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  • 1995-1999  (8)
  • 1990-1994  (11)
  • 1
    Electronic Resource
    Electronic Resource
    Magnetic ordering in pyrochlore Ho2Mn2O7 : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 6173-6175 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The magnetic susceptibility of Ho2Mn2O7 with a spontaneous rise below about 40 K and a paramagnetic Curie temperature of +39 K suggests a ferromagnetic ordering. Indeed neutron diffraction profiles show strongly enhanced Bragg peaks with a temperature dependence which indicates an apparent Tc≈35 K. Nonetheless, the magnetic diffraction pattern is not consistent with a collinear ferro or ferrimagnetic ordering of the Ho3+ and Mn4+ sublattices. Furthermore, specific heat and small angle neutron scattering (SANS) show features which are also incompatible with conventional long-range order. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.362063
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  • 2
    Electronic Resource
    Electronic Resource
    Small-angle neutron scattering behavior of Fe91Zr9 glass under magnetic field : The 40th annual conference on magnetism and magnetic materials (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 5146-5148 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Zero-field and in-field small-angle neutron scattering measurements over a wide Q range are presented for the Fe91Zr9 metallic glass in the 10–290 K range. Two transitions observed at 210 K and around 60 K are related to Tc and reentrant transition temperature, respectively. The spectra (0.003 A(ring)−1〈Q〈0.5 A(ring)−1) reveal the existence of an important contribution at the lowest Q values and at least two humps in the entire curves. The application of the magnetic field results in an anisotropic signal, and a global decrease of intensity. The magnetic field drastically reduces I(Q) in the region for Q〈0.04 A(ring)−1, but not so strongly at larger Q values (even at H=4 T), becoming more evident a remaining hump. Its origin can so far be uniquely explained by the models dealing with the existence of clusters embedded in a ferromagnetic matrix. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.361918
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  • 3
    Electronic Resource
    Electronic Resource
    Neutron diffraction from the vortex lattice in the heavy fermion superconductor UPt3 (invited) (abstract) : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 6788-6788 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The heavy fermion superconductor UPt3 is thought to have a d-wave pairing ground state. The principal experimental evidence for this consists of the anisotropy of the power-law behavior observed in transverse ultrasound and μ+ SR measurements. The observation of a complex phase diagram in the superconducting state in ultrasound, torsional oscillator, and specific heat measurements may be a further indication of an unconventional pairing state. Theoretical investigations suggest the possibility of vortex lattices that are unconventional in their symmetry, their quantization, or the structure of their composite vortex cores. Transitions between such exotic vortex lattices are in principle allowed and could explain the observed features at H≈0.6 Hc2 (for H(parallel)cˆ) and H≈0.3Hc2 (for H⊥cˆ). Neutron diffraction is an ideal bulk probe of the microscopic properties of the vortex lattice. We have studied the vortex lattice with H⊥cˆ and T≈50 mK in the field range 0.75〈H〈10 kG. The structure of the vortex lattice and the quantization of the vortices, in addition to the London penetration depth, λL, the coherence length, ξ, and the effective mass anisotropy are all well determined by our measurements. The lattice is oblique hexagonal with conventional quantization. Its anisotropy can be explained by considering a combination of Fermi surface and gap anisotropy. However, the lattice does not appear to change near the transition between superconducting phases identified by other techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358129
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  • 4
    Electronic Resource
    Electronic Resource
    Small-Angle X-ray and Neutron Scattering from Bulk and Oriented Triblock Copolymer Gels (1995)
    s.l. : American Chemical Society
    Macromolecules 28 (1995), S. 2054-2062 
    Details
    ISSN: 1520-5835
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/ma00110a045
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  • 5
    Electronic Resource
    Electronic Resource
    Resolution function and flux at the sample for small-angle X-ray scattering calculated in position–angle–wavelength space (1991)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 24 (1991), S. 893-909 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A method for calculating the flux at the sample position and the resolution function based on the general description of synchrotron X-ray beamlines in position–angle–wavelength space has been developed. A mathematical formulation is presented, in which source, transmission function for the slits and acceptance windows of the monochromator crystals are approximated by Gaussian functions. These approximations allow all of the algebra in connection with combining the different contributions to be done analytically. When the beam passes the various components of the beamline, such as flight paths, monochromators and mirrors, it results in coordinate transformations in parameter space. By inserting the transformations in the intensity distribution of the source, transmission functions of the slits and acceptance windows of the monochromators, these are transformed to the position of the sample. Their product gives the intensity distribution at this position and from this the resolution function in reciprocal space is calculated. The resolution of the detector is easily included by a convolution. The transmissions of the slits and the acceptance windows of the monochromator crystals have been normalized to give the same integrated transmission and reflectivities as the functions they approximate. Therefore the flux at the sample position can be calculated by multiplication of the brilliance of the source and the result obtained from an integration of the distribution over the two position parameters, the two angle parameters and the wavelength. The theory has been applied to an example and gives reasonable results for sample intensity and resolution function.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891003692
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  • 6
    Electronic Resource
    Electronic Resource
    Model-independent determination of the surface scattering-length-density profile from specular reflectivity data (1992)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 25 (1992), S. 129-145 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: An approach for analysing neutron and X-ray specular reflectivity data from stratified media having variation in the scattering-length density near the surface is described. The method has its origin in small-angle scattering and it is composed of two steps: (i) indirect Fourier transformation [Glatter (1977). J. Appl. Cryst. 10, 415–421] giving the profile correlation function p(z) of the derivative dρ/dz of the scattering-length density; (ii) square-root deconvolution [Glatter (1981). J. Appl. Cryst. 14, 101–108] giving dρ/dz and ρ, the scattering-length-density profile. The only requirement for applying the method is that the scattering-length density varies only in a limited range. In nearly all cases the approach does not require any knowledge of the chemical composition of the surface layer and consequently incorporates a certain degree of objectivity. The method gives the smoothest profile which agrees with the experimental reflectivity data. The method is tested on simulated reflectivity data for a series of different surface profiles and subsequently used for analysing experimental data on fluorocarbon amphiphiles in water and salt solutions. The tests on simulated data show that the indirect Fourier transformation gives correlation functions agreeing very well with the corresponding functions of the original profiles. It is further demonstrated that the square-root deconvolution gives reliable results for the scattering-length-density profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889891010907
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  • 7
    Electronic Resource
    Electronic Resource
    Propagating errors in small-angle scattering data treatment (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 241-248 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: The problem of error propagation using indirect methods for small-angle scattering data treatment is considered. In these methods, the number of parameters to be determined is normally larger than the maximum number of independent parameters predicted by the Shannon sampling theorem and the solution has to be regularized. It is shown in model examples that evaluation of the error propagation via the covariance matrix can lead to significant overestimation of the propagated errors. The reason is that the procedure involves inversion of an ill-conditioned matrix. As an alternative, the Monte Carlo simulation procedure is recommended.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889893008337
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  • 8
    Electronic Resource
    Electronic Resource
    Optimum intensity in small-angle neutron scattering. An experimental comparison between symmetric and asymmetric geometries (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 330-337 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Results of an experimental comparison of the performance of symmetric (with the flight path between source and sample, L1, equal to the flight path between sample and detector, L2) and asymmetric (L1 ≠ L2) geometries of a small-angle neutron scattering instrument are reported. The comparison was performed under the assumption that a specific range of scattering vectors is required to be measured with a certain resolution. The measurements were performed at the spectrometer installed at the Risø National Laboratory, using as test samples a crystalline powder, a single-crystal and a sample that produces a smooth scattering curve at small angles. The results obtained show that, when a specific scattering-vector range has to be measured with a specific resolution, the optimized asymmetric spectrometer performs better than the symmetric instrument. A simple graphical approach for the determination of the best geometry to perform a given measurement is introduced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S002188989301043X
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  • 9
    Electronic Resource
    Electronic Resource
    Determination of size distribution from small-angle scattering data for systems with effective hard-sphere interactions (1994)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 27 (1994), S. 595-608 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Methods for the free-form determination of size distributions for systems with hard-sphere interactions are described. An approximation, called the local monodisperse approximation, is introduced. Model calculations show that this approximation gives relatively small errors even at relatively high polydispersities and large volume fractions. The size distributions are determined by least-squares methods with smoothness and non-negativity constraints. The local monodisperse approximation leads to normal equations that are linear in the amplitude of the size distribution. This is used when solving the least-squares problem: only the two effective parameters describing the interference effects are treated as nonlinear parameters in an external optimization routine. The parameters describing the size distribution are determined by a linear least-squares method. The size distribution is also determined using the nonlinear equations from the calculation of the scattering intensity in the Percus–Yevick approximation. For this, a nonlinear least-squares routine with a smoothness constraint and a non-negativity constraint is used. Both approaches are tested by analysis of simulated examples calculated by the analytical expressions in the Percus–Yevick approximation. Finally, the methods are applied to two sets of experimental data from silica particles and from δ′ precipitates in an Al–Li alloy. For the simulated examples, good agreement is found with the input distributions. For the experimental examples, the results agree with the expected and known properties of the samples.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889893013810
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  • 10
    Electronic Resource
    Electronic Resource
    Instrumental Smearing Effects in Radially Symmetric Small-Angle Neutron Scattering by Numerical and Analytical Methods (1995)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 28 (1995), S. 105-114 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: A numerical calculation method for determining the resolution functions for radially symmetric collimation and scattering is described. In the present approach, the total number of integrations is reduced to four by use of the radial symmetry of the geometry. Furthermore, the beam-stop shadowing effect is included exactly. A typical calculation can be completed in minutes on current personal computers. An interactive computer program allows the user to enter the experimental parameters such as aperture size and wavelength spread, allowing smearing calculations to be handled routinely as a `black box' operation. The exact smearing treatment is compared both to an improved technique involving Gaussian resolution functions where corrections for the beam stop are included and to results from Monte Carlo simulations. In most experiments, the use of a Gaussian distribution to approximate the resolution is preferred on account of its ease of calculation. But in a few cases, such as Porod scattering, the present more extensive numerical calculation or inclusion of the developed beam-stop-shadowing correction factors into a Gaussian scheme are needed for an adequate prediction of the smearing effects.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889894010095
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