Absence of Edge Localized Moments in the Doped Spin-Peierls System CuGe1−x_{1-x}Six_{x}O3_3

We report the observation of nuclear quadrupole resonance (NQR) of Cu from the sites near the doping center in the spin-Peierls system CuGe$_{1-x}$Si$_{x}$O$_3$. The signal appears as the satellites in the Cu NQR spectrum, and has a suppressed nuclear spin-lattice relaxation rate indicative of a singlet correlation rather than an enhanced magnetic correlation near the doping center. Signal loss of Cu nuclei with no neighboring Si is also observed. We conclude from these observations that the doping-induced moments are not in the vicinity of the doping center but rather away from it.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Let

Catalytic carbonization of wood charcoal:graphite or diamond?

We report on the process of making graphite out of wood by catalytic carbonization. Two different types of microstructure were observed. One type being typical for graphitization of wood without the effect of a catalyst, the main characteristic being the typical fibrillar microstructure related back to the original cellulose morphology. A strong {0002} inner diffraction ring corresponding to the 0.336 nm lattice spacing of graphite dominates its diffraction pattern. The other type being typical for graphitization of wood with aluminum as catalyst, the main characteristic being the large sheets of carbon forced upon by the formation of plate like Al4C3. This compound is formed as an intermediate reaction product, which dissociates into aluminum vapour and solid carbon. The diffraction pattern indicates a differently textured structure. EELS measurements in the areas of catalytic graphitization indicate a significant decrease of the sp(2) bonding typical for graphite. It can be an indication of the presence of metastable diamond. This diamond-like structure is extremely unstable under influence of the electron beam. It decomposed within 250 s of beam exposure. (C) 2003 Elsevier Ltd. All rights reserved

The Structure of the X-Ray Emitting Gas in the Hydra-A Cluster of Galaxies

The temperature and abundance structure in the intracluster medium (ICM) of the Hydra-A cluster of galaxies is studied with ASCA and ROSAT. The effect of the large extended outskirts in the point-spread function of the X-Ray Telescope on ASCA is included in this analysis. In the X-ray brightness profile, the strong central excess above a single beta-model, identified in the Einstein and ROSAT data, is also found in the harder energy band (>4keV). A simultaneous fit of five annular spectra taken with the GIS instrument shows a radial distribution of the temperature and metal abundance. A significant central enhancement in the abundance distribution is found, while the temperature profile suggests that the ICM is approximately isothermal with the temperature of ~3.5keV. The ROSAT PSPC spectrum in the central 1'.5 region indicates a significantly lower temperature than the GIS result. A joint analysis of the GIS and PSPC data reveals that the spectra can be described by a two temperature model as well as by a cooling flow model. In both cases, the hot phase gas with the temperature of ~3.5keV occupies more than 90% of the total emission measure within 1'.5 from the cluster center. The estimated mass of the cooler (0.5-0.7keV) component is ~2-6 x 10^9 M_solar, which is comparable to the mass of hot halos seen in non-cD ellipticals. The cooling flow model gives the mass deposition rate of 60+-30 M_solar/yr, an order of magnitude lower than the previous estimation.Comment: 27 pages, 14 figures, AAS LATEX macros v4.0, to appear in The Astrophysical Journa

Toward Identification of Order Parameters in Skutterudites - a Wonderland of Strong Correlation Physics -

Current status is described toward identifying unconventional order parameters in filled skutterudites with unique ordering phenomena. The order parameters in PrFe$_4$P$_{12}$ and PrRu$_4$P$_{12}$ are discussed in relation to associated crystalline electric field (CEF) states and angular form factors. By phenomenological Landau analysis, it is shown that a scalar order model explains most properties in both PrFe$_4$P$_{12}$ and PrRu$_4$P$_{12}$ with very different magnetic properties. In particular, the highly anisotropic susceptibility induced by uniaxial pressure in PrFe$_4$P$_{12}$ is explained in terms of two types of couplings. In the case of SmRu$_4$P$_{12}$, the main order parameter at low field is identified as magnetic octupoles. A microscopic mechanism is proposed how the dipole and octupole degrees of freedom mix under the point group $T_h$ of skutterudites.Comment: To be published in Proc. International Conference on New Quantum Phenomena in Skutterudite and Related Systems (Suppl. J. Phys. Soc. Jpn 78, 2008

1^1H-NMR Study of the Random Bond Effect in the Quantum Spin System (CH3_3)2_2CHNH3_3Cu(Clx_xBr1−x_{1-x})3_3

Spin-lattice relaxation rate $T_1^{-1}$ of $^1$H-NMR has been measured in (CH$_3$)$_2$CHNH$_3$Cu(Cl$_x$Br$_{1-x}$)$_3$ with $x=0.88$, which has been reported to be gapped system with singlet ground state from the previous macroscopic magnetization and specific heat measurements, in order to investigate the bond randomness effect microscopically in the gapped composite Haldane system (CH$_3$)$_2$CHNH$_3$CuCl$_3$. It was found that the spin-lattice relaxation rate $T_1^{-1}$ in the present system includes both fast and slow relaxation parts indicative of the gapless magnetic ground state and the gapped singlet ground state, respectively. We discuss the obtained results with the previous macroscopic magnetization and specific heat measurements together with the microscopic $\mu$SR experiments.Comment: 4 pages, 2 figures, to be published in J. Phys. Soc. Jpn. vol.76 (2007) No.

An ASCA Study of the Heavy Element Distribution in Clusters of Galaxies

We perform a spatially resolved X-ray spectroscopic study of a set of 11 relaxed clusters of galaxies observed by the ROSAT/PSPC and ASCA/SIS. Using a method which corrects for the energy dependent effects of the ASCA PSF based on ROSAT images, we constrain the spatial distribution of Ne, Si, S and Fe in each cluster. Theoretical prescriptions for the chemical yields of Type Ia and II supernovae, then allow determination of the Fe enrichment from both types of supernovae as a function of radius within each cluster. Using optical measurements from the literature, we also determine the iron mass-to-light ratio (IMLR) separately for Fe synthesized in both types of supernovae. For clusters with the best photon statistics, we find that the total Fe abundance decreases significantly with radius, while the Si abundance is either flat or decreases less rapidly, resulting in an increasing Si/Fe ratio with radius. This result indicates a greater predominance of Type II SNe enrichment at large radii in clusters. We suggest that the high Si/Fe ratios in the outskirts of rich clusters may arise from enrichment by Type II SNe released to ICM via galactic star burst driven winds. Abridged.Comment: 17 pages, ApJ in press (Nov. 2000), a study of systematics is adde

Magnetic Phase Diagram and Metal-Insulator Transition of NiS2-xSex

Magnetic phase diagram of NiS2-xSex has been reexamined by systematic studies of electrical resistivity, uniform magnetic susceptibility and neutron diffraction using single crystals grown by a chemical transport method. The electrical resistivity and the uniform magnetic susceptibility exhibit the same feature of temperature dependence over a wide Se concentration. A distinct first order metal-insulator (M-I) transition accompanied by a volume change was observed only in the antiferromagnetic ordered phase for 0.50<x<0.59. In this region, the M-I transition makes substantial effects to the thermal evolution of staggered moments. In the paramagnetic phase, the M-I transition becomes broad; both the electrical resistivity and the uniform magnetic susceptibility exhibit a broad maximum around the temperatures on the M-I transition-line extrapolated to the paramagnetic phase.Comment: 6 pages, 8 figures, corrected EPS fil

Coexistence of double alternating antiferromagnetic chains in (VO)_2P_2O_7 : NMR study

Nuclear magnetic resonance (NMR) of 31P and 51V nuclei has been measured in a spin-1/2 alternating-chain compound (VO)_2P_2O_7. By analyzing the temperature variation of the 31P NMR spectra, we have found that (VO)_2P_2O_7 has two independent spin components with different spin-gap energies. The spin gaps are determined from the temperature dependence of the shifts at 31P and 51V sites to be 35 K and 68 K, which are in excellent agreement with those observed in the recent inelastic neutron scattering experiments [A.W. Garrett et al., Phys. Rev. Lett. 79, 745 (1997)]. This suggests that (VO)_2P_2O_7 is composed of two magnetic subsystems showing distinct magnetic excitations, which are associated with the two crystallographically-inequivalent V chains running along the b axis. The difference of the spin-gap energies between the chains is attributed to the small differences in the V-V distances, which may result in the different exchange alternation in each magnetic chain. The exchange interactions in each alternating chain are estimated and are discussed based on the empirical relation between the exchange interaction and the interatomic distance.Comment: 10 pages, 11 embedded eps figures, REVTeX, Submitted to Phys. Rev.

Mass Profiles of the Typical Relaxed Galaxy Clusters A2199 and A496

We present maps and radial profiles of the gas temperature in the nearby galaxy clusters A2199 and A496, which have the most accurate ASCA spectral data for all hot clusters. These clusters are relaxed and can provide reliable X-ray mass measurements under the assumption of hydrostatic equilibrium. The cluster average temperatures corrected for the presence of cooling flows are 4.8+-0.2 keV and 4.7+-0.2 keV (90% errors), respectively. Outside the central cooling flow regions, the radial temperature profiles are similar to those of the majority of nearby relaxed clusters. They are accurately described by polytropic models with gamma=1.17+-0.07 for A2199 and gamma=1.24+-0.09 for A496. We use these polytropic models to derive accurate total mass profiles. Within r=0.5/h Mpc, which corresponds to a radius of overdensity 1000, the total mass values are 1.45+-0.15 10^14 /h Msun and 1.55+-0.15 10^14 /h Msun. These values are 10% lower than those obtained assuming constant temperature. The values inside a gas core radius (0.07-0.13/h Mpc) are a factor of >1.5 higher than the isothermal values. The gas mass fraction increases with radius (by a factor of 3 between the X-ray core radius and r_1000) and at r_1000 reaches values of 0.057+-0.005 and 0.056+-0.006 h^-3/2 for the two clusters, respectively. Our mass profiles within r_1000 are remarkably well approximated by the NFW "universal" profile. Since A2199 and A496 are typical relaxed clusters, the above findings should be relevant for most such systems. In particular, the similarity of the temperature profiles in nearby clusters appears to reflect the underlying "universal" dark matter profile. The upward revision of mass at small radii will resolve most of the discrepancy between the X-ray and strong lensing mass estimates. (Abridged)Comment: Latex, 9 pages, 6 figures, uses emulateapj.sty. Submitted to Ap

Folding of the Triangular Lattice in the FCC Lattice with Quenched Random Spontaneous Curvature

We study the folding of the regular two-dimensional triangular lattice embedded in the regular three-dimensional Face Centered Cubic lattice, in the presence of quenched random spontaneous curvature. We consider two types of quenched randomness: (1) a ``physical'' randomness arising from a prior random folding of the lattice, creating a prefered spontaneous curvature on the bonds; (2) a simple randomness where the spontaneous curvature is chosen at random independently on each bond. We study the folding transitions of the two models within the hexagon approximation of the Cluster Variation Method. Depending on the type of randomness, the system shows different behaviors. We finally discuss a Hopfield-like model as an extension of the physical randomness problem to account for the case where several different configurations are stored in the prior pre-folding process.Comment: 12 pages, Tex (harvmac.tex), 4 figures. J.Phys.A (in press