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The compounds A(2)[FeCl5(H2O)] with A = K, Rb, Cs are identified as new linear magnetoelectric (non-multiferroic) materials. We present a detailed investigation of their linear magnetoelectric properties through measurements of pyroelectric currents, dielectric constants and magnetization. The anisotropy of the linear magnetoelectric effect of the K-based and Rb-based compound is consistent with the magnetic point group m' m' m' , already reported in literature. A symmetry analysis of the magnetoelectric effect of the Cs-based compound allows us to determine the magnetic point group mmm' and to develop a model for its magnetic structure. In addition, magnetic-field versus temperature phase diagrams are derived and compared to the closely related multiferroic (NH4)(2)[FeCl5(H2O)].

We report on polarized infrared reflectivity measurements of multiferroic, monoclinic MnWO4 between 10 and 295 K. All five nonvanishing components of the dielectric tensor have been determined in the frequency range of the phonons. All infrared-active phonon modes (7 A(u) modes and 8 B-u modes) are unambiguously identified. In particular, the strongest B-u modes have been overlooked in previous studies, in which the monoclinic symmetry was neglected in the analysis. The combined analysis of reflectance data measured in different experimental geometries (R-ac and R-p) is particularly helpful for a proper identification of the B-u modes. Using a generalized Drude-Lorentz model, we determine the temperature dependence of the phonon parameters, including the orientation of the B-u modes within the ac plane. The phonon parameters and their temperature dependence were discussed controversially in previous studies, which did not include a full polarization analysis. Our data do not confirm any of the anomalies reported above 20 K. However, in the paramagnetic phase we find a drastic reduction of the spectral weights of the weakest A(u) mode and of the weakest B-u mode with increasing temperature. Below 20 K, the parameters of the A(u) phonon modes for E vertical bar vertical bar b show only subtle changes, which demonstrate a finite but weak coupling between lattice dynamics and magnetism in MnWO4. A quantitative comparison of our infrared data with the quasistatic dielectric constant epsilon(b) yields a rough estimate for the oscillator strength Delta epsilon(em) less than or similar to 0.02 of a possible electromagnon for E vertical bar vertical bar b. Furthermore, we report on a Kramers-Kronig-consistent model which is able to describe non-Lorentzian line shapes in compounds with monoclinic symmetry.

Monoclinic non-centrosymmetric guanylurea(1+) hydrogen phosphite (GUHP), (NH2)(2)CNHCO(NH2)H2PO3, was found to be an attractive SRS-active crystal manifesting numerous ((3))- and ((2))-nonlinear optical interactions. In particular, with picosecond single- and dual-wavelength pumping SHG, THG (via cascaded parametric four-wave processes), high-order Stokes and anti-Stokes lasing related to the ten SRS-active phonon modes of the crystal, octave spanning ((3))-lasing combs and cross-cascaded ((3)(3)) effects with different pairs of SRS-phonons were observed. The comparative estimation of the first Stokes steady-state Raman gain coefficients in the near-IR region allows the tentative conclusion, that their values can satisfy the practical requirements for the development of Raman laser converters. All recorded Raman-induced lasing lines were identified and attributed to the ((3))-active vibration modes of the crystal. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Comparing high-resolution specific heat and thermal expansion measurements to exact finite-size diagonalization, we demonstrate that Cs2CoCl4 for a magnetic field along the crystallographic b axis realizes the spin-1/2 XXZ chain in a transverse field. Exploiting both thermal as well as virtual excitations of higher crystal-field states, we find that the spin chain is in the XY limit with an anisotropy J(z)/J(perpendicular to) approximate to 0.12, substantially smaller than previously believed. A spin-flop Ising quantum phase transition occurs at a critical field of mu H-0(b)cr approximate to 2 T before around 3.5 T the description in terms of an effective spin-1/2 chain becomes inapplicable.

We show that the electric-field-induced reversal of the magnetic order parameter in multiferroic MnWO4 occurs on the time scale of milliseconds. Throughout the switching process the magnetic order and the magnetically induced electric polarization remain rigidly coupled. The temporal progression of the domain structure was imaged with nanosecond resolution by an electrical-pump-optical-probe technique using optical second harmonic generation. The nonequilibrium domain pattern significantly differs from the one during quasistatic domain reversal. A qualitative model gives an estimate of why the magnetoelectric order-parameter reversal in the magnetically induced ferroelectrics is not inherently ultrafast.

Orthorhombic crystals of SrSO4, BaSO4, and PbSO4, known as natural crystals celestine, barite, and anglesite, were found to be attractive chi ((3))-active nonlinear optical materials. High-order Stokes and anti-Stokes picosecond generation that spans almost two octaves has been recorded with single-wavelength laser excitation in the UV, visible, and near-IR ranges. All recorded Raman induced lasing components were identified and attributed to the SRS-promoting vibration modes of the studied crystals (omega (SRS)a parts per thousand 999 cm(-1) for SrSO4,omega (SRS)a parts per thousand 985 cm(-1) for BaSO4 and omega (SRS)a parts per thousand 977 cm(-1) for PbSO4). Under dual-wavelength (lambda (f1)=1.06415 mu m + lambda (f2)=0.53207 mu m) collinear coherent picosecond pumping several new manifestations of cascaded chi ((3)) <-> chi ((3)) nonlinear up-conversion lasing effects were observed in BaSO4 and SrSO4 crystals. We classify all three studied sulfate crystals as promising SRS-active materials for Raman laser frequency converters and as efficient chi ((3))-crystals that efficiently generate Stokes and anti-Stokes frequency combs, which can enable experiments of ultra-short pulse syntheses.

Different nonlinear optical interactions in a novel SRS-active non-centrosymmetric tetragonal crystal Ca2ZnSi2O7 were investigated at room and cryogenic (9 K) temperature under picosecond laser pumping. In addition to measuring octave-spanning Stokes and anti-Stokes combs we observed several cascaded and cross-cascaded ?(3) ? ?(3) effects involving several SRS-active phonons. All recorded Raman-induced lasing lines in the visible and near-IR range are identified and attributed to the SRS-promoting vibration transitions. A brief review of SRS- and Nd3+-doped laser-active melilite-type crystals is given as well. ((c) 2011 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) ((c) 2011 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA)

Efficient room-temperature Stokes and anti-Stokes chi((3))-nonlinear picosecond generation, which spans more than two octaves (approximate to 23012 cm(-1)) has been observed in a natural crystal of orthorhombic SrSO4 (celestine). All recorded lasing lines in the visible and near-IR regions are identified and attributed to its SRS-promoting vibration mode omega(SRS) approximate to 999 cm(-1). [GRAPHICS] (C) 2010 by Astro Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA

Non-centrosymmetric tetragonal crystal Ca2MgSi2O7:Nd3+(Na+) with incommensurately modulated melilite-type structure is presented as a new laser crystal. By LD and Xe-flashlamp pumping its CW and free-running pulsed stimulated emission of the F-4(3/2) -> I-4(11/2) generation channel of Nd3+ lasant ions was excited. [GRAPHICS] The single exponential decay-time plot of the metastable F-4(3/2) (initial laser) state of Nd3+ ions in a Ca2MgSi2O7 crystal together with approximate to 10 mu s excitation pulses (C) 2010 by Astro Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA