A quantum magnet, LiCuSbO 4 , with chains of edge-sharing spin-½ CuO 6 octahedra is reported. While short-range order is observed for T < 10 K, no zero-field phase transition or spin freezing occurs down to 100 mK. Specific heat indicates a distinct high field phase near the 12 T saturation field. Neutron scattering shows incommensurate spin correlations with q = (0.47±0.01)π/a and places an upper limit of 70 µeV on any spin gap. Exact diagonalization of 16-spin easy-plane spin-½ chains with competing ferro-and antiferromagnetic interactions (J 1 = -75 K, J 2 = 34 K) accounts for the T > 2 K data. PACS: 75.10.Jm, 75.30.Kz, 75.40.Cx, 75.30.Et 2 The Heisenberg spin-½ chain is one of very few quantum critical systems to be realized in a crystalline solid. An element of frustration is added by next-nearest-neighbor (NNN) interactions (J 2 ). [1][2][3] In such systems, theoretical work [4][5][6][7][8][9] indicates that qualitatively different quantum phases are possible as a function of α = J 2 /J 1 , axial exchange anisotropy, ∆, and the applied field h = gµ B H/|J 1 |. Finite values of α are observed in copper oxide spin-chains formed by corner-or edge-sharing Jahn-Teller distorted CuO 6 polyhedra. [10][11][12][13][14][15][16][17] While the sign and magnitude of J 1 is dependent on the α c ) from a short-range ordered (SRO) phase with a small yet finite gap (α < α c ). 20Dimer, spiral, vector-chiral and multipolar phases have been predicted as a function of α, ∆ and h. 4,6,8 Interest has been further amplified by the observation that ferroelectricity accompanies magnetic ordering in some of these systems. 14,21,22 Known spin-½ FM-AFM chains span a wide range of α and include Li 2 CuO 2 , 17,21,22 Here we present the structure and magnetic properties of the one-dimensional (1D) spin chain compound LiCuSbO 4 . Due to weak inter-chain interactions it has no 3D ordering down to 100 mK and can be driven to a saturated-FM phase above the experimentally accessible field <µ o H s > = 12 T. The magnetic susceptibility, isothermal magnetization and specific heat can be simultaneously modelled for T > 2 K using the approximate spin Hamiltonian:Here θ is the angle between the applied field, h, and the unique molecular axis, z. The parameters J 1 = -75K, α = -0.45, and ∆ = 0.83 account for the main features in the thermomagnetic data and are also consistent with the magnetic excitations measured by inelastic neutron scattering.Powder samples of LiCuSbO 4 were prepared using a ceramic synthesis. 25LiCuSbO 4 has an orthorhombic structure 26, 27 related to that of LiFeSnO 4 . 28Rietveld analysis 29 of powder neutron diffraction data acquired on the BT1 diffractometer at NIST 30 was carried out using FULLPROF. 31The final fit, with the corr...

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The crystal structures of two Delafossites, Cu3Ni2SbO6 and Cu3Co2SbO6, are determined by high-resolution synchrotron powder X-ray diffraction. The Ni and Co are ordered with respect to Sb in the layer of edge sharing octahedra, forming magnetic layers with honeycomb geometry. High-resolution electron microscopy confirms ordering, and selected-area electron diffraction patterns identify examples of the stacking polytypes. Low temperature synthetic treatments result in disordered stacking of the layers, but heating just below their melting points results in nearly fully ordered stacking variants. The major variant in both cases is a monoclinic distortion of a 6-layer Delafossite polytype, but a significant amount of a 2-layer polytype is also present for the Ni case. The antiferromagnetic ordering with transitions, at 22.3 and 18.5 K for Ni and Co variants, respectively, is investigated by temperature and field dependent magnetization, as well as specific heat. The sharp magnetic transitions support the presence of well developed 2:1 ordering of the Co:Sb or Ni:Sb ions in the honeycomb layers. Neutron diffraction measurements at 4 K are used to determine the magnetic structures. For both the Ni and Co phases, the propagation vector is k = [100], and can be described as alternating ferromagnetic chains in the metal-oxide plane giving an overall antiferromagntic "zigzag" alignment. While orientation of the magnetic moments of the Co is along the b-axis, the Ni moments are in the ac plane, approximately parallel to the stacking direction. Bulk magnetization properties are discussed in terms of their magnetic structures.

We report significant details of the magnetic structure and spin dynamics of LiFePO4 by single crystal neutron scattering. Our results confirm a previously reported co-linear rotation of the spins away from the principal b axis and determine that the rotation is towards the a axis. In addition, we find a significant spin canting component along c. The possible causes of these components are discussed and their significance for the magneto-electric (ME) effect is analyzed. Inelastic neutron scattering along the three principal directions reveal a highly anisotropic hard plane consistent with earlier susceptibility measurements. Using a spin Hamiltonian, we show that the spin-dimensionality is intermediate between XY-and Ising-like, with an easy b axis and hard c axis. It is shown that both next-nearest neighbour (NNN) exchange couplings in the bc plane are in competition with the strongest nearest neighbour (NN) coupling.