curie's law in powers of J/T, being |J| around 10 times stronger than |J'|.

  17. Order-disorder quantum phase transition in the quasi-one-dimensional spin-1/2 collinear antiferromagnetic Heisenberg model.

    Science.gov (United States)

    Rufo, Sabrina; Mendonça, Griffith; Plascak, J A; de Sousa, J Ricardo

    2013-09-01

    The ground-state properties of the quasi-one-dimensional spin-1/2 antiferromagnetic Heisenberg model is investigated by using a variational method. Spins on chains along the x direction are antiferromagnetically coupled with exchange J>0, while spins between chains in the y direction are coupled either ferromagnetically (J' 0). The staggered and the colinear antiferromagnetic magnetizations are computed and their dependence on the anisotropy parameter λ=|J'|/J is analyzed. It is found that an infinitesimal interchain coupling parameter is sufficient to stabilize a long-range order with either a staggered magnetization m_{s} (J' > 0) or a colinear antiferromagnetic magnetization m_{caf} (J' < 0), both behaving as ≃λ¹/² for λ → 0.

  18. Optical second harmonic generation induced by picosecond terahertz pulses in centrosymmetric antiferromagnet NiO

    Science.gov (United States)

    Ovchinnikov, A. V.; Chefonov, O. V.; Agranat, M. B.; Grishunin, K. A.; Il'in, N. A.; Pisarev, R. V.; Kimel, A. V.; Kalashnikova, A. M.

    2016-10-01

    Optical second harmonic generation at the photon energy of 2ℏω = 2eV in the model centrosymmetric antiferromagnet NiO irradiated with picosecond terahertz pulses (0.4-2.5 THz) at room temperature is detected. The analysis of experimental results shows that induced optical second harmonic generation at the moment of the impact of a terahertz pulse arises through the electric dipole mechanism of the interaction of the electric field of a pump pulse with the electron subsystem of NiO. Temporal changes in optical second harmonic generation during 7 ps after the action of the pulse are also of an electric dipole origin and are determined by the effects of propagation of the terahertz pulse in a NiO platelet. Coherent oscillations of spins at the antiferromagnetic resonance frequency induced by the magnetic component of the terahertz pulse induce a relatively weak modulation of magnetic dipole optical second harmonic generation.

  19. Many-body ab initio study of antiferromagnetic {Cr7M } molecular rings

    Science.gov (United States)

    Chiesa, A.; Carretta, S.; Santini, P.; Amoretti, G.; Pavarini, E.

    2016-12-01

    Antiferromagnetic molecular rings are widely studied both for fundamental quantum-mechanical issues and for technological applications, particularly in the field of quantum information processing. Here we present a detailed first-principles study of two families—purple and green—of {Cr7M } antiferromagnetic rings, where M is a divalent transition metal ion (M =Ni2 + , Mn2 +, and Zn2 +). We employ a recently developed flexible and efficient scheme to build ab initio system-specific Hubbard models. From such many-body models we systematically derive the low-energy effective spin Hamiltonian for the rings. Our approach allows us to calculate isotropic as well as anisotropic terms of the spin Hamiltonian, without any a priori assumption on its form. For each compound we calculate magnetic exchange couplings, zero-field splitting tensors, and gyromagnetic tensors, finding good agreement with experimental results.

  20. Magnetic structure study of antiferromagnet NpPtGa{sub 5} by neutron diffraction

    Energy Technology Data Exchange (ETDEWEB)

    Jonen, S. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195 (Japan)], E-mail: jonen.shintaro@jaea.go.jp; Metoki, N. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195 (Japan); Department of Physics, Tohoku University, Sendai 980-8578 (Japan); Yamamoto, E. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195 (Japan); Homma, Y.; Aoki, D. [Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Shiokawa, Y. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195 (Japan); Institute for Materials Research, Tohoku University, Oarai, Ibaraki 311-1313 (Japan); Onuki, Y. [Advanced Science Research Center, Japan Atomic Energy Agency, Tokai, Naka, Ibaraki 319-1195 (Japan); Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043 (Japan)

    2008-01-10

    The magnetic structure of NpPtGa{sub 5}was investigated by neutron diffraction. NpPtGa{sub 5} exhibits an A-type antiferromagnetic structure with propagation vector q{sup {yields}}=(0,0,1/2) below T{sub N}=26 K. The estimated Np magnetic moment is 0.38(5) {mu}{sub B}, and it is oriented parallel to the <100> direction. This small moment would be consistent with the large {gamma}=123 mJ/(K{sup 2} mol), indicative of the heavy fermion nature. The field-induced anomaly in the magnetic susceptibility is clarified to be a signature for an antiferromagnetic domain change between multi-domains to single-domain states.

  1. Easy moment direction and antiferromagnetic domain wall motion in Mn2Au

    Science.gov (United States)

    Barthem, Vitoria M. T. S.; Colin, Claire V.; Haettel, Richard; Dufeu, Didier; Givord, Dominique

    2016-05-01

    The interest of giving active functions to antiferromagnetic (AFM) materials in spintronics devices has been realized recently. Mn2Au is a high-Néel temperature antiferromagnet with large Mn moment, lying in plane of the tetragonal structure. To determine the direction of the moments in Mn2Au, an original approach is demonstrated, which should be generic to planar AFM materials. It involves the rotation of the granular sample around an axis perpendicular to the applied magnetic field. The family of easy moment directions is . For grains prevented from rotating, the dominant magnetization process is AFM domain wall motion. Textured Mn2Au nanoelements could be introduced in spintronics devices, in which the Mn moments would be switched under modest external excitation.

  2. Mapping motion of antiferromagnetic interfacial uncompensated magnetic moment in exchange-biased bilayers

    Science.gov (United States)

    Zhou, X.; Ma, L.; Shi, Z.; Fan, W. J.; Evans, R. F. L.; Zheng, Jian-Guo; Chantrell, R. W.; Mangin, S.; Zhang, H. W.; Zhou, S. M.

    2015-03-01

    In this work, disordered-IrMn3/insulating-Y3Fe5O12 exchange-biased bilayers are studied. The behavior of the net magnetic moment ΔmAFM in the antiferromagnet is directly probed by anomalous and planar Hall effects, and anisotropic magnetoresistance. The ΔmAFM is proved to come from the interfacial uncompensated magnetic moment. We demonstrate that the exchange bias and rotational hysteresis loss are induced by partial rotation and irreversible switching of the ΔmAFM. In the athermal training effect, the state of the ΔmAFM cannot be recovered after one cycle of hysteresis loop. This work highlights the fundamental role of the ΔmAFM in the exchange bias and facilitates the manipulation of antiferromagnetic spintronic devices.

  3. Itinerant antiferromagnetism in the Mott compound V1.973O3

    Science.gov (United States)

    Bao, Wei; Broholm, C.; Honig, J. M.; Metcalf, P.; Trevino, S. F.

    1996-08-01

    The doping-induced metallic state of the Mott system V2-yO3 has spin-density-wave order for Tantiferromagnetic Bragg point. The q, ω, and T dependence of magnetic fluctuations can be described by the self-consistent renormalization theory for weak itinerant antiferromagnets developed by Moriya, Hasegawa, and Nakayama. Thermodynamic properties below ~10TN are quantitatively accounted for by this theory in its simplest form with only four parameters, which are determined by our neutron-scattering experiment.

  4. Evidence for a gapped spin-liquid ground state in a kagome Heisenberg antiferromagnet.

    Science.gov (United States)

    Fu, Mingxuan; Imai, Takashi; Han, Tian-Heng; Lee, Young S

    2015-11-06

    The kagome Heisenberg antiferromagnet is a leading candidate in the search for a spin system with a quantum spin-liquid ground state. The nature of its ground state remains a matter of active debate. We conducted oxygen-17 single-crystal nuclear magnetic resonance (NMR) measurements of the spin-1/2 kagome lattice in herbertsmithite [ZnCu3(OH)6Cl2], which is known to exhibit a spinon continuum in the spin excitation spectrum. We demonstrated that the intrinsic local spin susceptibility χ(kagome), deduced from the oxygen-17 NMR frequency shift, asymptotes to zero below temperatures of 0.03J, where J ~ 200 kelvin is the copper-copper superexchange interaction. Combined with the magnetic field dependence of χ(kagome) that we observed at low temperatures, these results imply that the kagome Heisenberg antiferromagnet has a spin-liquid ground state with a finite gap.

  5. The anti-ferromagnetic Ising model on the simplest pure Husimi lattice: An exact solution

    Energy Technology Data Exchange (ETDEWEB)

    Jurčišinová, E., E-mail: jurcisine@saske.sk [Institute of Experimental Physics, SAS, Watsonova 47, 040 01 Košice (Slovakia); Jurčišin, M., E-mail: jurcisin@saske.sk [Institute of Experimental Physics, SAS, Watsonova 47, 040 01 Košice (Slovakia); Bobák, A., E-mail: andrej.bobak@upjs.sk [Department of Theoretical Physics and Astrophysics, Faculty of Science, P.J. Šafárik University, Park Angelinum 9, 040 01 Košice (Slovakia)

    2013-11-22

    The anti-ferromagnetic spin-1/2 Ising model on the pure Husimi lattice with three sites in the elementary polygon (p=3) and the coordination number z=4 is investigated. It represents the simplest approximation of the anti-ferromagnetic Ising model on the two-dimensional kagome lattice which takes into account effects of frustration. The exact analytical solution of the model is found and discussed. It is proven that the model does not exhibit the first order as well as the second order phase transitions. A detailed analysis of the magnetization properties is performed and the existence of the magnetization plateaus for low temperatures is shown. All possible ground states of the model are found and discussed.

  6. Surface antiferromagnetism and incipient metal-insulator transition in strained manganite films

    KAUST Repository

    Cossu, Fabrizio

    2013-06-21

    Using first-principles calculations, we show that the (001) surface of the ferromagnet La0.7Sr0.3MnO3 under an epitaxial compressive strain favors antiferromagnetic (AF) order in the surface layers, coexisting with ferromagnetic (FM) bulk order. Surface antiferromagnetism is accompanied by a very marked surface-related spectral pseudogap, signaling an incomplete metal-insulator transition at the surface. The different relaxation and rumpling of the MnO2 and LaO surface planes in the two competing magnetic phases cause distinct work-function changes, which are of potential diagnostic use. The AF phase is recognized as an extreme surface-assisted case of the combination of in-plane AF super-exchange and vertical FM double-exchange couplings that rules magnetism in manganites under in-plane compression.

  7. Magnetostriction and Magnetostructural Domains in Antiferromagnetic YBa2Cu3O6.

    Science.gov (United States)

    Náfrádi, B; Keller, T; Hardy, F; Meingast, C; Erb, A; Keimer, B

    2016-01-29

    We use high-resolution neutron Larmor diffraction and capacitative dilatometry to investigate spontaneous and forced magnetostriction in undoped, antiferromagnetic YBa_{2}Cu_{3}O_{6.0}, the parent compound of a prominent family of high-temperature superconductors. Upon cooling below the Néel temperature T_{N}=420  K, Larmor diffraction reveals the formation of magnetostructural domains of characteristic size ∼240  nm. In the antiferromagnetic state, dilatometry reveals a minute (4×10^{-6}) orthorhombic distortion of the crystal lattice in external magnetic fields. We attribute these observations to exchange striction and spin-orbit coupling induced magnetostriction, respectively, and show that they have an important influence on the thermal and charge transport properties of undoped and lightly doped cuprates.

  8. Electric Control of Dirac Quasiparticles by Spin-Orbit Torque in an Antiferromagnet

    Science.gov (United States)

    Šmejkal, L.; Železný, J.; Sinova, J.; Jungwirth, T.

    2017-03-01

    Spin orbitronics and Dirac quasiparticles are two fields of condensed matter physics initiated independently about a decade ago. Here we predict that Dirac quasiparticles can be controlled by the spin-orbit torque reorientation of the Néel vector in an antiferromagnet. Using CuMnAs as an example, we formulate symmetry criteria allowing for the coexistence of topological Dirac quasiparticles and Néel spin-orbit torques. We identify the nonsymmorphic crystal symmetry protection of Dirac band crossings whose on and off switching is mediated by the Néel vector reorientation. We predict that this concept verified by minimal model and density functional calculations in the CuMnAs semimetal antiferromagnet can lead to a topological metal-insulator transition driven by the Néel vector and to the topological anisotropic magnetoresistance.

  9. Spin-1/2 Heisenberg Antiferromagnet on the Spatially Anisotropic Kagome Lattice

    Science.gov (United States)

    Schnyder, Andreas; Starykh, Oleg; Balents, Leon

    2008-03-01

    We study the quasi-one-dimensional limit of the Spin-1/2 quantum antiferromagnet on the Kagome lattice, a model Hamiltonian that might be of relevance for the mineral volborthite [1,2]. The lattice is divided into antiferromagnetic spin-chains (exchange J) that are weakly coupled via intermediate ``dangling'' spins (exchange J'). Using bosonization, renormalization group methods, and current algebra techniques we determine the ground state as a function of J'/J. The case of a strictly one-dimensional Kagome strip is also discussed. [1] Z. Hiroi, M. Hanawa, N. Kobayashi, M. Nohara, Hidenori Takagi, Y. Kato, and M. Takigawa, J. Phys. Soc. Japan 70, 3377 (2001). [2] F. Bert, D. Bono, P. Mendels, F. Ladieu, F. Duc, J.-C. Trumbe, and P. Millet, Phys. Rev. Lett. 95, 087203 (2005).

  10. The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Wen; Zhou, Zhaofeng, E-mail: zfzhou@xtu.edu.cn; Zhong, Yuan; Zhang, Ting; Huang, Yongli [Key Laboratory of Low-Dimensional Materials and Application Technologies(Ministry of Education)Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Hunan Provincial Key Laboratory of Thin Film Materials and Devices, Faculty of Materials Science and Engineering, Xiangtan University, Hunan 411105 (China); Sun, Changqing [NOVITAS, School of Electrical and Electronic Engineering, Nanyang Technological University, Singapore 639798 (Singapore)

    2015-11-15

    Incorporating the bond order-length-strength (BOLS) notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (T{sub N}) of antiferromagnetic nanomaterials. Reproduction of the size trends reveals that surface atomic undercoordination induces bond contraction, and interfacial hetero-coordination induces bond nature alteration. Both surface and interface of nanomaterials modulate the T{sub N} by adjusting the atomic cohesive energy. The T{sub N} is related to the atomic cohesive/exchange energy that is lowered by the coordination number (CN) imperfection of the undercoordinated atoms near the surface and altered by the changed bond nature of epitaxial interface. A numerical match between predictions and measurements reveals that the T{sub N} of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number.

  11. The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

    Directory of Open Access Journals (Sweden)

    Wen Zhang

    2015-11-01

    Full Text Available Incorporating the bond order-length-strength (BOLS notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (TN of antiferromagnetic nanomaterials. Reproduction of the size trends reveals that surface atomic undercoordination induces bond contraction, and interfacial hetero-coordination induces bond nature alteration. Both surface and interface of nanomaterials modulate the TN by adjusting the atomic cohesive energy. The TN is related to the atomic cohesive/exchange energy that is lowered by the coordination number (CN imperfection of the undercoordinated atoms near the surface and altered by the changed bond nature of epitaxial interface. A numerical match between predictions and measurements reveals that the TN of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number.

  12. The effect of surface and interface on Neel transition temperature of low-dimensional antiferromagnetic materials

    Science.gov (United States)

    Zhang, Wen; Zhou, Zhaofeng; Zhong, Yuan; Zhang, Ting; Huang, Yongli; Sun, Changqing

    2015-11-01

    Incorporating the bond order-length-strength (BOLS) notion with the Ising premise, we have modeled the size dependence of the Neel transition temperature (TN) of antiferromagnetic nanomaterials. Reproduction of the size trends reveals that surface atomic undercoordination induces bond contraction, and interfacial hetero-coordination induces bond nature alteration. Both surface and interface of nanomaterials modulate the TN by adjusting the atomic cohesive energy. The TN is related to the atomic cohesive/exchange energy that is lowered by the coordination number (CN) imperfection of the undercoordinated atoms near the surface and altered by the changed bond nature of epitaxial interface. A numerical match between predictions and measurements reveals that the TN of antiferromagnetic nanomaterials declines with reduced size and increases with both the strengthening of heterogeneous bond and the increase of the bond number.

  13. Self-assembly of magnetic Ni nanoparticles into 1D arrays with antiferromagnetic order.

    Science.gov (United States)

    Bliznyuk, V; Singamaneni, S; Sahoo, S; Polisetty, S; He, Xi; Binek, Ch

    2009-03-11

    In this paper, we report on the magnetic properties of isolated nanoparticles and interacting nanochains formed by the self-assembly of Ni nanoparticles. The magnetic properties were studied using superconducting quantum interference device (SQUID) magnetometry and magnetic force microscopy (MFM). We demonstrate that single-domain Ni nanoparticles spontaneously form one-dimensional (1D) chains under the influence of an external magnetic field. Furthermore, such magnetic field-driven self-assembly in conjunction with surface templating produces regular arrays of 1D nanochains with antiferromagnetic intra-chain order. The antiferromagnetic order, which is in striking contrast to what is found for non-interacting nanoparticle assemblies within the chains, can be evidenced from MFM and SQUID measurements.

  14. Self-assembly of magnetic Ni nanoparticles into 1D arrays with antiferromagnetic order

    Science.gov (United States)

    Bliznyuk, V.; Singamaneni, S.; Sahoo, S.; Polisetty, S.; He, Xi; Binek, Ch

    2009-03-01

    In this paper, we report on the magnetic properties of isolated nanoparticles and interacting nanochains formed by the self-assembly of Ni nanoparticles. The magnetic properties were studied using superconducting quantum interference device (SQUID) magnetometry and magnetic force microscopy (MFM). We demonstrate that single-domain Ni nanoparticles spontaneously form one-dimensional (1D) chains under the influence of an external magnetic field. Furthermore, such magnetic field-driven self-assembly in conjunction with surface templating produces regular arrays of 1D nanochains with antiferromagnetic intra-chain order. The antiferromagnetic order, which is in striking contrast to what is found for non-interacting nanoparticle assemblies within the chains, can be evidenced from MFM and SQUID measurements.

  15. DMRG studies of the frustrated kagome antiferromagnets and the application to volborthite

    Science.gov (United States)

    Gong, Shou-Shu; Sheng, D. N.; Yang, Kun

    Motivated by the recent magnetization measurements on the high-quality single crystals of the kagome antiferromagnet volborthite, we study the ground state and magnetization properties of two kagome models proposed from the electronic structure simulations, which treat the volborthite as either the coupled trimers or the coupled frustrated chains on the kagome lattice. We study the models using density-matrix renormalization group on the cylinder geometry with the system width up to 4 legs. We find a quantum phase diagram of the models with changing couplings, and identify the magnetic properties of each phase. In the antiferromagnetic phases, we also study the magnetization curve and the different phases in the magnetic field. Finally, we compare the magetization properties of the models with the experimental observations of volborthite. NSF DMR-1157490, DMR-1408560, and the State of Florida.

  16. Dynamic zero modes of Dirac fermions and competing singlet phases of antiferromagnetic order

    CERN Document Server

    Goswami, Pallab

    2016-01-01

    In quantum spin systems, singlet phases often develop in the vicinity of an antiferromagnetic order. Typical settings for such problems arise when itinerant fermions are also present. In this work, we develop a theoretical framework for addressing such competing orders in an itinerant system, described by Dirac fermions strongly coupled to an O(3) nonlinear sigma model. We focus on two spatial dimensions, where upon disordering the antiferromagnetic order by quantum fluctuations the singular tunneling events also known as (anti)hedgehogs can nucleate competing singlet orders in the paramagnetic phase. In the presence of an isolated hedgehog configuration of the nonlinear sigma model field, we show that the fermion determinant vanishes as the dynamic Euclidean Dirac operator supports fermion zero modes of definite chirality. This provides a topological mechanism for suppressing the tunneling events. Using the methodology of quantum chromodynamics, we evaluate the fermion determinant in the close proximity of m...

  17. Fragile antiferromagnetism in the heavy-fermion compound YbBiPt

    Energy Technology Data Exchange (ETDEWEB)

    Ueland, Benjamin G. [Ames Laboratory; Kreyssig, Andreas [Ames Laboratory; Prokes, K. [Helmholtz-Zentrum Berlin fur Materialien und Energie; Lynn, J. W. [NIST Center for Neutron Research; Harriger, L. W. [NIST Center for Neutron Research; Pratt, D. K. [NIST Center for Neutron Research; Singh, D. K. [NIST Center for Neutron Research; Heitmann, T. W. [University of Missouri; Sauerbrei, Samantha [Ames Laboratory; Saunders, Scott M. [Ames Laboratory; Mun, E. D. [Ames Laboratory; Budko, Serguei L. [Ames Laboratory; McQueeney, Robert J. [Ames Laboratory; Canfield, Paul C. [Ames Laboratory; Goldman, Alan I. [Ames Laboratory

    2014-05-08

    We report results from neutron scattering experiments on single crystals of YbBiPt that demonstrate antiferromagnetic order characterized by a propagation vector, τAFM = (121212), and ordered moments that align along the [1 1 1] direction of the cubic unit cell. We describe the scattering in terms of a two-Gaussian peak fit, which consists of a narrower component that appears below TN≈0.4 K and corresponds to a magnetic correlation length of ξn≈ 80 Å, and a broad component that persists up to T*≈ 0.7 K and corresponds to antiferromagnetic correlations extending over ξb≈ 20 Å. Our results illustrate the fragile magnetic order present in YbBiPt and provide a path forward for microscopic investigations of the ground states and fluctuations associated with the purported quantum critical point in this heavy-fermion compound.

  18. Current driven spin–orbit torque oscillator: ferromagnetic and antiferromagnetic coupling

    Science.gov (United States)

    Johansen, Øyvind; Linder, Jacob

    2016-01-01

    We consider theoretically the impact of Rashba spin–orbit coupling on spin torque oscillators (STOs) in synthetic ferromagnets and antiferromagnets that have either a bulk multilayer or a thin film structure. The synthetic magnets consist of a fixed polarizing layer and two free magnetic layers that interact through the Ruderman-Kittel-Kasuya-Yosida interaction. We determine analytically which collinear states along the easy axis that are stable, and establish numerically the phase diagram for when the system is in the STO mode and when collinear configurations are stable, respectively. It is found that the Rashba spin–orbit coupling can induce anti-damping in the vicinity of the collinear states, which assists the spin transfer torque in generating self-sustained oscillations, and that it can substantially increase the STO part of the phase diagram. Moreover, we find that the STO phase can extend deep into the antiferromagnetic regime in the presence of spin–orbit torques. PMID:27653357

  19. Numerical simulation of optical bi-stability in antiferromagnetic sandwich structure

    Energy Technology Data Exchange (ETDEWEB)

    Sun Dongmei [Provincial Key Laboratory of Low Dimensional and Mesoscopic Physics, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025 (China); Fu Shufang, E-mail: shufangfu@yahoo.com [Provincial Key Laboratory of Low Dimensional and Mesoscopic Physics, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025 (China); Zhou Sheng; Wang Xuanzhang [Provincial Key Laboratory of Low Dimensional and Mesoscopic Physics, School of Physics and Electronic Engineering, Harbin Normal University, Harbin 150025 (China)

    2012-01-15

    The magnetically optical bi-stability, a third-order nonlinear response, is investigated on an antiferromagnetic (AF) sandwich structure, where an AF film is sandwiched between two dielectric films. The configuration with the AF anisotropy axis and external static magnetic field both in the interfaces and normal to the incident plane is used. The incident wave is taken as a TE wave with its electric component transverse to the incident plane. We find that bistable switches can appear only in a finite frequency range and an incident angle range for a given regime of incident power, which means that there are the critical incident angle and frequency. The power threshold value for the bi-stability increases with the incident angle. In addition, the bi-stability also easily is modulated by the external magnetic field. - Highlights: > Antiferromagnetic sandwich NM/AF/NM. > Optical bi-stability near the resonant frequency. > Effect of magnetic field and incident angle.

  20. Weak antiferromagnetic order and superconductivity in UPt 3 studied by neutron scattering

    Science.gov (United States)

    van Dijk, N. H.; Rodière, P.; Fåk, B.; Huxley, A.; Flouquet, J.

    2002-07-01

    The heavy-fermion superconductor UPt 3 is one of the best-studied examples of systems that show unconventional superconductivity. Below a transition temperature of Tc=0.55 K a complex phase diagram with three different superconducting phases is observed as a function of temperature, magnetic field, and pressure. The weak antiferromagnetic order ( TN=6 K) with an ordered moment of only 0.02 μB/U atom is believed to play a crucial role in the existence of multiple superconducting phases, as it can act as a symmetry-breaking field for the vector order parameter of the unconventional superconductivity. We review recent progress in neutron scattering measurements on the weak antiferromagnetic order as a function of magnetic field, pressure, and Pd doping and on the superconducting flux-line lattice. The relation between the magnetic and superconducting properties is discussed.

  1. Uniaxial pressure dependence of the antiferromagnetic order in UPt{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Dijk, N.H. van [IRI, NM, TU Delft, Mekelweg 15, 2629 JB Delft (Netherlands); Rodiere, P.; Huxley, A.; Flouquet, J. [DRFMC, SPSMS, CEA/Grenoble, 17 rue des Martyrs, 38054 Grenoble (France); Faak, B. [DRFMC, SPSMS, CEA/Grenoble, 17 rue des Martyrs, 38054 Grenoble (France); ISIS, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX (United Kingdom); Fernandez-Diaz, M.T. [ILL, BP 156, 38042 Grenoble Cedex (France); Yakhou, F. [ESRF, BP 220, 38043 Grenoble Cedex (France)

    2002-07-01

    The weak antiferromagnetic order of the heavy-fermion superconductor UPt{sub 3} has been investigated by elastic neutron-scattering measurements under applied uniaxial pressure up to 6 kbar along the a and c axes of the hexagonal crystal structure. For p parallel c the small antiferromagnetically ordered moment of 0.02 {mu}{sub B}/U-atom shows a non-linear decrease for increasing pressures and is still not completely suppressed at the maximum applied pressure of 6 kbar. For p parallel a a significant increase in the magnetic Bragg peak intensity is observed, which suggests an incomplete domain repopulation and confirms the presence of a single-k structure. (orig.)

  2. Easy moment direction and antiferromagnetic domain wall motion in Mn{sub 2}Au

    Energy Technology Data Exchange (ETDEWEB)

    Barthem, Vitoria M.T.S. [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Cidade Universitaria, Ilha do Fundao, 21941-972 Rio de Janeiro (Brazil); Colin, Claire V.; Haettel, Richard; Dufeu, Didier [Université Grenoble Alpes, Institut NEEL, 25 Avenue des Martyrs, BP 166, F-38042 Grenoble (France); CNRS, Institut NEEL, 25 Avenue des Martyrs, BP 166, F-38042 Grenoble (France); Givord, Dominique, E-mail: dominique.givord@neel.cnrs.fr [Instituto de Fisica, Universidade Federal do Rio de Janeiro, Cidade Universitaria, Ilha do Fundao, 21941-972 Rio de Janeiro (Brazil); Université Grenoble Alpes, Institut NEEL, 25 Avenue des Martyrs, BP 166, F-38042 Grenoble (France); CNRS, Institut NEEL, 25 Avenue des Martyrs, BP 166, F-38042 Grenoble (France)

    2016-05-15

    The interest of giving active functions to antiferromagnetic (AFM) materials in spintronics devices has been realized recently. Mn{sub 2}Au is a high-Néel temperature antiferromagnet with large Mn moment, lying in plane of the tetragonal structure. To determine the direction of the moments in Mn{sub 2}Au, an original approach is demonstrated, which should be generic to planar AFM materials. It involves the rotation of the granular sample around an axis perpendicular to the applied magnetic field. The family of easy moment directions is 〈110〉. For grains prevented from rotating, the dominant magnetization process is AFM domain wall motion. Textured Mn{sub 2}Au nanoelements could be introduced in spintronics devices, in which the Mn moments would be switched under modest external excitation.

  3. Integration of antiferromagnetic Heusler compound Ru2MnGe into spintronic devices

    Science.gov (United States)

    Balluff, Jan; Huminiuc, Teodor; Meinert, Markus; Hirohata, Atsufumi; Reiss, Günter

    2017-07-01

    We report on the integration of an antiferromagnetic Heusler compound acting as a pinning layer into magnetic tunneling junctions (MTJs). The antiferromagnet Ru2MnGe is used to pin the magnetization direction of a ferromagnetic Fe layer in MgO based thin film tunneling magnetoresistance stacks. The samples were prepared using magnetron co-sputtering. We investigate the structural properties by X-ray diffraction and reflection, as well as atomic force and high-resolution transmission electron microscopy. We find an excellent crystal growth quality with a low interface roughnesses of 1-3 Å, which is crucial for the preparation of working tunneling barriers. Using Fe as a ferromagnetic electrode material, we prepared magnetic tunneling junctions and measured the magnetoresistance. We find a sizeable maximum magnetoresistance value of 135%, which is comparable to other common Fe based MTJ systems.

  4. Solution of the antiferromagnetic Ising model on a tetrahedron recursive lattice.

    Science.gov (United States)

    Jurčišinová, E; Jurčišin, M

    2014-03-01

    We consider the antiferromagnetic spin-1/2 Ising model on the recursive tetrahedron lattice on which two elementary tetrahedrons are connected at each site. The model represents the simplest approximation of the antiferromagnetic Ising model on the real three-dimensional tetrahedron lattice which takes into account effects of frustration. An exact analytical solution of the model is found and discussed. It is shown that the model exhibits neither the first-order nor the second-order phase transitions. A detailed analysis of the magnetization of the model in the presence of the external magnetic field is performed and the existence of the magnetization plateaus for low temperatures is shown. All possible ground states of the model are found and discussed. The existence of nontrivial singular ground states is proven and exact explicit expressions for them are found.

  5. The antiferromagnetic cross-coupled spin ladder: Quantum fidelity and tensor networks approach

    Science.gov (United States)

    Chen, Xi-Hao; Cho, Sam Young; Zhou, Huan-Qiang; Batchelor, Murray T.

    2016-05-01

    We investigate the phase diagram of the cross-coupled Heisenberg spin ladder with antiferromagnetic couplings. For this model, the results for the existence of the columnar dimer phase, which was predicted on the basis of weak coupling field theory renormalization group arguments, have been conflicting. The numerical work on this model has been based on various approaches, including exact diagonalization, series expansions and density-matrix renormalization group calculations. Using the recently-developed tensor network states and groundstate fidelity approach for quantum spin ladders, we find no evidence for the existence of the columnar dimer phase. We also provide an argument based on the symmetry of the Hamiltonian, which suggests that the phase diagram for antiferromagnetic couplings consists of a single line separating the rung-singlet and the Haldane phases.

  6. Field-Induced Multiple Reentrant Quantum Phase Transitions in Randomly Dimerized Antiferromagnetic S=1/2 Heisenberg Chains

    Science.gov (United States)

    Hida, Kazuo

    2006-07-01

    The multiple reentrant quantum phase transitions in the S=1/2 antiferromagnetic Heisenberg chains with random bond alternation in the magnetic field are investigated by the density matrix renormalization group method combined with interchain mean field approximation. It is assumed that odd numbered bonds are antiferromagnetic with strength J and even numbered bonds can take the values JS and JW (JS > J > JW > 0) randomly with the probabilities p and 1- p, respectively. The pure version ( p=0 and 1) of this model has a spin gap but exhibits a field-induced antiferromagnetism in the presence of interchain coupling if Zeeman energy due to the magnetic field exceeds the spin gap. For 0 < p < 1, antiferromagnetism is induced by randomness at the small field region where the ground state is disordered due to the spin gap in the pure version. At the same time, this model exhibits randomness-induced plateaus at several values of magnetization. The antiferromagnetism is destroyed on the plateaus. As a consequence, we find a series of reentrant quantum phase transitions between transverse antiferromagnetic phases and disordered plateau phases with the increase of magnetic field for a moderate strength of interchain coupling. Above the main plateaus, the magnetization curve consists of a series of small plateaus and jumps between them. It is also found that antiferromagnetism is induced by infinitesimal interchain coupling at the jumps between the small plateaus. We conclude that this antiferromagnetism is supported by the mixing of low-lying excited states by the staggered interchain mean field even though the spin correlation function is short ranged in the ground state of each chain.

  7. Electric field modulation of tunneling anisotropic magnetoresistance in tunnel junctions with antiferromagnetic electrodes

    Science.gov (United States)

    Goto, Minori; Nawaoka, Kohei; Miwa, Shinji; Hatanaka, Shohei; Mizuochi, Norikazu; Suzuki, Yoshishige

    2016-08-01

    We present electric field modulation of tunneling anisotropic magnetoresistance (TAMR) in MnIr|MgO|Ta tunnel junctions. TAMR enables direct observation of the antiferromagnetic spin direction at the MnIr|MgO interface. We found that the shape of magnetoresistance (MR) curve can be modulated by an electric field, which can be explained by electric field modulation of the interfacial magnetic anisotropy at MnIr|MgO.

  8. Study of the Antiferromagnetic Blume-Capel Model on kagomé Lattice

    Science.gov (United States)

    Hwang, Chi-Ok; Park, Sojeong; Kwak, Wooseop

    2016-09-01

    We study the anti-ferromagnetic (AF) Ising model and the AF Blume-Capel (BC) model on the kagomé lattice. Using the Wang-Landau sampling method, we estimate the joint density functions for both models on the lattice, and we obtain the exact critical magnetic fields at zero temperature by using the micro-canonical analysis. We also show the patterns of critical lines for the models from micro-canonical analysis.

  9. Phase transition in Heisenberg stacked triangular antiferromagnets: end of a controversy.

    Science.gov (United States)

    Ngo, V Thanh; Diep, H T

    2008-09-01

    By using the Wang-Landau flat-histogram Monte Carlo (MC) method for very large lattice sizes never simulated before, we show that the phase transition in the frustrated Heisenberg stacked triangular antiferromagnet is of first order, contrary to results of earlier MC simulations using old-fashioned methods. Our result lends support to the conclusion of a nonperturbative renormalization group performed on an effective Hamiltonian. It puts an end to a 20-year -long controversial issue.

  10. Monte Carlo Study of the Anisotropic Heisenberg Antiferromagnet on the Triangular Lattice

    OpenAIRE

    Stephan, W.; Southern, B. W.

    1999-01-01

    We report a Monte Carlo study of the classical antiferromagnetic Heisenberg model with easy axis anisotropy on the triangular lattice. Both the free energy cost for long wavelength spin waves as well as for the formation of free vortices are obtained from the spin stiffness and vorticity modulus respectively. Evidence for two distinct Kosterlitz-Thouless types of defect-mediated phase transitions at finite temperatures is presented.

  11. Susceptibility of the 2D spin-1 / 2 Heisenberg antiferromagnet with an impurity.

    Science.gov (United States)

    Höglund, Kaj H; Sandvik, Anders W

    2003-08-15

    We use a quantum Monte Carlo method (stochastic series expansion) to study the effects of a magnetic or nonmagnetic impurity on the magnetic susceptibility of the two-dimensional Heisenberg antiferromagnet. At low temperatures, we find a log-divergent contribution to the transverse susceptibility. We also introduce an effective few-spin model that can quantitatively capture the differences between magnetic and nonmagnetic impurities at high and intermediate temperatures.

  12. Correlation functions of the antiferromagnetic Heisenberg model using a modified Lanczos method

    Science.gov (United States)

    Gagliano, Eduardo R.; Dagotto, Elbio; Moreo, Adriana; Alcaraz, Francisco C.

    1986-08-01

    Using a modified Lanczos algorithm, we study the correlation functions in the ground state of the one-dimensional antiferromagnetic Heisenberg model. We obtain numerical results for rings up to 24 sites. There are no indications of the anomalous behavior of these correlation functions recently observed in chains with 16 sites. We also present a pedagogical description of the hashing technique which is an efficient algorithm for searching and storage purposes.

  13. Spin transport of the frustrated integer spin S antiferromagnetic Heisenberg chain

    Energy Technology Data Exchange (ETDEWEB)

    Lima, Leonardo S., E-mail: lslima@infis.ufu.br [Instituto de Física, Universidade Federal de Uberlândia, UFU, CEP:38700-128, Patos de Minas, MG (Brazil); Departamento de Física, ICEx, Universidade Federal de Minas Gerais, CEP:31270-901, Belo Horizonte, MG (Brazil)

    2014-03-15

    We study the effect of the nearest-neighbor (nn) and next-nearest-neighbor (nnn) interactions on spin transport in the quantum integer spin one-dimensional isotropic antiferromagnetic Heisenberg model. The Kubo formalism of the linear response theory is used to calculate the spin conductivity. We obtain the regular part of the spin conductivity, σ{sup reg}(ω), as function of the frequency at T=0 and obtain a strong effect of the (nnn) interaction on magnon transport.

  14. Enhancement of antiferromagnetic spin wave in the heavy-fermion superconductors

    Science.gov (United States)

    Koh, Shun-ichiro

    2000-06-01

    Recently, the inelastic neutron scattering experiments of UPd 2Al 3 showed that a sharp peak indicating a magnetic excitation appears below the superconducting phase transition temperature (M. Metoki et al., J. Phys. Soc. Japan 66 (1997) 2560, N. Bernhoeft et al., Phys. Rev. Lett. 81 (1998) 4244). Assuming this excitation to be an antiferromagnetic (AFM) spin wave, this paper deals with its enhancement by the superconductivity.

  15. Spin flop in one-dimensional Heisenberg antiferromagnet KCuF3

    Institute of Scientific and Technical Information of China (English)

    Shi Qing-Fan; Li Liang-Sheng; Wang Qi

    2004-01-01

    Following Yamada and Karo [J. Phys. Soc. Japan 63 (1994) 289], we have calculated the frequency-field diagram of antiferromagnetic resonance of KCuF3 using an eight-sublattice model and mean field approximation. A spin flop is found to take place from the [110]p to a direction perpendicular to [110]p in the c-plane at H≌ 42172A-m, which is in good agreement with the data obtained by measuring magnetic susceptibility.

  16. Spin flop in one-dimensional Heisenberg antiferromagnet KCuF3

    Science.gov (United States)

    Shi, Qing-Fan; Li, Liang-Sheng; Wang, Qi

    2004-04-01

    Following Yamada and Kato [J. Phys. Soc. Japan 63 (1994) 289], we have calculated the frequency-field diagram of antiferromagnetic resonance of KCuF3 using an eight-sublattice model and mean field approximation. A spin flop is found to take place from the [110]p to a direction perpendicular to [110]p in the c-plane at Hsimeq 42172A/m, which is in good agreement with the data obtained by measuring magnetic susceptibility.

  17. Imaging and Control of Surface Magnetization Domains in a Magnetoelectric Antiferromagnet

    Science.gov (United States)

    Wu, Ning; He, Xi; Wysocki, Aleksander L.; Lanke, Uday; Komesu, Takashi; Belashchenko, Kirill D.; Binek, Christian; Dowben, Peter A.

    2011-02-01

    We report the direct observation of surface magnetization domains of the magnetoelectric Cr2O3 using photoemission electron microscopy with magnetic circular dichroism contrast and magnetic force microscopy. The domain pattern is strongly affected by the applied electric field conditions. Zero-field cooling results in an equal representation of the two domain types, while electric-field cooling selects one dominant domain type. These observations confirm the existence of surface magnetization, required by symmetry in magnetoelectric antiferromagnets.

  18. Antiferromagnetic ordering in superconducting YBa2Cu3O6.5

    DEFF Research Database (Denmark)

    Sidis, Y.; Ulrich, C.; Bourges, P.

    2001-01-01

    Commensurate antiferromagnetic ordering has been observed in the superconducting high-T-c. cuprate YBa2Cu3O6.5 (T-c = 55 K) by polarized and unpolarized elastic neutron scattering. The magnetic peak intensity exhibits a marked enhancement at T-c. Zero-field muon-spin-resonance experiments...... demonstrate that the staggered magnetization is not truly static but fluctuates on a nanosecond time scale. These results point towards an unusual spin density wave state coexisting with superconductivity....

  19. Electrical Control of Antiferromagnetic Domains in Multiferroic BiFeO3 Films at Room Temperature

    Science.gov (United States)

    2006-09-03

    Source, Lawrence Berkeley National Lab, Berkeley, California 94720, USA 3Centro de Ciencias de la Materia Condensada (CCMC)-UNAM Km 107, Carretera...b. ABSTRACT unclassified c. THIS PAGE unclassified Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18 ARTICLES O Fe Bi 18 0° 109° 71...antiferromagnetic ordering is G-type; that is nearest- neighbour Fe moments are aligned antiparallel to each other in all three cartesian directions13. In bulk

  20. su(1,2) Algebraic Structure of XYZ Antiferromagnetic Model in Linear Spin-Wave Frame

    Institute of Scientific and Technical Information of China (English)

    GUAN Yong; JIN Shuo; LIN Bing-Sheng; XIE Bing-Hao; JING Si-Cong; YU Zhao-Xian; HOU Jing-Min

    2008-01-01

    The XYZ antiferromagnetic model in linear spin-wave frame is shown explicitly to have an su(1,2) aigebraic structure: the Hamiltonian can be written as a linear function of the su(1,2) algebra generators. Based on it, the energy eigenvalues are obtained by making use of the similar transformations, and the algebraic diagonalization method is investigated. Some numerical solutions are given, and the results indicate that only one group solution could be accepted in physics.