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Now showing 1 - 10 of 58
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    Composite domain walls in flat nanomagnets: the magnetostatic limit
    Youk, H.; Chern, G.-W.; Merit, K.; Oppenheimer, B.; Tchernyshyov, O. (American Institute of Physics, 2006-04-15)
    We discuss the structure of the so-called 'vortex' domain walls in soft magnetic nanoparticles. A wall of this kind is a composite object consisting of three elementary topological defects: two edge defects with winding numbers -1/2 and a vortex with a winding number +1 between them. We provide a qualitative model accounting for the energetics of such a domain wall.
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    Direct transition from a disordered to a multiferroic phase on a triangular lattice
    Kenzelmann, M.; Lawes, G.; Harris, A. B.; Gasparovic, G.; Broholm, C.; Ramirez, A. P.; Jorge, G.A.; Jaime, M.; Park, S.; Huang, Q.; Shapiro, A. Y.; Demianets, L. A. (American Physical Society, 2007-06-29)
    We report the first direct transition from a paramagnetic and paraelectric phase to an incommensurate multiferroic in the triangular lattice antiferromagnet RbFe(MoO4)2. Ferroelectricity is observed only when the magnetic structure has chirality and breaks inversion symmetry. A Landau expansion of symmetry-allowed terms in the free energy demonstrates that chiral magnetic order can give rise to a pseudoelectric field, whose temperature dependence agrees with experiment.
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    Exploiting finite size effects in a novel core/shell microstructure
    Liu, Zhu; Xia, Guoqiang; Zhu, Frank; Kim, Su; Markovic, Nina; Chien, Chia-Ling; Searson, Peter C. (American Institute of Physics, 2008-03-15)
    Electrodeposition of Ni-Cu alloys at high Cu(II) concentration and large overpotentials results in phase separation with a unique microstructure characterized by features with a copper-rich core and a nickel-rich shell. By confining deposition to nanoporous channels with dimensions comparable to or smaller than the grain size results in the formation of solid Ni-Cu nanowires with a copper-rich core and a nickel-rich shell. Etching of the copper-rich core results in the formation of Ni-rich nanotubes. The magnetic properties of the Ni-Cu nanowires and the Ni nanotubes are investigated.
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    Condensation of magnons and spinons in a frustrated ladder
    Fouet, J.-B.; Mila, F.; Clarke, D.; Youk, H.; Tchernyshyov, O.; Fendley, P.; Noack, R. M. (American Physical Society, 2006-06-01)
    Motivated by the ever-increasing experimental effort devoted to the properties of frustrated quantum magnets in a magnetic field, we present a careful and detailed theoretical analysis of a one-dimensional version of this problem, a frustrated ladder with a magnetization plateau at m=1/2. We show that even for purely isotropic Heisenberg interactions, the magnetization curve exhibits a rather complex behavior that can be fully accounted for in terms of simple elementary excitations. The introduction of anisotropic interactions (e.g., Dzyaloshinskii-Moriya interactions) modifies significantly the picture and reveals an essential difference between integer and fractional plateaus. In particular, anisotropic interactions generically open a gap in the region between the plateaus, but we show that this gap closes upon entering fractional plateaus. All of these conclusions, based on analytical arguments, are supported by extensive density matrix renormalization group calculations.
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    Neutron scattering from a coordination polymer quantum paramagnet
    Hong, T.; Kenzelmann, M.; Turnbull, M. M.; Landee, C. P.; Lewis, B.D.; Schmidt, K. P.; Uhrig, G. S.; Broholm, C.; Reich, D. (American Physical Society, 2006-09-01)
    Inelastic neutron scattering measurements are reported for a powder sample of the spin-1/2 quantum paramagnet Cu(quinoxaline)Br2. Magnetic neutron scattering is identified above an energy gap of 1.9 meV. Analysis of the sharp spectral maximum at the onset indicates that the material is magnetically quasi-one-dimensional. Consideration of the wave vector dependence of the scattering and polymeric structure further identifies the material as a two-legged spin-1/2 ladder. Detailed comparisons of the data to various models of magnetism in this material based on the single-mode approximation and the continuous unitary transformation are presented. The latter theory provides an excellent account of the data with leg exchange J∥=2.0 meV and rung exchange J⊥=3.3 meV.
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    Neutron scattering evidence for isolated spin-1/2 ladders in (C5D12N)2CuBr4
    Nagler, S. E.; Pajerowski, D. M.; Meisel, M. W.; Broholm, C.; Schmidt, K. P.; Talham, D. R.; Brown, C.M.; Uhrig, G. S.; Savici, A.T.; Granroth, G. E. (American Physical Society, 2009-09-01)
    Inelastic neutron scattering was used to determine the spin Hamiltonian for the singlet ground-state system of fully deuterated BPCB, (C5D12N)2CuBr4. A two-leg spin-1/2 ladder model, with J⊥=(1.09±0.01) meV and J∥=(0.296±0.005) meV, accurately describes the data. The experimental limit on the effective interladder exchange constant is |Jinteff|≤0.006 meV, and the limit on total diagonal, intraladder exchange is |JF+JF'|≤0.1 meV. Including the effects of copper to bromide covalent spin transfer on the magnetic form factor, the experimental ratios of intraladder bond energies are consistent with the predictions of continuous unitary transformation.
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    Inhomogeneous level splitting in Pr2-xBixRu2O7
    van Duijn, J.; Kim, K. H.; Hur, N.; Adroja, D.; Adams, M. A.; Huang, Q.Z.; Jaime, M.; Cheong, S.-W.; Broholm, C.; Perring, T.G. (American Physical Society, 2005-05-06)
    We report that Bi doping drives Pr2-xBixRu2O7 from an antiferromagnetic insulator (x=0) to a metallic paramagnet (x≈1) with a broad low T maximum in C/T. Neutron scattering reveals local low energy spin excitations (ℎω≈1 meV) with a spectrum that is unaffected by heating to kBT>>ℎω. We show that a continuous distribution of splittings of the non-Kramers Pr3+ ground-state doublet such as might result from various types of lattice strain can account for all the data.
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    Magnetic core loss of ultrahigh strength FeCo alloys
    Cheng, X.M.; Zhang, X.K.; Zhang, D.Z.; Lee, S.H.; Duckham, A.; Weihs, T. P.; Cammarata, R.C.; Chien, C.-L. (American Institute of Physics, 2003-05-15)
    Hiperco® 50 alloy heat treated between 450 and 650°C exhibits superior mechanical properties. We report the measurements of the ac core loss at various frequencies up to 4500 Hz of the Hiperco® 50 alloy samples annealed at 450 and 650°C. The 650°C annealed specimens have lower ac core loss than that of the 450°C annealed ones. The total core loss, consisting of contributions from hysteresis core loss and eddy-current core loss, depends on frequency f as af+bf2. The eddy-current loss of a single laminate is minor compared to the hysteresis loss.
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    Cell manipulation using magnetic nanowires
    Hultgren, A.; Tanase, M.; Chen, C. S.; Meyer, G. J.; Reich, D.H. (American Institute of Physics, 2003-05-15)
    The use of magnetic nanowires is demonstrated as a method for the application of force to mammalian cells. Magnetic separations were carried out on populations of NIH-3T3 mouse fibroblast cells using ferromagnetic Ni wires 350 nm in diameter and 35 μm long. Separation purities in excess of 90% and yields of 49% are obtained. The nanowires are shown to outperform magnetic beads of comparable volume.
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    Doubly exchange-biased NiCoO/NiFe/Cu/NiFe/NiCoO spin valves
    Ambrose, T.; Liu, K.; Chien, C.-L. (American Institute of Physics, 1999-04-15)
    A new type of doubly exchange-biased Ni50Co50O/NiFe/Cu/NiFe/Ni30Co70O spin-valve structure, with two ferromagnetic layers exchange biased in opposite directions by two different antiferromagnetic layers is demonstrated. By field cooling in magnetic fields of opposite directions, the resultant hysteresis loop consists of two loops shifted in opposite directions from the zero magnetic field. The NiFe layers are in the antiparallel state in zero magnetic field, and the switching to the parallel state can be tuned by varying the exchange bias. The modified spin valves also show potential for suppressed Barkhausen noise.