Spin liquid in a single crystal of the frustrated diamond lattice antiferromagnet CoAl2O4

We study spin liquid in the frustrated diamond lattice antiferromagnet CoAl2O4 by means of single crystal neutron scattering in zero and applied magnetic field. The magnetically ordered phase appearing below TN=8 K remains nonconventional down to 1.5 K. The magnetic Bragg peaks at the q=0 positions remain broad and their profiles have strong Lorentzian contribution. Additionally, they are connected by weak diffuse streaks along the directions. These observations are explained within the spiral spin liquid model as short-range magnetic correlations of spirals populated at these finite temperatures, as the energy minimum around q=0 is flat and the energy of excited states with q=(111) is low. The agreement is only qualitative, leading us to suspect that microstructure effects are also important. Magnetic field significantly perturbs spin correlations. The 1.5 K static magnetic moment increases from 1.58 mB/Co at zero field to 2.08 mB/Co at 10 T, while the magnetic peaks, being still broad, acquire almost Gaussian profile. Spin excitations are rather conventional spin waves at zero field, resulting in the exchange parameters J1=0.92(1) meV, J2=0.101(2) meV and the anisotropy term D=-0.0089(2) meV for CoAl2O4. The application of a magnetic field leads to a pronounced broadening of the excitations at the zone center, which at 10 T appear gapless and nearly featureless

Assessment of Cement Durability in Repository Environment

Portland cement paste is proposed as the material to filling in the annulus between the casing of a borehole and the geological formation in a deep repository for spent sealed radiation sources in Brazil. The cement paste is intended to function as structural material, an additional barrier against the migration of radionuclides outside the repository, and as a blockage against the transport of water between the different strata of the geological setting. The objective of this research is to investigate the behavior of the cement paste and to estimate its service life. In this paper we present the results of mechanical strength measurements and chemical and mineralogical analysis of samples to detect the changes caused by radiation, temperature and aggressive chemicals of groundwater to which the material will be exposed. Methods of analysis included Inductively Coupled Plasma Atomic Emission Spectroscopy, Ion Chromatography, XRay Diffraction, and Thermo Gravimetric Analysi

Synchrotron powder diffraction study of cements pastes

 Knowledge of the degree of hydration of cement pastes is critical for determining properties such as the durability of concrete. As part of an integrated study on the prediction of chloride ingress in reinforced concrete, synchrotron Xray powder diffraction was used to estimate the degree of hydration of cement pastes. While for the past 20 years the composition of Portland cement has been determined by Rietveld analysis of X-ray diffraction, nevertheless there are a number of factors, including the amorphous content of the cement and relative proportion of mineral polymorphs present in the initial clinker, whose impact on the analysis are still not completely understood. Analysis of the resulting diffraction patterns indicated enhanced identification of polymorphs of alite, belite, ferrite and aluminate, which are present in the initial unhydrated cement and clinker, as well as improved quantification of hydrated crystalline phases such as calcium hydroxide and ettringite, which are key phases determining the speed of the chemical reactions in cement. In this paper we describe the experience that we have gained in the determination of the degree of hydration of cement pastes. We detail the standards and precautions that we took to characterize production cements and their hydration products

Magnetic relaxation of exchange biased (Pt/Co) multilayers studied by time-resolved Kerr microscopy

Magnetization relaxation of exchange biased (Pt/Co)5/Pt/IrMn multilayers with perpendicular anisotropy was investigated by time-resolved Kerr microscopy. Magnetization reversal occurs by nucleation and domain wall propagation for both descending and ascending applied fields, but a much larger nucleation density is observed for the descending branch, where the field is applied antiparallel to the exchange bias field direction. These results can be explained by taking into account the presence of local inhomogeneities of the exchange bias field.Comment: To appear in Physical Review B (October 2005

Writing and reading chiral domains in multiferroic DyMnO_3 using soft X-rays

Sizeable b and c components of the 4f moments and pronounced circular dichroism are observed in the ferroelectric phase of DyMnO_3 by soft X-ray diffraction at the Dy-M_5 resonance. This points to cycloidal order of the 4f moments and indicates that inversion-symmetry breaking in this material is not characteristic of the Mn spins alone. The circular dichroism allows to image chiral domains that are imprinted on the surface of a DyMnO$_3$ single crystal, exploiting the local charging by the X-ray beam via the photoelectric effect. These findings suggest a novel approach to control and image domains and domain walls in multiferroic materials

Spin-driven Phase Transitions in ZnCr2_2Se4_4 and ZnCr2_2S4_4 Probed by High Resolution Synchrotron X-ray and Neutron Powder Diffraction

The crystal and magnetic structures of the spinel compounds ZnCr$_2$S$_4$ and ZnCr$_2$Se$_4$ were investigated by high resolution powder synchrotron and neutron diffraction. ZnCr$_2$Se$_4$ exhibits a first order phase transition at $T_N=21$ K into an incommensurate helical magnetic structure. Magnetic fluctuations above $T_N$ are coupled to the crystal lattice as manifested by negative thermal expansion. Both, the complex magnetic structure and the anomalous structural behavior can be related to magnetic frustration. Application of an external magnetic field shifts the ordering temperature and the regime of negative thermal expansion towards lower temperatures. Thereby, the spin ordering changes into a conical structure. ZnCr$_2$S$_4$ shows two magnetic transitions at $T_{N1}=15$ K and $T_{N2}=8$ K that are accompanied by structural phase transitions. The crystal structure transforms from the cubic spinel-type (space group $Fd$\={3}$m$) at high temperatures in the paramagnetic state, via a tetragonally distorted intermediate phase (space group $I4_1$ / $amd$) for $T_{N2} < T < T_{N1}$ into a low temperature orthorhombic phase (space group $I m m a$) for $T < T_{N2}$. The cooperative displacement of sulfur ions by exchange striction is the origin of these structural phase transitions. The low temperature structure of ZnCr$_2$S$_4$ is identical to the orthorhombic structure of magnetite below the Verwey transition. When applying a magnetic field of 5 T the system shows an induced negative thermal expansion in the intermediate magnetic phase as observed in ZnCr$_2$Se$_4$.Comment: 11 pages, 13 figures, to be published in PR

Anisotropic physical properties of single crystal U2Rh2Sn in high magnetic fields

We report on the crystal and magnetic structures,magnetic, transport, and thermal properties of U2Rh2Sn single crystals studied in part in high magnetic fields up to 58 T. The material adopts a U3Si2 related tetragonal crystal structure and orders antiferromagnetically below TN 25 K. The antiferromagnetic structure is characterized by a propagation vector k 0,0,1 2 . The magnetism in U2Rh2Sn is found to be associated mainly with 5f states. However, both unpolarized and polarized neutron experiments reveal at low temperatures in zero field non negligible magnetic moments also on Rh sites. U moments of 0.50 2 amp; 956;B are directed along the tetragonal axis while Rh moments of 0.06 4 amp; 956;B form a noncollinear arrangement confined to the basal plane. The response to applied magnetic field is highly anisotropic. Above amp; 8764;15 K the easy magnetization direction is along the tetragonal axis. At lower temperatures, however, a stronger response is found perpendicular to the c axis. While for the a axis no magnetic phase transition is observed up to 58 T, for the field applied at 1.8 K along the tetragonal axis we observe above 22.5 T a field polarized state. A magnetic phase diagram for the field applied along the c axis is presented

Inclusion Complex Of S(-) Bupivacaine And 2-hydroxypropyl- β-cyclodextrin: Study Of Morphology And Cytotoxicity

Local anesthetics (LA) belong to a class of pharmacological compounds that attenuate or eliminate pain by binding to the sodium channel of excitable membranes, blocking the influx of sodium ions and the propagation of the nerve impulse. S (-) bupivacaine (S(-) bvc) is a local anesthetic of amino-amide type, widely used in surgery and obstetrics for sustained peripheral and central nerve blockade. This article focuses on the characterization of an inclusion complex of S(-) bvc in 2-hydroxypropyl-β-cyclodextrin (HP-β-CD). Differential scanning calorimetry, scanning electron microscopy and X-Ray diffraction analysis showed structural changes in the complex. In preliminary toxicity studies, the cell viability tests revealed that the inclusion complex decreased the toxic effect (p<0.001) produced by S(-) bvc. These results suggest that the S(-) bvc:HP-β-CD inclusion complex represents a promising agent for the treatment of regional pain.273207212Araújo, D.R., Cereda, C.M., Brunetto, G.B., Pinto, L.M.A., Santana, M.H., de Paula, E., Encapsulation of mepivacaine prolongs the analgesia provided by sciatic nerve blockade in mice (2004) Can J Anaesth, 51, pp. 566-572Araújo, D.R., Fraceto, L.F., Braga, A.F.A., de Paula, E., Drug-delivery systems for racemic bupivacaine (S50-R50) and bupivacaine enantiomeric mixture (S75-R25):cyclodextrins complexation effects on sciatic nerve blockade in mice (2005) Rev Bras Anestesiol, 55, pp. 316-328Araújo, D.R., Moraes, C.M., Fraceto, L.F., Braga, A.F.A., de Paula, E., Cyclodextrin-bupivacaine enantiomeric mixture (S75-R25) inclusion complex and intrathecal anesthesia in rats (2006) Rev Bras Anestesiol, 56, pp. 495-506Bibby, D., Davies, N.M., Tueker, I.G., Mechanisms by which cyclodextrins modify drug release from polymeric drug delivery systems (2000) Int J Pharm, 197, pp. 1-11Covino, B.G., Vassalo, H.G., (1976) Local anesthetics: Mechanisms of action and clinical use, , New York: Grune and Stratton;, 255pFoster, R.H., Markham, A., Levobupivacaine. A review of its pharmacology and use as a local anaesthetic (2000) Drugs, 59, pp. 551-579Grant, G.J., Bansinath, M., Liposomal delivery systems for local anesthetics (2001) Reg Anesth Pain Med, 26, pp. 61-63Gristwood, R.W., Cardiac and CNS toxicity of levobupivacaine: Strengths of evidence for advantage over bupivacaine (2002) Drug Saf, 25, pp. 153-163Hirayama, F., Uekama, K., Cyclodextrin-based controlled drug release system (1999) Adv Drug Deliv Rev, 36, pp. 125-141Huang, Y.F., Pryor, M.E., Mather, L.E., Veering, B.T., Cardiovascular and central nervous system effects of intravenous S-bupivacaine and bupivacaine in sheep (1998) Anesth Analg, 86, pp. 797-804Jong, R.H., (1994) Local anesthetics, , Springfield: CC. Thomas;, 325pKohata, S., Jyodi, K., Ohyoshi, A., Thermal decomposition of cyclodextrins (α -, β-, γ, and modified β-CyD) and of metal-(β-CyD) complex in the solid phase (1993) Thermochim Acta, 217, pp. 187-198Loftsson, T., Brewster, M.E., Pharmaceutical application of Cyclodextrin. 1. Drug solubilization and stabilization (1996) J Pharm Sci, 85, pp. 1017-1025Loukas, Y.L., Vraka, V., Gregoriadis, G., Novel non-acidic formulations of haloperidol complexed with beta-cyclodextrin derivatives (1997) J Pharm Biomed Anal, 16, pp. 263-268Mather, L.E., McCall, P., McNicol, P.L., Bupivacaine enantiomer pharmacokinetics after intercostal neural blockade in liver transplant patients (1995) Anesth Analg, 80, pp. 328-335Michaud, M., Icart, S., Determination of the substitution of hydroxypropylbetadex using fourier transform infrared spectrophotometry (2001) PharmEuropa, 13, pp. 714-716Naidu, N.B., Chowdary, K.P.R., Murthy, K.V.R., Satyanarayana, V., Hayman, A.R., Becket, G., Physicochemical characterization and dissolution properties of meloxicam-cyclodextrin binary systems (2004) J Pharm Biomed Anal, 35, pp. 75-86Pinto, L.M.A., Fraceto, L.F., Santana, M.H.A., Pertinhez, T.A., Oyama, S., de Paula, E., Physico-chemical characterization of benzocaine-β-cyclodextrin inclusion complexes (2005) J Pharm Biomed Anal, 39, pp. 956-963Ren, X., Xue, Y., Liu, J., Zhang, K., Zheng, J., Lou, G., Gou, C., Shen, J., A novel cyclodextrin-deri ved tellurium compound with glutathione peroxidase (2002) Chembiochem, 3, pp. 363-365Rose, J.S., Neal, J.M., Kopacz, D.J., Extended-duration analgesia: Update on microspheres and liposomes (2005) Reg Anesth Pain Med, 30, pp. 275-285Strichartz, G.R., Ritchie, J.M., (1987) Local anesthetics: Handbook of experimental pharmacology, , Berlin: Springer-Verlag;, 445pThompson, D.O., Cyclodextrin-enabling excipients: Their present and future use in pharmaceuticals (1997) Crit Rev Ther Drug Carrier Syst, 14, pp. 1-10