Search For Spin-lattice Coupling Mediated By Itinerant Electrons: Synchrotron X-ray Diffraction And Raman Scattering From Gd Al3

The coupling among the spin degree of freedom and the atomic displacements in intermetallic Gd Al3 was investigated by means of synchrotron x-ray diffraction and polarized Raman scattering. In this compound, the Gd 4 f7 shell is spherical and the spin-lattice coupling provides a fingerprint of the exchange mechanism and degree of magnetic correlations. X-ray diffraction shows nonresonant symmetry-forbidden charge Bragg peaks below the long-range magnetic ordering temperature TN =18 K, revealing a symmetry-lowering crystal lattice transition associated with Gd displacements, consistent with a Ruderman-Kittel-Kasuya-Yosida mechanism for the magnetic coupling. Raman scattering in fresh broken surfaces shows phonons with conventional frequency behavior, while naturally grown and polished surfaces present frequency anomalies below T* ∼50 K. Such anomalies are possibly due to a modulation of the magnetic energy by the lattice vibrations in a strongly spin-correlated paramagnetic phase. Such interpretation implies that the spin-phonon coupling in metals may depend on the surface conditions. A fully spin-correlated state immediately above TN is inferred from our results in this frustrated system. © 2008 The American Physical Society.772(1999) Physics of Manganites, , edited by T. A. Kaplan and S. D. Mahanti (Springer, New YorkCheong, S.-W., Mostovoy, M., (2007) Nat. Mater., 6, p. 13. , See, for example, NMAACR 1476-1122 10.1038/nmat1804De Campos, A., Rocco, D.L., Carvalho, A.M.G., Caron, L., Coelho, A.A., Gama, S., Da Silva, L.M., De Oliveira, N.A., (2006) Nat. Mater., 5, p. 802. , NMAACR 1476-1122 10.1038/nmat1732Azimonte, C., Cezar, J.C., Granado, E., Huang, Q., Lynn, J.W., Campoy, J.C.P., Gopalakrishnan, J., Ramesha, K., (2007) Phys. Rev. Lett., 98, p. 017204. , PRLTAO 0031-9007 10.1103/PhysRevLett.98.017204Baltensperger, W., Helman, J.S., (1968) Helv. Phys. 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Magnetically Frustrated Behavior In Multiferroics R Mn2 O 5 (r=bi, Eu, And Dy): A Raman Scattering Study

A temperature dependent Raman scattering study in multiferroic single crystals R Mn2 O5 (R=Bi, Eu, and Dy) was performed. The Raman spectra were measured in the range from 150 to 450 cm-1 involving mostly Mn-O-Mn bending vibrations, complementing our previous work in a higher frequency range involving Mn-O stretching modes. A number of studied phonons present anomalous frequency behavior below a characteristic temperature, T* ∼60-65 K, such as that found for the stretching modes. The sign and magnitude of such anomalous behavior appear to be correlated with the ionic radius of R, being softening for R=Bi and hardening for R=Eu and Dy in the range between TC TN and T*. The anomalous phonon behaviors in both bending and stretching modes are consistent with an interpretation in terms of the spin-phonon coupling in a scenario of strong magnetic correlations. © 2007 American Institute of Physics.1019Wang, J., (2003) Science, 299, p. 1719Hur, N., Park, S., Sharma, P.A., Ahn, J.S., Guha, S., Cheong, S.-W., (2004) Nature (London), 429, p. 392Alonso, J.A., Casais, M.T., Martínez-Lope, M.J., Martínez, J.L., Fernández-Díaz, M.T., (1997) J. Phys.: Condens. Matter, 9, p. 8515Kagomiya, I., Kohn, K., Uchiyama, T., (2002) Ferroelectrics, 280, p. 297Hur, N., Park, S., Sharma, P.A., Guha, S., Cheong, S.-W., (2004) Phys. Rev. Lett., 93, p. 107207Muoz, A., Alonso, J.A., Casais, M.T., Martínez-Lope, M.J., Martínez, J.L., Fernández-Díaz, M.T., (2002) Phys. Rev. B, 65, p. 144423Golovenchits, E.I., Sanina, V.A., Babinskii, A.V., (1997) JETP, 85, p. 156Chapon, L.C., Blake, G.R., Gutmann, M.J., Park, S., Hur, N., Radaelli, P.G., Cheong, S.-W., (2004) Phys. Rev. Lett., 93, p. 177402Blake, G.P., Chapon, L.C., Radaelli, P.G., Park, S., Hur, N., Cheong, S.-W., Rodríguez-Carvajal, J., (2005) Phys. Rev. B, 71, p. 214402Polyakov, V., Plakhty, V., Bonnet, M., Burlet, P., Regnault, L.-P., Gavrilov, S., Zobkalo, I., Smirnov, O., (2001) Physica B, 297, p. 208Higashiyama, D., Miyasaka, S., Kida, N., Arima, T., Tokura, Y., (2004) Phys. Rev. B, 70, p. 174405Ramirez, A.P., (2001) Handbook of Magnetic Materials, 13, pp. 423-520. , Elsevier, New YorkGarcía-Flores, A.F., (2006) Phys. Rev. B, 73, p. 104411Baltensperger, W., Helman, J.S., (1968) Helv. Phys. Acta, 41, p. 668Granado, E., (2001) Phys. Rev. Lett., 86, p. 5385Sushkov, A.B., Tchernyshyov, O., Ratcliff, I.I.W., Cheong, S.-W., Drew, H.D., (2004) Phys. Rev. Lett., 94, p. 13720

Anomalous Phonon Shifts In The Paramagnetic Phase Of Multiferroic R Mn2 O5 (r=bi, Eu, Dy): Possible Manifestations Of Unconventional Magnetic Correlations

A Raman spectroscopic study of the high-frequency optical phonons in single crystals of the multiferroic system R Mn2 O5 (R=Bi, Eu, Dy) was performed. All studied materials show anomalous phonon shifts, below a new characteristic temperature for these materials, T* ∼60-65 K. The sign and magnitude of such shifts appear to be correlated with the ionic radius of R, envolving from softenings for R=Bi to hardenings for R=Dy and showing an intermediary behavior for R=Eu. Additional phonon anomalies were identified below ∼ TN ∼40-43 K, reflecting the onset of long-range ferroelectric and/or magnetic order of the Mn sublattice. Complementary dc-magnetic susceptibility [χ (T)] measurements for Bi Mn2 O5 up to 800 K yield a Curie-Weiss temperature θCW =-253 (3) K, revealing a fairly large frustration ratio (θCW TN =6.3). 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Perspectives on carbon materials as powerful catalysts in continuous anaerobic bioreactors

Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.watres.2016.06.004.The catalytic effect of commercial microporous activated carbon (AC) and macroporous carbon nanotubes (CNT) is investigated in reductive bioreactions in continuous high rate anaerobic reactors, using the azo dye Acid Orange 10 (AO10) as model compound as electron acceptor and a mixture of VFA as electron donor. Size and concentration of carbon materials (CM) and hydraulic retention time (HRT) are assessed. CM increased the biological reduction rate of AO10, resulting in significantly higher colour removal, as compared to the control reactors. The highest efficiency, 98%, was achieved with a CNT diameter (d) lower than 0.25 mm, at a CNT concentration of 0.12 g per g of volatile solids (VS), a HRT of 10 h and resulted in a chemical oxygen demand (COD) removal of 85%. Reducing the HRT to 5 h, colour and COD removal in CM-mediated bioreactors were above 90% and 80%, respectively. In the control reactor, thought similar COD removal was achieved, AO10 decolourisation was just approximately 20%, demonstrating the ability of CM to significantly accelerate the reduction reactions in continuous bioreactors. AO10 reduction to the correspondent aromatic amines was proved by high performance liquid chromatography (HPLC). Colour decrease in the reactor treating a real effluent with CNT was the double comparatively to the reactor operated without CNT. The presence of AC in the reactor did not affect the microbial diversity, as compared to the control reactor, evidencing that the efficient reduction of AO10 was mainly due to AC rather than attributed to changes in the composition of the microbial communities.This study was supported by the Portuguese Foundation for Science and Technology (FCT) under the scope of the strategic funding of UID/BIO/04469/2013 unit and COMPETE 2020 (POCI-01- 0145-FEDER-006684). Raquel Pereira had a fellowship (SFRH/BD/ 72388/2010) and Luciana Pereira has the fellowship (SFRH/BPD/ 110235/2015) from FCT. The authors thank the FCT exploratory EXPL/AAG-TEC/0898/2013 project

Far-infrared optical excitations in multiferroic TbMnO_3

We provide a detailed study of the reflectivity of multiferroic TbMnO_3 for wave numbers from 40 cm^{-1} to 1000 cm^{-1} and temperatures 5 K < T < 300 K. Excitations are studied for polarization directions E || a, the polarization where electromagnons are observed, and for E || c, the direction of the spontaneous polarization in this material. The temperature dependencies of eigenfrequencies, damping constants and polar strengths of all modes are studied and analyzed. For E || a and below the spiral ordering temperature of about 27 K we observe a transfer of optical weight from phonon excitations to electromagnons, which mainly involves low-frequency phonons. For E || c an unusual increase of the total polar strength and hence of the dielectric constant is observed indicating significant transfer of dynamic charge probably within manganese-oxygen bonds on decreasing temperatures.Comment: 8 pages, 7 figures, accepted for submission in European Physical Journal

Search for a W' boson decaying to a bottom quark and a top quark in pp collisions at sqrt(s) = 7 TeV

Results are presented from a search for a W' boson using a dataset corresponding to 5.0 inverse femtobarns of integrated luminosity collected during 2011 by the CMS experiment at the LHC in pp collisions at sqrt(s)=7 TeV. The W' boson is modeled as a heavy W boson, but different scenarios for the couplings to fermions are considered, involving both left-handed and right-handed chiral projections of the fermions, as well as an arbitrary mixture of the two. The search is performed in the decay channel W' to t b, leading to a final state signature with a single lepton (e, mu), missing transverse energy, and jets, at least one of which is tagged as a b-jet. A W' boson that couples to fermions with the same coupling constant as the W, but to the right-handed rather than left-handed chiral projections, is excluded for masses below 1.85 TeV at the 95% confidence level. For the first time using LHC data, constraints on the W' gauge coupling for a set of left- and right-handed coupling combinations have been placed. These results represent a significant improvement over previously published limits.Comment: Submitted to Physics Letters B. Replaced with version publishe

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Reducing heterotic M-theory to five dimensional supergravity on a manifold with boundary

This paper constructs the reduction of heterotic $M$-theory in eleven dimensions to a supergravity model on a manifold with boundary in five dimensions using a Calabi-Yau three-fold. New results are presented for the boundary terms in the action and for the boundary conditions on the bulk fields. Some general features of dualisation on a manifold with boundary are used to explain the origin of some topological terms in the action. The effect of gaugino condensation on the fermion boundary conditions leads to a `twist' in the chirality of the gravitino which can provide an uplifting mechanism in the vacuum energy to cancel the cosmological constant after moduli stabilisation.Comment: 16 pages, RevTe

Measurement of the inclusive isolated prompt photon cross-section in pp collisions at sqrt(s)= 7 TeV using 35 pb-1 of ATLAS data

A measurement of the differential cross-section for the inclusive production of isolated prompt photons in pp collisions at a center-of-mass energy sqrt(s) = 7 TeV is presented. The measurement covers the pseudorapidity ranges |eta|<1.37 and 1.52<=|eta|<2.37 in the transverse energy range 45<=E_T<400GeV. The results are based on an integrated luminosity of 35 pb-1, collected with the ATLAS detector at the LHC. The yields of the signal photons are measured using a data-driven technique, based on the observed distribution of the hadronic energy in a narrow cone around the photon candidate and the photon selection criteria. The results are compared with next-to-leading order perturbative QCD calculations and found to be in good agreement over four orders of magnitude in cross-section.Comment: 7 pages plus author list (18 pages total), 2 figures, 4 tables, final version published in Physics Letters