Magnetic dichroism study on Mn1.8_{1.8}Co1.2_{1.2}Ga thin film using a combination of X-ray absorption and photoemission spectroscopy

Using circularly polarised radiation and a combination of bulk-sensitive hard X-ray photoelectron spectroscopy and X-ray-absorption spectroscopy (XAS) we studied the electronic and magnetic structure of epitaxial Mn$_{1.8}$Co$_{1.2}$Ga thin films. Spin resolved Bloch spectral functions, density of states as well as charge and magnetisation densities were investigated by a first-principles analysis of full potential, fully relativistic Korringa--Kohn--Rostoker calculations of the electronic structure. The valence states were experimentally investigated by using linear dichroism in the angular distribution and comparing the results to spin-resolved densities of states. The linear dichroism in the valence band enabled a symmetry analysis of the contributing states. The spectra were in good agreement with the theoretical partial density of states. The element-specific, spin-resolved, unoccupied densities of states for Co and Mn were analysed by using XAS and X-ray magnetic circular dichroism (XMCD) at the $L_{3,2}$ edges. The spectra were influenced by strong correlation effects. XMCD was used to extract the site resolved magnetic moments. The experimental values of $m_{\rm Mn}=0.7\:\mu_B$ and $m_{\rm Co}=1.05\:\mu_B$ agree very well with the calculated magnetic moments. Magnetic circular dichroism in angle-resolved photoelectron spectroscopy at the Mn and Co $2p$ core level exhibited a pronounced magnetic dichroism and confirmed the localised character of the Mn $d$ valence states

Magnetic and transport properties of tetragonal- or cubic-Heusler-type Co-substituted Mn-Ga epitaxial thin films

The composition dependence of the structural, magnetic, and transport properties of epitaxially grown Mn-Co-Ga films were investigated. The crystal structure was observed to change from tetragonal to cubic as the Co content was increased. In terms of the dependence of saturation magnetization on the Co content, relatively small value was obtained for the Mn$_{2.3}$Co$_{0.4}$Ga$_{1.3}$ film at a large {\it K}$_\textrm u$ value of 9.2 Merg/cm$^3$. Electrical resistivity of Mn-Co-Ga films was larger than that of pure Mn-Ga film. The maximum value of the resistivity was 490 $\mu\Omega$cm for Mn$_{2.2}$Co$_{0.6}$Ga$_{1.2}$ film. The high resistivity of Mn-Co-Ga might be due to the presence of localized electron states in the films due to chemical disordering caused by the Co substitution.Comment: 3 pages, 5 figures. The article has been submitted to the Journal of Applied Physics as a Proceedings for the 12th Joint MMM/INTERMAG conferenc

Perpendicularly magnetized Mn-Co-Ga-based thin films with high coercive field

Mn$_{3-x}$Co$_{x}$Ga epitaxial thin films were grown on MgO substrates by magnetron co-sputtering. Structures were tetragonal or cubic depending on Co content. Composition dependence of saturation magnetization and uniaxial magnetic anisotropy $K_u$ of the films were investigated. A high $K_u$ (1.2 MJ m$^{-3}$) was achieved for the Mn$_{2.6}$Co$_{0.3}$Ga$_{1.1}$ film with the magnetic moment 0.84$\mu_B$. Valence band spectra were obtained by hard X-ray photoelectron spectroscopy. Sharp peaks in the cubic case, which were absent in the tetragonal case, prove that a van Hove singularity causes a band Jahn-Teller effect with tetragonal distortion. Observations agree well with the first-principles calculations

Electronic structures of B-2p and C-2p of boron-doped diamond film by soft X-ray absorption and emission spectroscopy

X-ray absorption (XAS) and emission (XES) spectroscopy near B-K and C-K edges have been performed on metallic (~1at%B, B-diamond) and semiconducting (~0.1at%B and N, BN-diamond) doped-diamond films. Both B-K XAS and XES spectra shows metallic partial density of state (PDOS) with the Fermi energy of 185.3 eV, and there is no apparent boron-concentration dependence in contrast to the different electric property. In C-K XAS spectrum of B-diamond, the impurity state ascribed to boron is clearly observed near the Fermi level. The Fermi energy is found to be almost same with the top of the valence band of non-doped diamond, E_V, 283.9 eV. C-K XAS of BN-diamond shows both the B-induced shallow level and N-induced deep-and-broad levels as the in-gap states, in which the shallow level is in good agreement with the activation energy (E_a=0.37 eV) estimated from the temperature dependence of the conductivity, namely the change in C-2p PDOS of impurity-induced metallization is directly observed. The electric property of this diamond is mainly ascribed to the electronic structure of C-2p near the Fermi level. The observed XES spectra are compared with the DVX-alpha cluster calculation. The DVX-alpha result supports the strong hybridization between B-2p and C-2p observed in XAS and XES spectra, and suggests that the small amount of borons (<1at%) in diamond occupy the substitutional site rather than interstitial site.Comment: submitted to Phys. Rev. B, 5 pages and 5 figure

Nucleon structure with two flavors of dynamical domain-wall fermions

We present a numerical lattice quantum chromodynamics calculation of isovector form factors and the first few moments of the isovector structure functions of the nucleon. The calculation employs two degenerate dynamical flavors of domain-wall fermions, resulting in good control of chiral symmetry breaking. Non-perturbative renormalization of the relevant quark currents is performed where necessary. The inverse lattice spacing, $a^{-1}$, is about 1.7 GeV. We use degenerate up and down dynamical quark masses around 1, 3/4 and 1/2 the strange quark mass. The physical volume of the lattice is about $(1.9{fm})^3$. The ratio of the isovector vector to axial charges, $g_A/g_V$, trends a bit lower than the experimental value as the quark mass is reduced toward the physical point. We calculate the momentum-transfer dependences of the isovector vector, axial, induced tensor and induced pseudoscalar form factors. The Goldberger-Treiman relation holds at low momentum transfer and yields a pion-nucleon coupling, $g_{\pi NN} = 15.5(1.4)$, where the quoted error is only statistical. We find that the flavor non-singlet quark momentum fraction $_{u-d}$ and quark helicity fraction $_{\Delta u-\Delta d}$ overshoot their experimental values after linear chiral extrapolation. We obtain the transversity, $_{\delta u-\delta d} = 0.93(6)$ in $\bar{\rm MS}$ at 2 GeV and a twist-3 polarized moment, $d_1$, appears small, suggesting that the Wandzura-Wilczek relation holds approximately. We discuss the systematic errors in the calculation, with particular attention paid to finite-volume effects, excited-state contamination, and chiral extrapolations.Comment: 28 pages in two columns; 37 figures, 12 table

Charm as a domain wall fermion in quenched lattice QCD

We report a study describing the charm quark by a domain-wall fermion (DWF) in lattice quantum chromodynamics (QCD). Our study uses a quenched gauge ensemble with the DBW2 rectangle-improved gauge action at a lattice cutoff of $a^{-1} \sim 3$ GeV. We calculate masses of heavy-light (charmed) and heavy-heavy (charmonium) mesons with spin-parity $J^P = 0^\mp$ and $1^\mp$, leptonic decay constants of the charmed pseudoscalar mesons ($D$ and $D_s$), and the $D^0$-$\bar{D^0}$ mixing parameter. The charm quark mass is found to be $m^{\bar{\rm MS}}_{c}(m_{c})=1.24(1)(18)$ GeV. The mass splittings in charmed-meson parity partners $\Delta_{q,J=0}$ and $\Delta_{q, J=1}$ are degenerate within statistical errors, in accord with experiment, and they satisfy a relation $\Delta_{q=ud, J} > \Delta_{q=s, J}$, also consistent with experiment. A C-odd axial vector charmonium state, $h_c), lies 22(11) MeV above the$\chi_{c1}$meson, or$m_{h_{c}} = 3533(11)_{\rm stat.}$MeV using the experimental$\chi_{c1}) mass. However, in this regard, we emphasize significant discrepancies in the calculation of hyperfine splittings on the lattice. The leptonic decay constants of $D$ and $D_s$ mesons are found to be $f_D=232(7)_{\rm stat.}(^{+6}_{-0})_{\rm chiral}(11)_{\rm syst.}$ MeV and $f_{D_s}/f_{D} = 1.05(2)_{\rm stat.}(^{+0}_{-2})_{\rm chiral}(2)_{\rm syst.}$, where the first error is statistical, the second a systematic due to chiral extrapolation and the third error combination of other known systematics. The $D^0$-$\bar{D^0}$ mixing bag parameter, which enters the $\Delta C = 2$ transition amplitude, is found to be $B_D(2{GeV})=0.845(24)_{\rm stat.}(^{+24}_{-6})_{\rm chiral}(105)_{\rm syst.}$.Comment: 49 pages, 15 figure

Continuum Limit of BKB_K from 2+1 Flavor Domain Wall QCD

We determine the neutral kaon mixing matrix element $B_K$ in the continuum limit with 2+1 flavors of domain wall fermions, using the Iwasaki gauge action at two different lattice spacings. These lattice fermions have near exact chiral symmetry and therefore avoid artificial lattice operator mixing. We introduce a significant improvement to the conventional NPR method in which the bare matrix elements are renormalized non-perturbatively in the RI-MOM scheme and are then converted into the MSbar scheme using continuum perturbation theory. In addition to RI-MOM, we introduce and implement four non-exceptional intermediate momentum schemes that suppress infrared non-perturbative uncertainties in the renormalization procedure. We compute the conversion factors relating the matrix elements in this family of RI-SMOM schemes and MSbar at one-loop order. Comparison of the results obtained using these different intermediate schemes allows for a more reliable estimate of the unknown higher-order contributions and hence for a correspondingly more robust estimate of the systematic error. We also apply a recently proposed approach in which twisted boundary conditions are used to control the Symanzik expansion for off-shell vertex functions leading to a better control of the renormalization in the continuum limit. We control chiral extrapolation errors by considering both the NLO SU(2) chiral effective theory, and an analytic mass expansion. We obtain B_K^{\msbar}(3 GeV) = 0.529(5)_{stat}(15)_\chi(2)_{FV}(11)_{NPR}. This corresponds to $\hat{B}_K = 0.749(7)_{stat}(21)_\chi(3)_{FV}(15)_{NPR}$. Adding all sources of error in quadrature we obtain $\hat{B}_K = 0.749(27)_{combined}$, with an overall combined error of 3.6%.Comment: 65 page

Light Hadron Spectrum in Quenched Lattice QCD with Staggered Quarks

Without chiral extrapolation, we achieved a realistic nucleon to (\rho)-meson mass ratio of (m_N/m_\rho = 1.23 \pm 0.04 ({\rm statistical}) \pm 0.02 ({\rm systematic})) in our quenched lattice QCD numerical calculation with staggered quarks. The systematic error is mostly from finite-volume effect and the finite-spacing effect is negligible. The flavor symmetry breaking in the pion and (\rho) meson is no longer visible. The lattice cutoff is set at 3.63 (\pm) 0.06 GeV, the spatial lattice volume is (2.59 (\pm) 0.05 fm)(^3), and bare quarks mass as low as 4.5 MeV are used. Possible quenched chiral effects in hadron mass are discussed.Comment: 5 pages and 5 figures, use revtex

Localization and chiral symmetry in 2+1 flavor domain wall QCD

We present results for the dependence of the residual mass of domain wall fermions (DWF) on the size of the fifth dimension and its relation to the density and localization properties of low-lying eigenvectors of the corresponding hermitian Wilson Dirac operator relevant to simulations of 2+1 flavor domain wall QCD. Using the DBW2 and Iwasaki gauge actions, we generate ensembles of configurations with a $16^3\times 32$ space-time volume and an extent of 8 in the fifth dimension for the sea quarks. We demonstrate the existence of a regime where the degree of locality, the size of chiral symmetry breaking and the rate of topology change can be acceptable for inverse lattice spacings $a^{-1} \ge 1.6$ GeV.Comment: 59 Pages, 23 figures, 1 MPG linke

Laxative effects of agarwood on low-fiber diet-induced constipation in rats

<p>Abstract</p> <p>Background</p> <p>Agarwood (<it>Aquilaria sinensis</it>), well known as incense in Southeast Asia, has been used as a digestive in traditional medicine. We investigated the laxative effects of an ethanol extract of agarwood leaves (EEA) in a rat model of low-fiber diet-induced constipation.</p> <p>Methods</p> <p>A set of rats was bred on a normal diet while another set was placed on a low-fiber diet to induce constipation. The laxative effect of agarwood was then investigated on both sets of rats.</p> <p>Results</p> <p>Pretreatment of normal rats with single dose of EEA (600 mg/kg, p.o.) significantly increased frequency and weight of stools. Also, treatments with EEA (300 and 600 mg/kg, p.o.) for 14 days caused a significant increase in stool frequency and weight. Feeding of the animals with a low-fiber diet resulted in a decrease in stool weight, frequency, and water content and also delayed carmine egestion. A single treatment with EEA (600 mg/kg) or senna (150 and 300 mg/kg) significantly increased stool frequency, weight, and water content and also accelerated carmine egestion in the model rats. Once daily administrations of EEA (150 mg/kg), for 14 days, caused a significant increase in water content of stools. The higher doses of EEA (300 and 600 mg/kg) significantly increased frequency, weight, and water content of the stools while accelerating carmine egestion in the constipated rats. Senna (150 and 300 mg/kg) produced similar effect as the higher doses of EEA but, in addition, induced severe diarrhea.</p> <p>Conclusion</p> <p>These findings indicate that EEA has a laxative effect, without causing diarrhea, in a rat model of low-fiber diet-induced constipation. These findings suggest that EEA may be highly effective on constipation as a complementary medicine in humans suffering from life style-induced constipation.</p