176 research outputs found

    Phase Diagram of the Dzyaloshinskii-Moriya Helimagnet Ba2CuGe2O7 in Canted Magnetic Fields

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    The evolution of different magnetic structures of non-centrosymmetric Ba2CuGe2O7 is systematically studied as function of the orientation of the magnetic field H. Neutron diffraction in combination with measurements of magnetization and specific heat show a virtually identical behaviour of the phase diagram of Ba2CuGe2O7 for H confined in both the (1,0,0) and (1,1,0) plane. The existence of a recently proposed incommensurate double-k AF-cone phase is confirmed in a narrow range for H close to the tetragonal c-axis. For large angles enclosed by H and the c-axis a complexely distorted non-sinusoidal magnetic structure has recently been observed. We show that its critical field Hc systematically increases for larger canting. Measurements of magnetic susceptibility and specific heat finally indicate the existence of an incommensurate/commensurate transition for H /sim 9 T applied in the basal (a,b)-plane and agree with a non-planar, distorted cycloidal magnetic structure.Comment: 14 pages, 13 figure

    Cooperative ordering of gapped and gapless spin networks in Cu2_2Fe2_2Ge4_4O13_{13}

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    The unusual magnetic properties of a novel low-dimensional quantum ferrimagnet Cu2_2Fe2_2Ge4_4O13_{13} are studied using bulk methods, neutron diffraction and inelastic neutron scattering. It is shown that this material can be described in terms of two low-dimensional quantum spin subsystems, one gapped and the other gapless, characterized by two distinct energy scales. Long-range magnetic ordering observed at low temperatures is a cooperative phenomenon caused by weak coupling of these two spin networks.Comment: 4 pages, 4 figure

    Switching of the magnetic order in CeRhIn5‚ąíx_{5-x}Snx_{x} in the vicinity of its quantum critical point

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    We report neutron diffraction experiments performed in the tetragonal antiferromagnetic heavy fermion system CeRhIn5‚ąíx_{5-x}Snx_{x} in its (xx, TT) phase diagram up to the vicinity of the critical concentration xcx_c ‚Čą\approx 0.40, where long range magnetic order is suppressed. The propagation vector of the magnetic structure is found to be kIC\bf{k_{IC}}=(1/2, 1/2, klk_l) with klk_l increasing from klk_l=0.298 to klk_l=0.410 when xx increases from xx=0 to xx=0.26. Surprisingly, for xx=0.30, the order has changed drastically and a commensurate antiferromagnetism with kC\bf{k_{C}}=(1/2, 1/2, 0) is found. This concentration is located in the proximity of the quantum critical point where superconductivity is expected.Comment: 5 pages, 5 figures, submitted to Phys. Rev.

    Magnetic frustration in an iron based Cairo pentagonal lattice

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    The Fe3+ lattice in the Bi2Fe4O9 compound is found to materialize the first analogue of a magnetic pentagonal lattice. Due to its odd number of bonds per elemental brick, this lattice, subject to first neighbor antiferromagnetic interactions, is prone to geometric frustration. The Bi2Fe4O9 magnetic properties have been investigated by macroscopic magnetic measurements and neutron diffraction. The observed non-collinear magnetic arrangement is related to the one stabilized on a perfect tiling as obtained from a mean field analysis with direct space magnetic configurations calculations. The peculiarity of this structure arises from the complex connectivity of the pentagonal lattice, a novel feature compared to the well-known case of triangle-based lattices

    Kagom\'{e} ice state in the dipolar spin ice Dy_{2}Ti_{2}O_{7}

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    We have investigated the kagom\'{e} ice behavior of the dipolar spin-ice compound Dy_{2}Ti_{2}O_{7} in magnetic field along a [111] direction using neutron scattering and Monte Carlo simulations. The spin correlations show that the kagom\'{e} ice behavior predicted for the nearest-neighbor (NN) interacting model, where the field induces dimensional reduction and spins are frustrated in each two-dimensional kagom\'{e} lattice, occurs in the dipole interacting system. The spins freeze at low temperatures within the macroscopically degenerate ground states of the NN model.Comment: 5 pages, 3 figures, submitted to PR

    Half-ordered state in the anisotropic Haldane-gap antiferromagnet NDMAP

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    Neutron diffraction experiments performed on the Haldane gap material NDMAP in high magnetic fields applied at an angle to the principal anisotropy axes reveal two consecutive field-induced phase transitions. The low-field phase is the gapped Haldane state, while at high fields the system exhibits 3-dimensional long-range Neel order. In a peculiar phase found at intermediate fields only half of all the spin chains participate in the long-range ordering, while the other half remains disordered and gapped.Comment: 4 pages, 2 figures, submitted to Phys. Rev.

    Single domain magnetic helicity and triangular chirality in structurally enantiopure Ba3NbFe3Si2O14

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    A novel doubly chiral magnetic order is found out in the structurally chiral langasite compound Ba3_3NbFe3_3Si2_2O14_{14}. The magnetic moments are distributed over planar frustrated triangular lattices of triangle units. On each of these they form the same triangular configuration. This ferro-chiral arrangement is helically modulated from plane to plane. Unpolarized neutron scattering on a single crystal associated with spherical neutron polarimetry proved that a single triangular chirality together with a single helicity is stabilized in an enantiopure crystal. A mean field analysis allows discerning the relevance on this selection of a twist in the plane to plane supersuperexchange paths
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