Perpendicular Chains Research Articles

Selectively "size-excluding" water molecules to enable a highly reversible zinc metal anode.

Significant water-related side reactions hinder the development of highly safe, low-cost aqueous zinc metal batteries (AZMBs) for grid-scale energy storage. Herein, by regulating the length of alkyl chains, we successfully adjust interstitial voids between the polymer chains of a metal soap interface between 1.48 Å (size of a zinc ion) and 4.0 Å (size of a water molecule). Therefore, water molecules are selectively "size-excluded," while smaller zinc ions are permitted to pass through. Consequently, water-related side reactions (including hydrogen evolution and corrosion) could be effectively inhibited. Furthermore, abundant zinc ion tunnels accompanied with zincophilic components facilitate the homogenization of the Zn2+ flux, thus preventing dendrite growth. Therefore, the Zn symmetric cell shows a lifespan of approximately 10 000 cycles at 20 mA cm-2 and 1 mA h cm-2, and the Zn//Na5V12O32 (NVO) full cell delivers much better cycling stability with much higher capacity retention of around 93% after 2000 cycles at 2 A g-1 compared to its bare Zn counterpart (19%). This work provides valuable insights for the utilization of metal soap interfaces and regulation of their channel size between perpendicular alkyl chains to realize precise water shielding, which is not only applicable in ZMBs but also in other aqueous batteries.

Synthesis of Blend Polymer (PVA / PANI)/Copper (1) Oxide Nanocomposite: Thermal Analysis and UV-Vis Spectra Specifications

Copper (1) oxide nanoparticles together with matrix polymers of polyvinyl alcohol (PVA) and polyaniline (PANI) composite films were synthesized, as these materials are of importance in optoelectronic applications. ‎Nanoparticles of Cu2O were produced by chemical precipitation. Polymerization of aniline was carried out through polymerization in an acidic medium. Structural, thermal, and optical properties of PVA+PANI/Cu2O nanocomposite were inspected by x-ray diffraction (XRD), scanning electron microscopy (SEM), fourier-transform infrared (FTIR), differential scanning calorimeter (DSC) and ultraviolet-visible spectroscopy (UV-Vis spectroscopy). X-ray diffraction peaks at 29.53°, 36.34°, and 42.22° indicated the presence of cuprous oxide nanoparticles, having high dispersions and limited size distributions. The estimated average size of Cu2O nanoparticles was ~ 17.1525 nm. A characteristic peak at around 2θ = 18.5° was attributed to periodical parallel and perpendicular polymer chains, which denoted the formation of PANI. SEM results indicated the symmetrical dispersion of Cu2O nanoparticles inside the hybrid polymer of PVA and PANI matrix, being potentially useful for encapsulation and acting as a good capping agent. FTIR results established the formation of PANI and Cu2O with nanocrystalline nature. DSC results revealed the appearance of one single peak of Tg which decreased with Cu2O content of 4% wt, followed by an increase of that value by increasing Cu2O content up to 16%wt. Thermogram analysis of the PANI and PVA embedded with Cu2O form showed an exothermic peak at (240-292)℃ affiliated to the cross-linking reaction, while the Tm value of prepared nanocomposites is just about close to that of PVA polymer. The results indicated that there is an increase in thermal stability due to the presence of Cu2O NPS within the matrix of polymers. The distinguishing peaks at 330, 347, and 457 nm which refer to PANI are assigned to π−π* electron transitions among the benzenoid rings. The high absorption intensity of the peak at 470 nm for the blended PVA+PANI having 12% wt of Cu2O NPS is assigned due to the inter-band transitions for electrons of the core copper as well as copper oxide. This points out that the increasing quantity of Cu2O NPs leads to increases in the amounts of highly oxidized structures in PANI and decreases in the doping electrons and length of conjugation throughout the incorporation of Cu2O NPs into PANI matrix. Depending on the practical results, it can be said that these polymeric nanocomposites can be efficiently used in photovoltaic technology applications.

Spin-orbit coupling controlling the topological vortical phase transition in spin-2 rotating Bose-Einstein condensates

We investigate the combined effects of spin-orbit coupling and rotation on the topological vortical phase transition in $F=2$ Bose-Einstein condensates. We find that the spin-orbit coupling can precisely manipulate the canonical atom current which is generated in the opposite direction of the gauge atom current and causes both a continuous and a discontinuous canonical angular momentum. We apply the canonical angular momentum and magnetization to reveal the emergence of novel topological excitations, such as the Anderson-Toulouse vortex as well as the vortex--dipole lattice. Especially, strong spin-orbit coupling can induce two perpendicular vortex chains. We also find that both the first-order and the second-order phase transition can be characterized by the canonical angular momentum and the magnetization. Differently from the spin singlet-pairing interaction, the spin-exchange interaction can adjust the canonical angular momentum and control the phase transition well. The topological vortical phase transition in an $F=2$ cold-atom system is compatible with the current experiment and can be detected by the spin polarization procedure.

Anisotropic alloying: Formation of atomic scale trellis on the Si(100)-(2 × 1) surface

Early stages of growth of two-dimensional bimetallic Ag–In islands on the Si(100)-(2 × 1) surface were studied by means of scanning tunneling microscopy. Mixing the two different metals, one forms 1D chains on the Si(100)-(2 × 1) surface and the other one creates 2D islands, results in anisotropic 2D lattice structures formed of indium chains connected by perpendicular silver chains. Growth at elevated temperatures results in more ordered structures. A model of the observed bimetallic structures and a growth scenario based on experimental data are proposed.

Crystal structure and absolute configuration of (4S,5R,6S)-4,5,6-trihy-droxy-3-methyl-cyclo-hex-2-enone (gabosine H).

The mol-ecule of the title keto carbasugar, C7H10O4, is formed by a cyclo-hexene skeleton with an envelope conformation, substituted by carbonyl, methyl and hydroxyl groups. The crystal structure is controlled mainly by a combination of strong O-H⋯O and weak C-H⋯O hydrogen bonds, forming nearly perpendicular chains running parallel to the [110] and [-110] directions. This perpendicularity is caused by a tetra-gonal pseudosymmetry influenced by the similarity between the a and b axes, the value of 90.9770 (10)° of the β angle and the action of a 21 screw axis, which transform each chain into its corresponding nearly orthogonal one.

Crankshaft chains of LEP cations as a solution to the cation size misfit

In Pb-As and Pb-Sb sulfosalts, columns of large coordination prisms of Pb combine with intervening slabs of As- or/and Sb coordination polyhedra. The LEP of these elements dictate the configurations resembling SnS (especially for As) or inflated PbS (especially for Sb). The size misfit of cation polyhedra forces the short As-S and Sb-S bonds to form crankshaft chains. In the homologues with thicker slabs, parallel crankshaft chains and incorporation of Pb in the slabs compensate for the misfit. In the low homologues, N = 3 for sartorite series and N = 4 for andorites, the misfit becomes critical and requires special arrangements. In sartorite (~PbAs2S4), two subsets of parallel short crankshaft chains in a slab are (approximately) mirror-related via two contacts. One contact has a missing S atom with valence compensation by Tl; the other one differs between the two structurally analyzed varieties, sartorite (9a) [1] and sartorite (11a) [new], which are type structures for two homologous subseries: (13a; 9a;5a) and (15a;11a;7a;3a). Structures of andorites VI and IV(~PbAgSb3S6) [2,3], and arsenquatrandorite [new] allow to construct a predictive scheme of zig-zag crankshaft chain arrangement. The 4c superstructure of andorite (IV) contains simple zig-zag sequences of As3S7 chains; in 6c andorite (VI) parallel and perpendicular chains alternate. Andorite (VI) unites, in one slab, two different stackings of perpendicular chains which are present, as separate 3c intervals, in two adjacent slabs in andorite (IV). An additional 1c interval gives the 4c structure. Further varieties, such as 10c roshchinite, are derived from these unit sequences. The fourfold varieties either have slight surplus of Pb or As replaces a part of Sb (arsenquatrandorite).

Two hydration products of 3,4,5,6-tetrachloro-N-(methyl-2-pyridyl)phthalmic acids

In 2-amino-6-methylpyridin-1-ium 2-carboxy-3,4,5,6-tetrachlorobenzoate, C(6)H(9)N(2)(+)·C(8)HCl(4)O(4)(-), there are two perpendicular chains of hydrogen-bonded ions, one arising from the interaction between 2-carboxy-3,4,5,6-tetrachlorobenzoate ions and the other from the interaction between the 2-amino-6-methylpyridin-1-ium and 2-carboxy-3,4,5,6-tetrachlorobenzoate ions. These chains combine to form a two-dimensional network of hydrogen-bonded ions. Cocrystals of bis(2-amino-3-methylpyridin-1-ium) 3,4,5,6-tetrachlorophthalate-3,4,5,6-tetrachlorophthalic acid (1/1), 2C(6)H(9)N(2)(+)·C(8)Cl(4)O(4)(2-)·C(8)H(2)Cl(4)O(4), form finite aggregates of hydrogen-bonded ions. π-π interactions are observed between 2-amino-3-methylpyridin-1-ium cations. Both structures exhibit the characteristic R(2)(2)(8) motif as a result of the hydrogen bonding between the 2-aminopyridinium and carboxylate units.

Slave-boson mean-field study of the dimensional crossover in Sr2RuO4

The anomalous temperature dependence of the c-axis resistivity of Sr2RuO4 is analyzed under the viewpoint of a dimensional crossover which occurs from a lattice of perpendicular one-dimensional chains, belonging to different Ru-4d-orbitals, to a two-dimensional system induced by weak inter-orbital hybridization. This system is described by a two-orbital Hubbard model which is treated within a slave-boson mean-field approach to take correlation effects, such as the spin-charge separation, into account. We obtain the emergence of quasiparticle states at low temperature, a result which can be used to discuss the evolution of the spectral density and the c-axis transport within a tunneling approach. For the latter, a crossover between the low- and high-temperature regime is found in qualitative agreement with experimental observations.

Channels occupancy and distortion in new lithium uranyl phosphates with three-dimensional open-frameworks

Three new lithium uranyl phosphates, Li 2(UO 2) 3(PO 4) 2O ( 1), Li(UO 2) 4(PO 4) 3 ( 2) and Li 3(UO 2) 7(PO 4) 5O ( 3) were synthesized and studied. Powders of 1 and 2 were synthesized via solid state reaction, and single crystals of the three compounds were obtained by melting of 1 and 2 powders. The structures of the three compounds have been solved and refined from single crystal X-ray diffraction data. In the three compounds, the uranium atoms occupy square and pentagonal bipyramids. The uranium square bipyramids and phosphate tetrahedra are connected by vertices to form two types of layers with autunite sheet anion-topology ∞ 2 [ ( UO 2 ) ( PO 4 ) 2 ] 4 - and ∞ 2 [ ( UO 2 ) 2 ( PO 4 ) 3 ] 5 - denoted S and D, respectively. The uranyl pentagonal bipyramids share opposite equatorial edges to form ∞ 1 [ UO 5 ] 4 - infinite chains. Mutually perpendicular chains are hung on each side of the sheets to build frameworks with non-crossing perpendicular channels that accommodate the lithium ions. Various stacking sequences of the S and D layers, S–S, D–D and S–D, generate three different frameworks in 1, 2 and 3, respectively. These compounds are similar to the recently reported vanadate analogous. However, the phosphate tetrahedra, smaller than the vanadate ones, gives distortion of the layers and a lowering of the symmetry and/or a change of periodicity. The electrical conductivity of 1 and 2 was measured using impedance spectroscopy method. The rather low conductivity of the lithium cations is explained by the crystal structure and the Li + position within the tunnels. These results corroborate those on the analogous three-dimensional alkaline uranyl vanadates. Crystallographic data: 293 K, BRUKER X8-APEX2 X-ray diffractometer, 4 K CCD detector, Mo Kα, λ=0.71073 Å, full-matrix least-squares refinement on the basis of F. 1, Tetragonal symmetry, space group I4 1/ amd, Z=4 with a=7.1109(2) Å and c=25.0407(8) Å, R=0.034 and w R=0.047 for 38 parameters with 479 independent reflections with I⩾3 σ( I). 2, monoclinic symmetry, space group P2 1/ c, Z=4 and a=9.8829(2) Å, b=9.8909(2) Å, c=17.4871(4) Å and β=106.198(1)°, R=0.021 and w R=0.031 for 249 parameters with 4201 independent reflections with I⩾3 σ( I). 3, Tetragonal symmetry, space group P 4 ¯ 2 1 m with a=9.9305(2) Å and c=14.5741(3) Å, R=0.035 and w R=0.038 for 137 parameters with 4527 independent reflections with i⩾3 σ( I).

Tunable Soret‐Band Splitting of an Amphiphilic Porphyrin by Surface Pressure

Porphyrin aggregates, that is, Jand H-aggregates, have attracted much attention because of their peculiar structural and photophysical properties, which make them potential candidates for applications in nonlinear optics, nanometer-sized photoconductors, light-harvesting systems, and catalysis. Porphyrin aggregation can be detected through spectrum changes of the degenerated Soret band. For freebase porphyrins with D2h symmetry, the degeneracy is theoretically lost. However, the absorption is not detectably split and a sole increased bandwidth is apparent with respect to porphyrins with D4h symmetry. [2] Such splitting can be detected for densely packed porphyrins as a function of the molecular organization. Thus, the Soret band of freebase porphyrins can be described in terms of two mutually perpendicular oscillators (namely, Bx, By). Soret-band splitting of porphyrins has been described before. However, controlling this phenomenon is difficult because of the high tendency of porphyrins to autoaggregate. A tunable Soret-band splitting is described in this communication for the first time in the same experiment. A novel amphiphilic porphyrin, namely, (OD)3TPPS3 (see Figure 1)—with a selected balance between three meso-phenyl groups possessing hydrophilic sulfonato moieties and one meso-phenyl group bearing three long hydrophobic alkoxy chains—is synthesized. The used patterns are known to produce ordered array structures in porphyrins and fullerenes. Figure 1 shows the p–A isotherm of (OD)3TPPS3 as well as the ellipsotherm (dD–A isotherms) on the basic subphase (pH 11, NaOH). The monolayer stability is analyzed by means of area–time diagrams and compression–expansion cycles (see the Supporting Information). The analysis reveals the formation of a stable monomolecular layer of (OD)3TPPS3 at the air–water interface. Moreover, from the ellipsometric study (see the Supporting Information), we calculate a thickness of 3.17 nm (A= 0.9 nm), which corresponds to a monolayer of upright porphyrins with perpendicular alkyl chains at the air–water interface for such a full-packing phase. Reflection spectroscopy of monolayers can selectively detect molecules at the air–water interface because of the reflectionenhanced effect that originates from absorption. Figure 2 shows reflection spectra (DR) of monolayers of (OD)3TPPS3 on Figure 1. Molecular structure of 5,10,15-tris(4-sulfonatophenyl)-20-(3,4,5-trin-octadecyloxyphenyl)porphyrin (OD)3TPPS3. p–A isotherm (c) and ellipsotherm, dD–A (g) of a monolayer of (OD)3TPPS3 at the air–water interface with basic subphase (pH 11, NaOH).

Spin Gap and String Order Parameter in the Ferromagnetic Spiral Staircase Heisenberg Ladder: A Quantum Monte Carlo Study

We consider a spin-1/2 ladder with a ferromagnetic rung coupling J perpendicular and inequivalent chains. This model is obtained by a twist (theta) deformation of the ladder and interpolates between the isotropic ladder (theta=0) and the SU(2) ferromagnetic Kondo necklace model (theta = pi). We show that the ground state in the (theta, J perpendicular) plane has a finite string order parameter characterizing the Haldane phase. Twisting the chain introduces a new energy scale, which we interpret in terms of a Suhl-Nakamura interaction. As a consequence we observe a crossover in the scaling of the spin gap at weak coupling from delta/J parallel proportional, variant J perpendicular/J parallel for theta < theta c approximately 8 pi/9 to delta/J parallel proportional, variant (J perpendicular/J parallel)2 for theta > theta c. Those results are obtained on the basis of large scale quantum Monte Carlo calculations.

LiFe(MoO4)2, LiGa(MoO4)2and Li3Ga(MoO4)3

The structures of lithium iron dimolybdate, LiFe(MoO4)2, and lithium gallium dimolybdate, LiGa(MoO4)2, are shown to be isomorphous with each other. Their structures consist of segregated layers of LiO6 bicapped trigonal bipyramids and Fe(Ga)O6 octahedra separated and linked by layers of isolated MoO4 tetrahedra. The redetermined structure of trilithium gallium trimolybdate, Li3Ga(MoO4)3, shows substitional disorder on the Li/Ga site and consists of perpendicular chains of LiO6 trigonal prisms and two types of differently linked Li/GaO6 octahedra.

Crystal structure and local order in Co6Al11−x Si6+x

The ternary compound Co(6)Al(11-x)Si(6+x) (epsilon phase) was prepared from the elements by arc melting and subsequent heat treatment, and then characterized by single-crystal X-ray diffraction (XRD), electron-probe microanalysis (EPMA), differential thermal analysis (DTA) and transmission electron microscopy (TEM). This new structure type consists of planar layers with the composition [Co(6)Al(10)Si(4)], which are penetrated by perpendicular (Si-Si-Al) chains. While the layers are well described by an orthorhombic model (space group Pnma, Pearson symbol oP46), the chains exhibit doubled periodicity, thus yielding a superstructure. Two alternative ordering models (space group Cmc2(1), oC184, and space group P2(1)/c, mP92) are presented and discussed based on XRD and TEM results. The (Si-Si-Al) chains are located in pentagonal antiprismatic ;channels' which reveal the similarity of the Co(6)Al(11-x)Si(6+x) structure to Al-rich transition-metal compounds such as Co(4)Al(13), Co(2)Al(5), Fe(4)Al(13), V(7)Al(45), V(4)Al(23) and VAl(10), which also exhibit this type of pentagonal ;channels' in their crystal structures. The phase shows only a very small homogeneity range.

Three-dimensional framework of uranium-centered polyhedra with non-intersecting channels in the uranyl oxy-vanadates A2(UO 2) 3(VO 4) 2O ( A=Li, Na)

The uranyl vanadates A 2(UO 2) 3(VO 4) 2O ( A=Li, Na) have been synthesized by solid-state reaction and the structure of the Li compound was solved from single-crystal X-ray diffraction. The crystal structure is built from ∞ 1 [ UO 5 ] 4 - chains of edge-shared U(2)O 7 pentagonal bipyramids alternatively parallel to a ⇒ - and b ⇒ -axis and further connected together to form a three-dimensional (3-D) arrangement. The perpendicular chains are hung on both sides of a sheet ∞ 2 [ ( UO 2 ) ( VO 4 ) 2 ] 4 - parallel to (001), formed by U(1)O 6 square bipyramids connected by VO 4 tetrahedra, and derived from the autunite-type sheet. The resulting 3-D framework creates non-intersecting channels running down the a ⇒ - and b ⇒ -axis formed by empty face-shared oxygen octahedra, the Li + ions are displaced from the center of the channels and occupy the middle of one edge of the common face. The peculiar position of the Li + ion together with the full occupancy explain the low conductivity of Li 2(UO 2) 3(VO 4) 2O compared with that of Na(UO 2) 4(VO 4) 3 containing the same type of channels half occupied by Na + ions in the octahedral sites. Crystallographic data for Li 2(UO 2) 3(VO 4) 2O: tetragonal, space group I41/ amd, a = 7.3303 ( 5 ) Å , c = 24.653 ( 3 ) Å , V = 1324.7 ( 2 ) Å 3 , Z = 4 , ρ mes=5.32(2) g/cm 3, ρ cal=5.36(3) g/cm 3, full-matrix least-squares refinement basis on F 2 yielded, R 1 = 0.032 , w R 2 = 0.085 for 37 refined parameters with 364 independent reflections with I ⩾ 2 σ ( I ) .

Disproportionation of Pyrazine in NH+···N Hydrogen-Bonded Complexes: New Materials of Exceptional Dielectric Response

Centrosymmetric pyrazinium NH+...N bonded complexes allow their dielectric properties to be analyzed separately from the bulk ferroelectric polarization observed in the noncentrosymmetric DABCO monosalts. The method of dielectric permittivity measurements has been employed for monitoring polarization fluctuations generated by proton transfers in the NH+...N bonded linear polycations. The revealed dielectric response of [C4H5N2]+BF4- and [C4H5N2]+ClO4- cannot be reconciled with the centrosymmetric symmetry of their structures, but suggests formation of polar defects or nanoregions. Unique transformations of the pyrazine [C4H5N2]+BF4- complex between linear NH+...N hydrogen-bonded polycationic aggregates antiparallel in phase gamma, perpendicular chains in phase beta, and with NH+...N bonds broken in phase alpha have been observed. The [C4H5N2]+ClO4- and [C4H5N2]+BF4- complexes as grown at 290 K are isostructural in orthorhombic phase , space group Pbcm, with linear polycationic chains arranged antiparallel. On heating, the tetrafluoroborate and perchlorate salts each undergoes two first-order phase transitions at similar temperatures about 340-360 K, while on cooling only one phase transition has been observed. An extremely unique sequence of two phase transitions subsequently lowering the symmetry of the [C4H5N2]+BF4- crystal when temperature is increased has been evidenced: the orthorhombic phase heated above 343 K transforms into the monoclinic C2/c-symmetric phase beta, in which the NH+...N bonded linear chains assume perpendicular arrangement; and at about 353-357 K the anions and cations adopt a typical ionic-crystal packing without homonuclear NH+...N hydrogen bonds in a still lower-symmetry monoclinic P21/n-symmetric structure. The exceptional perpendicular arrangement of the linear NH+...N bonded chains in phase beta constitutes a unique system where polarization of small regions can assume various orientations within a plane, depending on the H+ sites. No phase transitions or anomalous dielectric response were observed in the NH+...O bonded [C4H5N2]+NO3- complex. The unprecedented structure-property relations of the pyrazinium complexes fully confirm the role of the NH+...N bond transformations for the dielectric response of analogous DABCO ferroelectrics.

The crystal structure of methanol monohydrate (CD 3OD · D 2O) at 160 K from powder neutron diffraction

The structure of methanol monohydrate at 160 K has been solved from powder neutron diffraction data by ab initio methods. The crystal is orthorhombic, space-group Cmc2 1 ( Z = 4) with unit cell dimensions a = 4.64910(2) Å, b = 14.08464(7) Å, c = 4.69358(1) Å, V = 307.340(2) Å 3 ( ρ calc = 1212.29(1) kg m −3) at 160 K. The structure consists of water–water chains, linked by ordered hydrogen bonds extending along the c-axis, which cross link methanol–water chains with disordered hydrogen bonds along the a-axis. These perpendicular chains form sheets which are stacked parallel to the b-axis.

A novel Cd complex with 3D framework containing perpendicular chains and helices

The hydrothermal reaction of CdBr 2 · 2H 2O with a flexible multicarboxylate ligand, trans-aconitic acid (H 3L), produced a novel coordination compound [Cd 3L 2(H 2O) 6] n . It crystallizes in the space group C2/c with a = 17.1304(1) Å, b = 9.5611(2) Å, c = 14.0137(2) Å, β = 115.96°, Z = 4, V = 2063.65(5) Å 3. The unique feature of the structure is an unprecedented 3D framework containing infinite Cd(1)–O–C linear chains and heterochiral Cd(2)–O–C single-stranded helices. These linear chains and helices happen to be perpendicular to each other.

Magnetization reversal in cobalt antidot arrays

We have carried out a detailed study of the magnetic switching in square lattice cobalt antidot arrays with periods ranging from $2\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ down to $200\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ (antidot $\text{size}=\text{antidot}$ separation). Magneto-optical Kerr effect measurements show first a small change in the magnetization due to a reversible rotation of the magnetic spins in the antidot rows, followed by a large change due to reversal of the antidot array columns parallel to the applied field. Employing x-ray photoemission electron microscopy and transmission x-ray microscopy, the latter irreversible process was observed as a nucleation and propagation of discrete domain chains. The propagating chain ends are blocked by perpendicular chains present in the antidot rows via various mechanisms revealed by micromagnetic simulations.

Theoretical studies of plasmon resonances in one-dimensional nanoparticle chains: narrowlineshapes with tunable widths

In this paper we describe a new configuration for producing narrow extinction lineshapesfor light scattering from one-dimensional arrays of silver nanoparticles. In thisconfiguration, which is specifically concerned with an array with a finite number ofrelatively large (radius greater than around 30 nm) nanoparticles, the wavevector of thelight is chosen to be parallel to the array axis, while the polarization direction isperpendicular to the array axis. This leads to narrow plasmon/photonic lineshapes whenthe particle spacing is half the incident wavelength. This effect stands in contrast to thenarrow lines previously found for wavevector and polarization vector perpendicular to thearray axis, where the optimum spacing is close to the wavelength. The results arerationalized using a semi-analytical evaluation of the coupled dipole interaction, and it isdemonstrated that the parallel and perpendicular chains have very different dependence onthe number of particles in the chain. Results as a function of chain orientation relativeto the wavevector are also considered, as is the possibility of sensing using anarray configuration that combines the parallel and perpendicular chain directions.

Neutron scattering studies of the spin icesHo2Ti2O7andDy2Ti2O7in applied magnetic field

Neutron diffraction has been used to investigate the magnetic correlations in single crystals of the spin ice materials Ho2Ti2O7 and Dy2Ti2O7 in an external magnetic field applied along either the [001] or [1-10] crystallographic directions. With the field applied along [001] a long range ordered groundstate is selected from the spin ice manifold. With the field applied along [1-10] the experiments show that the spin system is separated into parallel (alpha) and perpendicular (beta) chains with respect to the field. This leads to partial ordering and the appearance of quasi-one-dimensional magnetic structures. In both field orientations this frustrated spin system is defined by the appearance of metastable states, magnetization plateaux and unusually slow, field regulated dynamics.