Evidence for polarized nanoregions from the domain dynamics in multiferroic LiCuVO4.

LiCuVO4 is a model system of a 1D spin-1/2 chain that enters a planar spin-spiral ground state below its Néel temperature of 2.4 K due to competing nearest and next nearest neighbor interactions. The spin-spiral state is multiferroic with an electric polarization along the a axis which has been proposed to be caused purely by the spin supercurrent mechanism. With external magnetic fields in c direction TN can be suppressed down to 0 K at 7.4 T. Here we report dynamical measurements of the polarization from P(E)-hysteresis loops, magnetic field dependent pyro-current and non-linear dielectric spectroscopy as well as thermal expansion and magnetostriction measurements at very low temperatures. The multiferroic transition is accompanied by strong anomalies in the thermal expansion and magnetostriction coefficients and we find slow switching times of electric domain reversal. Both observations suggest a sizable magnetoelastic coupling in LiCuVO4. By analyzing the non-linear polarization dynamics we derive domain sizes in the nm range that are probably caused by Li defects.

Structural and magnetic phase transitions in Cs2[FeCl5(H2O)].

The compound [Formula: see text] is magnetoelectric but not multiferroic with an erythrosiderite-related structure. We present a comprehensive investigation of its structural and antiferromagnetic phase transitions by polarization microscopy, pyroelectric measurements, x-ray diffraction and neutron diffraction. At about [Formula: see text] K, the compound changes its symmetry from Cmcm to I2/c, with a doubling of the original c-axis. This transformation is associated with rotations of the [Formula: see text] octahedra and corresponds to an ordering of the [Formula: see text] molecules and of the related [Formula: see text] bonds. A significant ferroelectric polarization can be excluded for this transition by precise pyrocurrent measurements. The antiferromagnetic phase transition occurring at [Formula: see text] results in the magnetic space group [Formula: see text], which perfectly agrees with previous measurements of the linear magnetoelectric effect and magnetization.

Sellmeier equations, group velocity dispersion, and thermo-optic dispersion formulas for CaLnAlO4 (Ln = Y, Gd) laser host crystals.

We studied the refractive index and dispersive properties of the tetragonal rare-earth calcium aluminates, CaLnAlO4 (Ln=Gd or Y). Sellmeier equations were derived for the spectral range of 0.35-2.1 µm. The group velocity dispersion (GVD) in CaGdAlO4 is positive at ∼1 µm, 95 fs2/mm and negative at ∼2 µm, -40 fs2/mm. The GVD values for CaYAlO4 are similar. In addition, thermo-optic coefficients, dn/dT, and thermal coefficients of the optical path were determined for CaYAlO4. dn/dT is negative at ∼1 µm, dno/dT=-7.8, and dne/dT=-8.7×10-6 K-1. Thermo-optic dispersion formulas were constructed. The obtained data are of key importance to the design of high-power mode-locked oscillators at ∼1 and ∼2 µm based on such laser hosts.

Magnetically driven second-harmonic generation with phase matching in MnWO4.

Phase matching is known to enhance the nonlinear optical response in materials with a non-centrosymmetric crystallographic or electronic structure. In contrast, phase-matched frequency doubling driven by non-centrosymmetric magnetism that induces acentricity in otherwise centrosymmetric structures has not been reported yet. In our study we demonstrate the emergence of magnetically driven second-harmonic generation (SHG) with phase matching in MnWO4. The phase-matched wavelength for SHG can be tuned continuously between 450 nm to 630 nm with the conversion efficiency being determined by the refractive indices and their dispersion. Our findings reveal a new strategy towards magnetism-based conversion-materials and a route for controlling the nonlinear signal yield by acting primarily on the material's spin degree of freedom rather than employing its electronic or structural properties.

Second-harmonic generation of light at 245 nm in a lithium tetraborate whispering gallery resonator.

A millimeter-sized, monolithic whispering gallery resonator made of a lithium tetraborate, Li2B4O7, crystal was employed for doubly resonant second-harmonic generation with a continuous-wave laser source at 490 nm. An intrinsic quality factor of 2×10(8) was observed at the pump wavelength. A conversion efficiency of 2.2% was attained with 5.9 mW of mode-matched pump power. In the lithium tetraborate resonator, it is feasible to achieve phase-matching of second-harmonic generation for pump wavelengths between 486 and 506 nm.

Neodymium(III) molybdenum(VI) borate, NdBO(2)MoO(4).

Single crystals of NdBO(2)MoO(4) were obtained from a molybdenum oxide-boron oxide flux under an air atmosphere. The structure features double chains of edge- and face-sharing distorted [NdO(10)] bicapped square-anti-prisms, which are linked by rows of isolated [MoO(4)] tetra-hedra and by zigzag chains of corner-sharing [BO(3)] groups, all of them running along the b axis. The chains of [NdO(10)], chains of [BO(3)] and rows of [MoO(4)] groups are arranged in layers parallel to the bc plane.

catena-Poly[[manganese(II)-tris-(µ-bet-aine-κO:O')] tetra-bromido-manganate(IV).

The title compound, [Mn(C(5)H(11)NO(2))(3)]·MnBr(4), contains polymeric cationic chains of distorted MnO(6) octa-hedra and bridging betaine mol-ecules, running parallel to the a axis. There are two distinct Mn(2+) cations in the chain, both with site symmetry . Distorted [MnBr(4)](2-) tetra-hedra occupy the spaces between the chains.

Compounds of glycine with metal sulfates and thiosulfates: glycine cobalt sulfate pentahydrate, glycine sodium thiosulfate dihydrate and glycine potassium thiosulfate.

In the crystal structures of the title compounds, hexaaquacobalt(II) tetraaquadiglycinatocobalt(II) bis(sulfate), [Co(H2O)6][Co(C2H5NO2)2(H2O)4](SO4)2, (I), poly[diaqua-mu3-glycinato-di-mu4-thiosulfato-tetrasodium(I)], [Na4(C2H5NO2)(S2O3)2(H2O)2]n, (II), and poly[mu2-glycinato-mu4-thiosulfato-dipotassium(I)], [K2(C2H5NO2)(S2O3)]n, (III), all atoms are located on general positions, except the Co atoms in (I), which are located on inversion centres. In (I), hydrogen bonds play an important role, while the alkali thiosulfate compounds are characterized by three-dimensional frameworks of polyhedra. Relations to other compounds of glycine and metal sulfates are commented on.

Two novel glycine metal halogenides: catena-poly[[[diaquanickel(II)]-di-mu-glycine] dibromide] and catena-poly[[[tetraaquamagnesium(II)]-mu-glycine] dichloride].

In catena-poly[[[diaquanickel(II)]-di-mu-glycine] dibromide], {[Ni(C2H5NO2)2(H2O)2]Br2}n, (I), the Ni atom is located on an inversion centre. In catena-poly[[[tetraaquamagnesium(II)]-mu-glycine] dichloride], {[Mg(C2H5NO2)(H2O)4]Cl2}n, (II), the Mg atom and the non-H atoms of the glycine molecule are located on a mirror plane. All other atoms are located on general positions. The atomic arrangements of both compounds are characterized by [MO6] octahedra (M=Ni or Mg) connected by glycine molecules, with the halogenide ions in the interstices. In (I), four of the coordinating O atoms are from glycine and two are from water molecules, building layers of octahedra and organic molecules. In (II), two of the coordinating O atoms are from glycine and four are from water molecules. The octahedra and organic molecules form chains.

Three novel non-centrosymmetric compounds of glycine: glycine lithium sulfate, glycine nickel dichloride dihydrate and glycine zinc sulfate trihydrate.

The crystal structures of three compounds of glycine and inorganic materials are presented and discussed. The orthorhombic structure of glycinesulfatodilithium(I), [Li(2)(SO(4))(C(2)H(5)NO(2))](n), consists of corrugated sheets of [LiO(4)] and [SO(4)] tetrahedra. The glycine molecules are located between these sheets. The main features of the monoclinic structure of diaquadichloroglycinenickel(II), [NiCl(2)(C(2)H(5)NO(2))(H(2)O)(2)](n), are helical chains of [NiO(4)Cl(2)] octahedra connected by glycine molecules. The orthorhombic structure of triaquaglycinesulfatozinc(II), [Zn(SO(4))(C(2)H(5)NO(2))(H(2)O)(3)](n), is made up of [O(3)SOZnO(5)] clusters. These clusters are linked by glycine molecules into zigzag chains. All three compounds are examples of non-centrosymmetric glycine compounds.