Temperature‐dependent Raman scattering study of multiferroic MnWO4

We have measured polarized Raman spectra of MnWO₄ single crystals at low temperatures, and studied the temperature dependence of the various phonon modes. From our Raman studies of the MnWO₄, a new transition temperature, ∼180 K, was found. We have completely assigned the symmetries of the 18 observed Raman modes of the MnWO₄, as expected from a group theoretical analysis. These Raman modes have been classified into three groups according to weak, intermediate and strong temperature dependence of the modes in each group. Six internal modes have been identified by their weak temperature dependence of the Raman wavenumbers. The temperature dependence of the wavenumbers of the B_g modes in Mg O bonds, modes of intermediate temperature dependence group, shows an anomalous behavior under 50 K. The phonon modes of strong temperature dependence show an anomalous change at ∼180 K in the linewidths. This is believed to be a new transition temperature which involves the changes in the inter‐WO₆ octahedra structure. Copyright © 2009 John Wiley & Sons, Ltd.     

A compact optical heterodyne interferometer by optical integration and its application

A compact high-resolution optical heterodyne interferometer combining a two-frequency light module and a minute optical system is described. The light module, which generates two independent frequencies of light, is fabricated by proton exchange method on LiNbO₃ substrate. We report an experiment evaluating measurement accuracy using a micro-displacement measurement system which incorporates this interferometer. Results of the experiment with a standard thickness sample show high thermal stability with maximum measurement error of 1.8 nm at a temperature from 19°C to 33°C. The system was used to measure the hysteresis of a piezoelectric element for displacements of several nm, thereby making it possible to analyze the system quantitatively in practice.     

Direct observation of chiral susceptibility in the canonical spin glass AuFe

The extraordinary Hall resistivity rho(xy) and the magnetization M of a canonical spin glass AuFe (8 at.% Fe) were measured simultaneously as functions of temperature with the best care to the thermal and the magnetic field hysteresis. The data of rho(xy) show an anomaly at the spin glass transition temperature T(g) and have different zero field cooling (ZFC) and field cooling (FC) measurements below T(g). Moreover, the value of rho(xy)/M, which represents the chiral susceptibility of the system in the present case, also shows the difference between ZFC and FC measurements. The results are consistent with the predictions of the chirality scenario of canonical spin glasses by Kawamura.     

Nature of the well screened state in hard X-ray Mn 2p core-level photoemission measurements of La1-xSrxMnO3 films

Using hard x-ray (HX; hnu=5.95 keV) synchrotron photoemission spectroscopy (PES), we study the intrinsic electronic structure of La(1-x)Sr(x)MnO(3) (LSMO) thin films. Comparison of Mn 2p core-levels with soft x-ray (SX; hnu approximately 1000 eV) PES shows a clear additional well-screened feature only in HX PES. Takeoff-angle dependent data indicate its bulk (> or =20 A) character. The doping and temperature dependence track the ferromagnetism and metallicity of the LSMO series. Cluster model calculations including charge transfer from doping-induced states show good agreement, confirming this picture of bulk properties reflected in Mn 2p core-levels using HX PES.     

Preparation of Cu2ZnSnS4 thin films by hybrid sputtering

In order to fabricate Cu₂ZnSnS₄ thin films, hybrid sputtering system with two sputter sources and two effusion cells is used. The Cu₂ZnSnS₄ films are fabricated by the sequential deposition of metal elements and annealing in S flux, varying the substrate temperature. The Cu₂ZnSnS₄ films with stoichiometric composition are obtained at the substrate temperature up to 400 °C, whereas the film composition becomes quite Zn-pool at the substrate temperature above 450 °C. The Cu₂ZnSnS₄ film shows p-type conductivity, and the optical absorption coefficient and the band gap of the Cu₂ZnSnS₄ film prepared in this experiment are suitable for fabricating a thin film solar cell.     

High-energy scale revival and giant kink in the dispersion of a cuprate superconductor

In the present photoemission study of a cuprate superconductor Bi1.74Pb0.38Sr1.88CuO6+delta, we discovered a large scale dispersion of the lowest band, which unexpectedly follows the band structure calculation very well. Similar behavior observed in blue bronze and the Mott insulator Ca2CuO2Cl2 suggests that the origin of hopping-dominated dispersion in an overdoped cuprate might be quite complicated. A giant kink in the dispersion is observed, and the complete self-energy containing all interaction information is extracted for a doped cuprate. These results recovered significant missing pieces in our current understanding of the electronic structure of cuprates.     

Qβ measurements of 158, 159Pm , 159, 161Sm , 160-165Eu , 163Gd and 166Tb using a total absorption BGO detector

Q _β values of the neutron-rich isotopes of ^160-165Eu and ¹⁶³Gd were measured for the first time using a total absorption bismuth germanate (BGO) detector, and previously obtained data on ^{158, 159}Pm , ^{159, 161}Sm and ¹⁶⁶Tb were re-analyzed. These radioactive sources were prepared by an on-line mass separator (Tokai-ISOL) following the ²³⁸U (p,f reaction. The deduced Q _β values are the following: 6085(80)keV for ¹⁵⁸Pm , 3805(65)keV for ¹⁵⁹Sm , 5460(140)keV for ¹⁵⁹Pm , 4705(60)keV for ¹⁶⁰Eu , 5065(130)keV for ¹⁶¹Sm , 3705(60)keV for ¹⁶¹Eu , 5575(60)keV for ¹⁶²Eu , 4690(70)keV for ¹⁶³Eu , 3170(70)keV for ¹⁶³Gd , 6430(70)keV for ¹⁶⁴Eu , 5800(120)keV for ¹⁶⁵Eu , and 4695(70)keV for ¹⁶⁶Tb . Moreover, the deduced mass excesses and two-neutron separation energies ( S _2n values) were compared with those of the atomic mass evaluations and theoretical predictions.     

Fast‐response organic–inorganic hybrid light‐emitting diode

We demonstrated important changes produced on the modulation frequency of hybrid organic–inorganic light‐emitting diodes to examine the applicability as a light source for visible optical communications. The fabricated device structure was 4,4′‐bis[N ‐(1‐napthyl)‐N ‐phenyl‐amino]biphenyl/4,4′‐(bis(9‐ethyl‐3‐carbazovinylene)‐1,1′‐biphenyl:4,4′‐bis[9‐dicarbazolyl]‐2,2′‐biphenyl/ZnS/LiF/MgAg. This device showed an improvement in the modulation frequency using ZnS instead of an organic material, tris(8‐hydroxyquinoline)aluminum. A maximum cutoff frequency of 20.6 MHz was achieved.

     

ac ionic conductivity of hollandite type compounds from 100 Hz to 37.0 GHz

The frequency- and temperature-dependences of a.c. ionic conductivity of one-dimensional super-ionic conductors K-priderites with a hollandite type structures were investigated from 100 Hz to 37.0 GHz. Four kinds of K-priderite, K_1.6Mg_0.8Ti_7.2O₁₆, (K_1.3, Li_0.1) Mg_0.7Ti_7.3O₁₆, K_1.6Al_1.6Ti_6.4O₁₆ and (K_1.3, Li_0.2) Al_1.5Ti_6.5O₁₆, were studied. An equivalent circuit to combine the data of the complex conductivity at low and high frequencies was proposed. The data of complex conductivity at low frequencies can be analyzed in terms of the moving box model proposed by Beyeler et al. The transport of K⁺ ions at low frequencies is characterized by the cooperative motion of the K⁺ ions with various mobilities and is accompanied with the polarization of the K⁺ ions in the channels. The ion transport across intrinsic barriers at or above microwave frequencies is characterized by the frequency-independent ionic conductivity and is interpreted by the configurational model proposed by Beyeler et al. The height of intrinsic barriers is related to the lattice constants of a crystal.     

Three-body calculation of neutron-deuteron elastic scattering in the energy region from 2.5 MeV up to 50 MeV

The three-body Faddeev equations for neutron-deuteron scattering are solved in the energy region from 2.5 MeV to 50 MeV of the incident neutron energy with small energy steps. Higher-rank separable potentials are used in the¹ s ₀ wave and in the³ s ₁—³ d ₁ waves, while rank-1 separable potentials are used in¹ p ₁,³ p _0,1,2 ¹ d ₂ ³ d _2,3 waves. The calculation is compared with experiments for the total cross section, the total break-up cross section, the differential cross section and the analyzing power of neutron-deuteron scattering. The improvements in the agreement as compared to previous calculations are impressive in many cases. Especially, the calculated total cross section agrees with the experiment below 30 MeV within the error bars, which are as small as 1%. A discussion on the numerical accuracy is given. General aspects of the calculated cross section are discussed. It is pointed out that thes-wave asymptotic normalization of the deuteron wave function (A _s ) is important.