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Magnetic structure of ErNi2B2C
No full textThis article is published as Zarestky, J., C. Stassis, A. I. Goldman, P. C. Canfield, P. Dervenagas, B. K. Cho, and D. C. Johnston. "Magnetic structure of ErNi 2 B 2 C." Physical Review B 51, no. 1 (1995): 678.
DOI: 10.1103/PhysRevB.51.678.
Copyright 1995 American Physical Society.
Posted with permission
Neutron scattering studies of RENi2B2C (RE=Lu,Y,Ho,Er): Lattice dynamics
No full textInelastic neutron scattering techniques have been used to study the low energy phonon excitations in superconducting RENi2B2C (RE=Lu, Y) to further characterize the anomalous features observed by Kawano et al. (Phys. Rev. Lett., 77, 4628 (1996)) for RE=Y and Stassis et al. (Phys. Rev. B, 55, R8678 (1997)) for RE=Lu, when these systems enter the superconducting ground state. We find that above T c the frequencies of the [delta]4[[xi] 00] lowest-lying acoustic and optic phonon modes decrease with decreasing temperature, for [xi] close to the nesting vector [xi]m. In addition there is a shift of intensity from the upper to the lower mode, an effect characteristic of mode coupling. At temperatures below approximately 100K only a single unresolved peak is observed. The observed anticrossing behavior of these modes above T c can be described satisfactorily in both compounds by a coupled-mode model. Below T c the observed spectrum changes dramatically: it consists of a sharp peak at approximately 4 meV with a broad weak shoulder at higher energies. The experimental results unambiguously show that this dramatic change is due to the onset of superconductivity in these compounds. In this temperature region, the results are in qualitative agreement with recent theoretical calculations.</p
Incommensurate antiferromagnetism in the intermetallic superconductor HoNi2B2C
No full textWe report high-resolution x-ray and neutron-scattering studies of the antiferromagnetism of the rare-earth superconductor, HoNi2B2C (T-C=8.5 K). At low temperatures, T<5 K, the superconductivity coexists with a long-range ordered, commensurate Neel state. In the incommensurate antiferromagnetic state, 5 K5 K, are interpreted in terms of local strains.This article is published as Hill, J. P., B. J. Sternlieb, D. Gibbs, C. Detlefs, A. I. Goldman, C. Stassis, P. C. Canfield, and B. K. Cho. "Incommensurate antiferromagnetism in the intermetallic superconductor HoNi 2 B 2 C." Physical Review B 53, no. 6 (1996): 3487.
DOI: 10.1103/PhysRevB.53.3487.
Copyright 1996 American Physical Society.
Posted with permission
Determination of magnetic-moment directions using x-ray resonant exchange scattering
No full textWe present determinations of the magnetic structures of NCdNi2B2C and SmN2B2C by means of x-ray resonant exchange scattering (XRES). The integrated intensity of a number of magnetic reflections was measured as a function of the Bragg angle and compared to model calculations for various magnetic structures. The two compounds were found to have the same magnetic modulation wave vector but different moment directions. A resonant feature observed below the Sm L(3)-absorption edge, similar to unexplained effects found in other light rare-earth compounds, is identified as quadrupolar XRES and is used to refine the details of the moment direction.This article is published as Detlefs, Carsten, A. H. M. Z. Islam, A. I. Goldman, C. Stassis, P. C. Canfield, J. P. Hill, and D. Gibbs. "Determination of magnetic-moment directions using x-ray resonant exchange scattering." Physical Review B 55, no. 2 (1997): R680.
DOI: 10.1103/PhysRevB.55.R680.
Copyright 1997 American Physical Society.
Posted with permission
Single crystal neutron diffraction study of the magnetic structure of TmNi2B2C
No full textNeutron diffraction techniques have been used to study the magnetic structure of single crystals of the magnetic superconductor (Tc≅11 K) TmNi2B2C. We find that below approximately 1.5 K the magnetic moments order in an incommensurate spin wave with propagation vector qm=qm(a*+b*) [or qm=qm(a*−b*)] with qm=0.094±0.001. The spin wave is transverse with the moments aligned along the c axis, and the observation of relatively intense higher-order harmonics shows that the modulation is not purely sinusoidal but considerably squared. This incommensurate magnetic structure, which coexists with superconductivity below TN≅1.5 K, is quite different from those observed in the magnetic superconductors HoNi2B2C and ErNi2B2C. The origin of diffraction peaks observed in scans parallel to a* is briefly discussed.This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Sternlieb, B., C. Stassis, A. I. Goldman, P. Canfield, and S. Shapiro. "Single crystal neutron diffraction study of the magnetic structure of TmNi2B2C." Journal of applied physics 81, no. 8 (1997): 4937-4939, and may be found at DOI: 10.1063/1.365003. Copyright 1997 American Institute of Physics. Posted with permission
Low-energy phonon excitations in superconducting RNiB2C (R = Lu, Y)
No full textInelastic neutron-scattering techniques have been used to study the low-energy phonon excitations in superconducting RNi2B2C (R = Lu, Y) to further characterize the anomalous features observed by Kawano et al. [Phys. Rev. Lett. 77, 4628 (1996)] for R = Y and Stassis et al. [Phys. Rev. B 55, R8678 (1997)] for R = Lu, when these systems enter the superconducting ground state. We find that above T, the frequencies of the Delta(4)[xi 00] lowest-lying acoustic and optic phonon modes decrease with decreasing temperature, for xi close to the nesting vector xi(m). In addition there is a shift of intensity from the upper to the lower mode, an effect characteristic of mode coupling. The observed intensity transfer between these modes above T-c can be described satisfactorily in both compounds by a coupled-mode model. Below T-c the observed spectrum changes dramatically: it consists of a sharp peak at approximately 4 meV with a broad weak shoulder at higher energies. The experimental results unambiguously show that this dramatic change is due to the onset of superconductivity in these compounds. In this temperature region, the results are in qualitative agreement with recent theoretical calculations.This article is published as Bullock, M., J. Zarestky, C. Stassis, A. Goldman, P. Canfield, Zentaro Honda, Gen Shirane, and S. M. Shapiro. "Low-energy phonon excitations in superconducting R Ni 2 B 2 C (R= Lu, Y)." Physical Review B 57, no. 13 (1998): 7916.
DOI: 10.1103/PhysRevB.57.7916.
Copyright 1998 American Physical Society.
Posted with permission
Magnetoelastic tetragonal-to-orthorhombic distortion in ErNi2B2C
No full textWe have performed synchrotron x-ray scattering experiments on single crystals of ErNi2B2C. Below 6.3 K, the (2,0,0) Bragg peak splits, indicating a tetragonal-to-orthorhombic distortion. The mismatch between the a and b lattice parameters appears coincident with the onset of long-range antiferromagnetic order and increases continuously with decreasing temperature, reaching a value of a/b-1 approximate to 0.2% at 3.7 K.This article is published as Detlefs, C., A. H. M. Z. Islam, T. Gu, A. I. Goldman, C. Stassis, P. C. Canfield, J. P. Hill, and T. Vogt. "Magnetoelastic tetragonal-to-orthorhombic distortion in ErNi 2 B 2 C." Physical Review B 56, no. 13 (1997): 7843.
DOI: 10.1103/PhysRevB.56.7843.
Copyright 1997 American Physical Society.
Posted with permission
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Magnetic pair breaking in HoNi2B2C
No full textNeutron-diffraction techniques have been used to study the interplay between superconductivity and magnetism in HoNi2B2C (Tc=8 K). The experimental results, obtained on single crystals, show that below approximately 4.7 K, this compound is in a simple antiferromagnetic state that coexists with superconductivity. Between approximately 4.7 and 6 K, an incommensurate modulated magnetic structure has been found. This observation strongly suggests that pair breaking associated with this incommensurate magnetic structure is responsible for the deep minimum in Hc2 and the near-reentrant behavior observed in this compound at approximately 5 K.This article is published as Goldman, A. I., C. Stassis, P. C. Canfield, J. Zarestky, P. Dervenagas, B. K. Cho, D. C. Johnston, and B. Sternlieb. "Magnetic pair breaking in HoNi 2 B 2 C." Physical Review B 50, no. 13 (1994): 9668. DOI: 10.1103/PhysRevB.50.9668. Posted with permission.</p
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