Showing papers in "Physica B-condensed Matter in 2000"
TL;DR: In this article, a combination of simulated annealing and representation analysis is used for the determination of magnetic structures from neutron diffraction data, which is a powerful new protocol for determining magnetic structures.
Abstract: The determination of magnetic structures from neutron diffraction data is often carried out by trial and error. Much time is wasted in the examination of structures that are in fact symmetry forbidden. The technique of representation analysis (RA) uses simple matrix calculations to provide model magnetic structures that can arise from a second-order phase transition, but has fallen into misuse because of its tedious nature. New Windows-based code performs these calculations automatically. Integration with refinement packages based on simulated annealing (SA) algorithms allows these models to be fitted against diffraction data. Combination of simulated annealing and representation analysis creates a powerful new protocol for the determination of magnetic structures.
450 citations
TL;DR: In this article, a powder diffractometer for thermal neutrons at the Swiss spallation neutron source SINQ is presented, based on a linear position-sensitive 3 He detector with 1600 wires and angular separation of 0.1°.
Abstract: Design characteristics and first experience concerning the new high-resolution powder diffractometer for thermal neutrons at the Swiss spallation neutron source SINQ are summarized. It is based on a linear position-sensitive 3 He detector with 1600 wires and angular separation of 0.1°, permitting also real-time experiments.
275 citations
TL;DR: In this article, the authors derived the Judd-Ofelt intensity parameters from the integrated absorption spectra and also from the emission spectra under various constraints, and compared the predicted values of τR and βR with the measured values for 5 D 0 level.
Abstract: Optical absorption, excitation and emission spectra of Eu3+ ions in lithium borate and lithium fluoroborate glasses have been investigated. Judd–Ofelt intensity parameters are derived from the integrated absorption spectra and also from the emission spectra under various constraints. The relative merits of thermal correction to the oscillator strengths of the transitions originating from the ground state ( 7 F 0 ) of Eu3+ ion observed in the absorption spectra have been discussed. The Judd–Ofelt parameters obtained from the emission spectra have been used to calculate the total spontaneous emission probabilities (A), lifetimes (τR) and branching ratios (βR) for eight excited levels that include, 5 K 6 , 3 P 0 , 5 H 3 , 5 L 7 , 5 D 3 , 5 D 2 , 5 D 1 and 5 D 0 . The predicted values of τR and βR are compared with the measured values for 5 D 0 level. The stimulated emission cross-sections (σ (λp)) are also evaluated for the 5 D 0 → 7 F J and 5 D 1 → 7 F J transitions. The variation of optical properties with compositional changes of lithium oxide and lithium fluoride contents in the glasses are discussed and compared with similar results.
214 citations
TL;DR: In this paper, the authors reported the observation of molecular layering in a liquid at the solid-liquid interface, using X-ray reflectivity, using tetrakis (2-ethylhexoxy) silane (TEHOS), which is nonpolar and insulating.
Abstract: We report the observation of molecular layering in a liquid at the solid-liquid interface, using X-ray reflectivity. The liquid was tetrakis (2-ethylhexoxy) silane (TEHOS), which is nonpolar and insulating, with spherical molecules of about 10 A diameter. We studied both thin (45–90 A) and relatively thick (∼5000 A) films, which are prepared by dipping in a dilute solution and by pouring and draining the pure material, respectively. For 45–90 A thick films, three layers of density oscillations are seen near the solid–liquid interface, with a spacing comparable to the molecular size. There is an inverse dependence on the substrate surface roughness. For ∼5000 A thick films, we observed a diffraction peak with a correlation length of ∼32 A.
185 citations
TL;DR: A package for analysing μSR data has been developed for the PC running Microsoft Windows operating systems (Windows 95, 98 and NT4) and appropriate features should be included for both pulsed and continuous muon sources.
Abstract: A package for analysing μSR data has been developed for the PC running Microsoft Windows operating systems (Windows 95, 98 and NT4). Some of the key points considered in the design of the program were that it should run on a typical Windows PC, that it should directly read the binary files produced by muon data acquisition systems, that it should be equally easy to analyse data on-line and off-line and that appropriate features should be included for both pulsed and continuous muon sources.
155 citations
TL;DR: In this article, electrical resistivity and thermal conductivity of polypropylene (PP) filled with vapour grown carbon fibre (VGCF) was studied for a wide range of fiber content and compared to systems produced under the same conditions in which a conventional carbon fibre was used as filler.
Abstract: DC electrical resistivity and thermal conductivity of polypropylene (PP) filled with vapour grown carbon fibre (VGCF) was studied. This was done for a wide range of fibre content and compared to systems produced under the same conditions in which a conventional carbon fibre was used as filler. The composites studied exhibit characteristic percolating behaviour. Because of the low degree of graphite perfection in the VGCF used in this work, the fraction of VGCF required to achieve percolation was higher than expected. Non-linear I – V characteristics and time dependent electrical resistivity effects are only observed in PP filled with VGCF. Several mechanisms must be called upon to explain the observed electrical behaviour of the PP/VGCF composite. The thermal conductivity of the composites is in agreement with the effective medium theories.
108 citations
TL;DR: In this article, the optical properties of the broad absorption region due to asymmetric stretching vibration of bridging oxygen in the amorphous structure of bulk SiO 2 were studied.
Abstract: The optical properties of the broad absorption region due to asymmetric stretching vibration of bridging oxygen in the amorphous structure of bulk SiO 2 were studied. The complex refractive index of thick densified chemical-vapour-deposited silicon oxide film was calculated and used further to obtain the dielectric response function of the sample. Vibrational modes were analysed by energy-loss functions for transverse and longitudinal optical phonons. In the 900–1300 cm −1 spectral region, three vibrational modes with well-resolved TO–LO phonon splitting were obtained. The phonon spectra appears as the smeared-out version of the crystalline counterpart, i.e. the α-quartz. The most intense phonon couple at 1064 (TO), and 1248 cm −1 (LO) has the smallest damping and appears to be more crystalline-like than the remaining two. The broad frequency distribution of lattice-like phonon lines gives rise to frequency-dependent damping where the phonons only purely feel each other and have different phonon decays.
108 citations
TL;DR: In this article, a laser Mach-Zehnder interferometeric technique is applied to measure the refractive index n and its thermo-optic coefficient d n /d T for five important pure polar dielectric laser dye solvents (water, methanol, ethyleneglycol, butanol and acetic acid).
Abstract: A laser Mach–Zehnder interferometeric technique is applied to measure the refractive index n and its thermo-optic coefficient d n /d T for five important pure polar dielectric laser dye solvents (water, methanol, ethyleneglycol, butanol and acetic acid). The measurements are carried out using the argon-ion laser wavelength 514.5 nm, and He–Ne laser of λ =632.8 nm. Applying the empirical relationship of Cauchy between the refractive index and wavelength, the following properties are calculated and represented: The refractive index, the thermo-optic constant −d n /d T , the optical dispersion −d n /d λ as a function of wavelength and Cauchy's constants against temperature. On the other hand, a discussion for comparison between the investigated solvents are given.
103 citations
TL;DR: In this article, an experimental investigation of the free decay of quantized turbulence in isotopically pure superfluid 4He at mK temperatures is discussed, and preliminary results suggest the existence of a temperature-independent vortex decay mechanism below T∼70 mK.
Abstract: An experimental investigation of the free decay of quantized turbulence in isotopically pure superfluid 4He at mK temperatures is discussed. Vortices are created by a vibrating grid, and detected by their trapping of negative ions. Preliminary results suggest the existence of a temperature-independent vortex decay mechanism below T∼70 mK .
90 citations
TL;DR: In this article, a near-field surface-plasmon activated device (SPADE) was fabricated on an optic fiber and demonstrated large transmission through a subwavelength aperture.
Abstract: The optical transmission through a subwavelength aperture in a metal film is strongly enhanced when the incident light interacts resonantly with surface plasmons on the surface of the metal. Such interactions are made allowed by a periodic corrugation of the metal surface. We apply this principle on a near-field surface-plasmon activated device (SPADE) fabricated on an optic fiber, and demonstrate large transmission through a subwavelength aperture.
82 citations
TL;DR: In contrast to X-rays, neutrons can penetrate most metals easily as mentioned in this paper, and their high sensitivity for hydrogen makes them a valuable tool for the detection of organic materials like lubricants, plastics or sealants within metal housings.
Abstract: In contrast to X-rays, neutrons can penetrate most metals easily. Neutron attenuation is strongly isotope dependent, and a high contrast is possible for many light-weight elements. Especially their high sensitivity for hydrogen makes them a valuable tool for the detection of organic materials like lubricants, plastics or sealants within metal housings. Neutron radiography and tomography complement the application of X-rays for the inspection of complex and critical components like in automotive and aerospace applications. However, the requirements for beam geometry are much higher for tomography than for simple radiography because the sample cannot be close to the detector, as the sample has to be rotated in the beam, usually by 180°. This paper gives an overview on tomography requirements and limitations, applications and future prospects.
TL;DR: In this paper, three-dimensional photonic crystals operating at optical wavelength region are developed with III-V semiconductors, where micron-to-submicron-scale large-contrast refractive index change with an asymmetric face-centered cubic structure is formed by a method based on a wafer fusion and a very precise alignment technique.
Abstract: Three-dimensional photonic crystals operating at optical wavelength region are developed with III–V semiconductors, where micron-to-submicron-scale large-contrast refractive index change with an asymmetric face-centered cubic structure is formed by a method based on a wafer fusion and a very precise alignment technique. A considerable band-gap effect is successfully demonstrated in infrared-to-near-infrared wavelengths. It is pointed out for this method that the introduction of arbitrary defects states and/or efficient light emitters can be possible. For the example of the introduction of light-emitting element, a surface-emitting laser with a two-dimensional photonic crystal structure is developed, and very unique lasing characteristics are demonstrated. These results encourage us for the development of various quantum optical devices and circuits including not only passive but also active devices. Some ultra-small optical integrated circuits are proposed, and a guideline for the design of photonic crystal waveguides is successfully demonstrated.
TL;DR: In this paper, the electronic structures of Ga1−xMnxAs (x=0.063, 0.125) were investigated using the local density approximation (LDA) and LDA+U band calculations.
Abstract: Electronic structures of Ga1−xMnxAs (x=0.063, 0.125) are investigated using the local density approximation (LDA) and LDA+U band calculations. Both the LDA and LDA+U yield the half-metallic ground states for (Ga0.938Mn0.063)As, but only the LDA+U electronic structures are consistent with photoemission spectra. The states at the Fermi level are mainly of As 4p character, which mediates the RKKY-type magnetic intercation among Mn ions.
TL;DR: The VESUVIO project aims to provide unique prototype instrumentation at the ISIS-pulsed neutron source and to establish a routine experimental and theoretical program in neutron scattering spectroscopy at eV energies as discussed by the authors.
Abstract: The VESUVIO project aims to provide unique prototype instrumentation at the ISIS-pulsed neutron source and to establish a routine experimental and theoretical program in neutron scattering spectroscopy at eV energies. This instrumentation will be specifically designed for high momentum, , and energy transfer inelastic neutron scattering studies of microscopic dynamical processes in materials and will represent a unique facility for EU researchers. It will allow to derive single-particle kinetic energies and single-particle momentum distributions, n(p), providing additional and/or complementary information to other neutron inelastic spectroscopic techniques.
TL;DR: In this article, the morphology of the deposited gold islands and buried platinum clusters so obtained has been studied by grazing incidence small-angle X-ray scattering (GISAXS), coupled with a synchrotron radiation beam and two-dimensional detectors.
Abstract: Ion-beam sputtering deposition has been used to elaborate discontinuous gold and granular carbon–platinum thin films. The morphology of the deposited gold islands and buried platinum clusters so obtained has been studied by grazing incidence small-angle X-ray scattering (GISAXS). The full potentiality of this non-destructive technique at grazing incidence is obtained when it is coupled with a synchrotron radiation beam and two-dimensional detectors. The influence of argon ion-implantation performed during Au or C–Pt growth has been studied. A relevant information to understand and control the structural properties of such materials is then achieved.
TL;DR: In this article, a dynamic hysteresis model for electrical steel sheets is presented, which is a scalar model that links the exciting applied field on the sheet surface to the mean induction in the thickness of the sheet.
Abstract: A dynamic hysteresis model for thick electrical steel sheet is presented. It is a scalar model that links the exciting applied field on the sheet surface to the mean induction in the thickness of the sheet. The model is valid for any type of induction waveforms, even the very distorted ones that could be met in electrical motor. The model gives the excitation field H knowing the induction B. It results from the superposition of both static and dynamic hysteresis behaviour of the material. The static effect is represented by a set of reversal curves. The dynamic effect needs only six parameters to be completely identified and is expressed as a function of B and dB/dt. The relative error with respect to experiment is small and losses are estimated with a margin lower than 5%.
TL;DR: In this article, an itinerant type of ferromagnetic order, stable up to temperatures of the order of 600}900 K, is established for hexaborides with divalent cations.
Abstract: Various recent experimental investigations have revealed unusual magnetic properties of hexaborides with divalent cations M2‘. EuB 6 is ferromagnetic below 16 K and its low-temperature properties show remarkable similarities to those of manganese oxides, exhibiting the phenomenon of colossal magnetoresistance. Close to the phase transition as well as far below the ordering temperature, EuB 6 exhibits anomalous features, that are brie#y discussed. Alkaline-earth hexaborides are close to a metal}insulator transition and it has been found that, in a narrow range of electron doping, an itinerant-type of ferromagnetic order, stable up to temperatures of the order of 600}900 K, is established. This remarkable phenomenon is suspected to be due to the peculiar electronic band structure of these materials. ( 2000 Elsevier Science B.V. All rights reserved.
TL;DR: In this article, the magnetic properties of three differently prepared samples of the spinel ZnFe2O4 with μSR, neutron diffraction, Mossbauer effect and magnetization measurements were investigated.
Abstract: We have investigated the magnetic properties of three differently prepared samples of the spinel ZnFe2O4 with μSR, neutron diffraction, Mossbauer effect and magnetization measurements Below T N =105 K , the first sample (annealed) shows long-range antiferromagnetic order in coexistence with short-range magnetic order The second sample (rapidly quenched) shows only short-range magnetic order The third sample (nanostructured with an average particle size of about 9 nm) exhibits ferromagnetism below T c ≈460 K combined with superparamagnetism Below the blocking temperature of ∼50 K the nanostructured sample exhibits a dependence on applied magnetic fields similar to that observed in spin glass systems The roles of cation-site occupation and magnetic couplings in governing the different magnetic behaviors exhibited by the samples are discussed
TL;DR: In this article, the crystal field parameter (CFP) sets for rare earth (RE) ions doped at orthorhombic and/or lower symmetry sites were investigated.
Abstract: This work investigates the crystal-field parameter (CFP) sets for rare-earth (RE) ions doped at orthorhombic and/or lower symmetry, i.e. monoclinic or triclinic sites. Two important questions are addressed: (1) How do you compare CFP sets reported by different authors when there can be as many as six numerically different equivalent sets? and (2) How do you distinguish between global and local minima in the multi-parameter fittings? To answer the first question we propose to adopt the standardization of CFP sets. The orthorhombic and/or monoclinic standardization has been carried out for several illustrative CFP sets, including the contributions from various mechanisms, for NdF 3 , RE 2 Te 4 O 11 , and RE 3+ in garnet materials. It is shown that adopting a well-defined standardization convention enables meaningful comparison of CFP sets taken from various sources. The analysis of literature data reveals also cases when the CF parameters may be misinterpreted due to the choice of a different representation in the multi-parameter fittings. To answer the second question we propose the multiple correlated fitting technique (MCFT). Using experimental data for Nd 3+ in YAG and LaF 3 , MCFT is employed to probe for more reliable CFP sets.
TL;DR: An overview of recent developments and of the present status concerning low-energy μSR (LE-μSR) at the Paul Scherrer Institute is given in this article, where some schemes of possible future developments are discussed.
Abstract: An overview of recent developments and of the present status concerning low-energy μSR (LE-μSR) at the Paul Scherrer Institute is given. We also discuss some schemes of possible future developments, which are able to improve the potential of the LE-μSR method.
TL;DR: In this paper, the authors investigated optical properties of disordered one-dimensional (1D) binary photonic crystals and suggested the optimal design of broad band high reflectors to achieve high reflective properties.
Abstract: We investigated optical properties of disordered one-dimensional (1D) binary photonic crystals. With proper periodic structure on average, the disordered 1D photonic crystals display high reflective charateristics from visible to infrared, which is caused by the band-gap extension due to the combining effect of Bragg reflection and light localization. Optimal design of broad band high reflectors is also suggested.
TL;DR: In this paper, the authors investigated the dynamic properties of poly(dimethylsiloxane) (PDMS) and poly(vinyl acetate) (PVAc) filled with hydrophilic Aerosil (nano-particles of fumed silica) using the backscattering spectrometer IRIS at ISIS.
Abstract: We have investigated the dynamic properties of poly(dimethylsiloxane) (PDMS) and poly(vinyl acetate) (PVAc) filled with hydrophilic Aerosil (nano-particles of fumed silica) using the backscattering spectrometer IRIS at ISIS. Through the analysis of the incoherent scattering, the quasi-elastic neutron scattering (QENS) technique probes the motion of the hydrogen atoms and it therefore provides detailed information on the reduced mobility of chain segments in polymer filler systems. QENS measurements reveal a progressive slowing down of the motion with increasing particle surface area which is in agreement with the DMTA data of Tsagaropoulos and Eisenberg. In particular, the QENS spectra of the polymer-filler composites confirmed the existence of two dynamic processes. Therefore, data analysis was carried out by taking into account two contributions: (a) a quasielastic component due to chains not affected by the presence of fillers and (b) an elastic component from chains whose dynamics is strongly restricted. The latter depends on the specific surface area of the particles and their weight fraction in the composites.
TL;DR: In this paper, the authors show that substantial quantum squeezing of mechanical motion can be achieved for micron-sized cantilever devices using available techniques, and they also show that this can be done in a single-stage manner.
Abstract: We show that substantial quantum squeezing of mechanical motion can be achieved for micron-sized cantilever devices using available techniques.
TL;DR: In this paper, the concept of the normal metal hot-electron microbolometer with capacitive coupling of an absorber to the antenna (NHEB-CC) is proposed.
Abstract: A novel concept of the normal metal hot-electron microbolometer with capacitive coupling of an absorber to the antenna (NHEB-CC) is proposed. Tunnel junctions can be used for high-frequency capacitive coupling giving perfect isolation of hot electrons in the small volume of the absorber. This concept represents a further development of the basic idea of an antenna-coupled bolometer, used in the realization of normal-metal hot-electron microbolometers with Andreev mirrors (NHEB-A). The NHEB-CC technology with capacitive isolation of the absorber avoids the likely problems of frequency limitation for frequencies with an energy quantum ℏ ω higher than the superconducting gap Δ and brings other advantages in comparison with NHEB-A system.
TL;DR: In this article, the morphology of dewetted thin polymer-blend films of deuterated polystyrene and polyparamethylstyrene on top of silicon surfaces is investigated.
Abstract: The morphology of dewetted thin polymer-blend films of deuterated polystyrene (dPS) and polyparamethylstyrene (PpMS) on top of silicon surfaces is investigated. The film thickness of the originally homogeneous films is varied between 19 and 104 A. Compared to the radius of gyration of the unperturbed molecule, R g =106 A , the as-prepared films are confined in the direction perpendicular to the sample surface. The dewetting results from the storage of the samples under toluene vapor atmosphere. Atomic force microscopy (AFM) and grazing incidence small-angle scattering (GISAS) are used. From the differences in the GISAS data measured with X-rays compared to data measured with neutrons a random distribution of the molecules inside the individual droplets is determined. Thus from dewetting under toluene atmosphere no periodicity in the internal structure exists. The, within all methods derived, most prominent in-plane length corresponds to the mean droplet distance. Its function of film thickness is explainable by the spinodal dewetting model.
TL;DR: In this paper, the authors performed ZF-μSR measurements of Sr2RuO4 and have observed a spontaneous magnetic field below Tc, which is consistent with a superconducting gap with no nodes as expected for the E u (k x ± i k y ) state.
Abstract: We have performed ZF-μSR measurements of Sr2RuO4 and have observed a spontaneous magnetic field below Tc. This observation, combined with other symmetry considerations demonstrates that superconductivity in Sr2RuO4 is of ‘p-wave’ (odd-parity) type. Our transverse field μSR measurements in the mixed state with B=150 G || c clearly indicate the presence of a square flux lattice. We have analysed the field distribution in terms of the penetration depth, coherence length and a Fermi surface anisotropy term and found λ(T=0)=1900 A. λ(T→0) is quite flat, consistent with a superconducting gap with no nodes as expected for the E u (k x ± i k y ) state.
TL;DR: In this article, the formation of intermediate layers was investigated in Mo/Si multilayers produced by e-beam evaporation and ion-beam smoothening, and a model of a four-layer step profile structure of the multilayer period was applied successfully to account for grazing incidence X-ray reflectivity of the structures.
Abstract: The formation of intermediate layers was investigated in Mo/Si multilayers produced by e-beam evaporation and ion-beam smoothening. A model of a four-layer step profile structure of the multilayer period was applied successfully to account for grazing incidence X-ray reflectivity of the structures. We have used a special method to determine the multilayer period composition, namely the use of a laterally graded multilayer of which only the thickness of the spacer layer was varied. The well-known modulation of the Bragg peak intensities of 0.154 nm X-rays was then used to determine the thickness and the composition of the silicides formed at the boundaries. The impact of the polishing conditions on the thickness and composition of the intermediate layers was investigated. The study allowed optimization of the composition of Mo/Si multilayer for use at near-normal incidence in the 12.5–15 nm wavelength area for Extreme UV Lithography.
TL;DR: In this paper, the electrical resistivity behavior of the compounds La 0.67 Ca 0.33 Mn 1− x Cr x O 3 (x = 0.00, 0.60) was studied by X-ray diffraction (XRD), AC and DC magnetization, and DC electrical resistivities measurement techniques, and Ferromagnetism is observed up to as high as 60% of Cr substitution.
Abstract: The compounds La 0.67 Ca 0.33 Mn 1− x Cr x O 3 ( x =0.00, 0.05, 0.10, 0.15, 0.20, 0.35, 0.50 and 0.60) have been studied by X-ray diffraction (XRD), AC and DC magnetization, and DC electrical resistivity measurement techniques. Ferromagnetism is observed up to as high as 60% of Cr substitution. Electrical resistivity behavior of the compounds as a function of temperature could be explained on the basis of adiabatic small polaron model.
TL;DR: In this article, the authors made 59 Co NMR measurements up to 800 K to clarify the spin state and the metal-insulator (MI) transition in LaCoO3 and RCoO-3 (R=Nd, Sm and Eu).
Abstract: We made 59 Co NMR measurements up to 800 K to clarify the spin state and the metal–insulator (MI) transition in LaCoO3 and RCoO3 (R=Nd, Sm and Eu). The 59 Co Knight shift 59 K in LaCoO3 has a peak due to the spin state transition from the low-spin to intermediate-spin states at ∼100 K. However, 59 K in RCoO3 is almost independent of temperature up to the temperature TMI∼600 K where the MI transition takes place. This means that the spin state in RCoO3 remains the low-spin state up to TMI.
TL;DR: In this paper, the authors found that the pronounced three-dimensional nature of the electrodes results in an extremely high sensitivity of the field emission resonance spectra to the fine details of the surface geometry, electronic structure and electric field distribution at small electrode separations.
Abstract: The additional information provided by field emission resonance spectra significantly increases the potential of the mechanically controllable break junction technique. We have found that the pronounced three-dimensional nature of the electrodes results in an extremely high sensitivity of the field emission resonance spectra to the fine details of the surface geometry, electronic structure and electric field distribution at small electrode separations. At larger distances a quasiclassical approximation can be used for the determination of the metal work function, precise calibration of the electrode relative displacement and discrimination between “blunt” and “sharp” electrodes on the basis of the distance–voltage z ( V ) dependence.