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A Mean Field Model for the Quadrupolar Phases of UPd$_3$
Authors:
Manh Duc Le,
Keith A. McEwen,
Martin Rotter,
Mathias Doerr,
Alexander Barcza,
Je-Geun Park,
James Brooks,
Eric Jobiliong,
David Fort
Abstract:
UPd$_3$ is known to exhibit four antiferroquadrupolar ordered phases at low temperatures. We report measurements of the magnetisation and magnetostriction of single crystal UPd$_3$, along the principal symmetry directions, in fields up to 33 T. These results have been combined with recent inelastic neutron and x-ray resonant scattering measurements to construct a mean field model of UPd$_3$ includ…
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UPd$_3$ is known to exhibit four antiferroquadrupolar ordered phases at low temperatures. We report measurements of the magnetisation and magnetostriction of single crystal UPd$_3$, along the principal symmetry directions, in fields up to 33 T. These results have been combined with recent inelastic neutron and x-ray resonant scattering measurements to construct a mean field model of UPd$_3$ including up to fourth nearest neighbour interactions. In particular we find that anisotropic quadrupolar interactions must be included in order to explain the low temperature structures derived from the scattering data.
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Submitted 19 March, 2014;
originally announced March 2014.
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E1 and E2 contributions to the L3 resonance line shape in antiferromagnetic holmium
Authors:
L Bouchenoire,
A Mirone,
S D Brown,
P Strange,
T Wood,
P Thompson,
D Fort,
J Fernandez-Rodriguez
Abstract:
A detailed study of the angular, energy and polarization dependences of the electric dipolar (E1: 2p->5d) and quadrupolar (E2: 2p->4f) contributions to the x-ray scattering cross-section is presented for holmium in its basal plane spiral antiferromagnetic phase at the L3 edge. The corresponding E1 and E2 scattering factors have been extracted from fits to the experimental energy line shapes taki…
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A detailed study of the angular, energy and polarization dependences of the electric dipolar (E1: 2p->5d) and quadrupolar (E2: 2p->4f) contributions to the x-ray scattering cross-section is presented for holmium in its basal plane spiral antiferromagnetic phase at the L3 edge. The corresponding E1 and E2 scattering factors have been extracted from fits to the experimental energy line shapes taking into account for the first time a split dipole resonance. Using the imaginary part of the resonant scattering factors to retrieve the XMCD spectrum, we find qualitative agreement with the dichroic spectrum measured in transmission through a holmium foil.
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Submitted 18 August, 2009;
originally announced August 2009.
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Morphology of the Superconducting Vortex Lattice in Ultra-Pure Niobium
Authors:
S. Mühlbauer,
C. Pfleiderer,
P. Böni,
M. Laver,
E. M. Forgan,
D. Fort,
U. Keiderling,
G. Behr
Abstract:
The morphology of the superconducting flux line lattice (FLL) of Nb comprises gradual variations with various lock-in transitions and symmetry breaking rotations. We report a comprehensive small-angle neutron scattering study of the FLL in an ultra-pure single crystal of Nb as a function of the orientation of the applied magnetic field. We attribute the general morphology of the FLL and its orie…
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The morphology of the superconducting flux line lattice (FLL) of Nb comprises gradual variations with various lock-in transitions and symmetry breaking rotations. We report a comprehensive small-angle neutron scattering study of the FLL in an ultra-pure single crystal of Nb as a function of the orientation of the applied magnetic field. We attribute the general morphology of the FLL and its orientation to three dominant mechanisms. First, non-local contributions, second, the transition between open and closed Fermi surface sheets and, third, the intermediate mixed state between the Meissner and the Shubnikov phase.
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Submitted 20 February, 2009;
originally announced February 2009.
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Dipolar excitations at the LIII x-ray absorption edges of the heavy rare earth metals
Authors:
S. D. Brown,
P. Strange,
L. Bouchenoire,
B. Zarychta,
P. B. J. Thompson,
D. Mannix,
S. J. Stockton,
M. Horne,
E. Arola,
H. Ebert,
Z. Szotek,
W. M. Temmerman,
D. Fort
Abstract:
We report measured dipolar asymmetry ratios at the LIII edges of the heavy rare earth metals. The results are compared with a first principles calculation and excellent agreement is found. A simple model of the scattering is developed, enabling us to re-interpret the resonant x-ray scattering in these materials and to identify the peaks in the asymmetry ratios with features in the spin and orbit…
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We report measured dipolar asymmetry ratios at the LIII edges of the heavy rare earth metals. The results are compared with a first principles calculation and excellent agreement is found. A simple model of the scattering is developed, enabling us to re-interpret the resonant x-ray scattering in these materials and to identify the peaks in the asymmetry ratios with features in the spin and orbital moment densities.
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Submitted 19 November, 2007;
originally announced November 2007.
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Determination of the Antiferroquadrupolar Order Parameters in UPd3
Authors:
H. C. Walker,
K. A. McEwen,
D. F. McMorrow,
S. B. Wilkins,
F. Wastin,
E. Colineau,
D. Fort
Abstract:
By combining accurate heat capacity and X-ray resonant scattering results we have resolved the long standing question regarding the nature of the quadrupolar ordered phases in UPd_3. The order parameter of the highest temperature quadrupolar phase has been uniquely determined to be antiphase Q_{zx} in contrast to the previous conjecture of Q_{x^2-y^2} . The azimuthal dependence of the X-ray scat…
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By combining accurate heat capacity and X-ray resonant scattering results we have resolved the long standing question regarding the nature of the quadrupolar ordered phases in UPd_3. The order parameter of the highest temperature quadrupolar phase has been uniquely determined to be antiphase Q_{zx} in contrast to the previous conjecture of Q_{x^2-y^2} . The azimuthal dependence of the X-ray scattering intensity from the quadrupolar superlattice reflections indicates that the lower temperature phases are described by a superposition of order parameters. The heat capacity features associated with each of the phase transitions characterize their order, which imposes restrictions on the matrix elements of the quadrupolar operators.
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Submitted 26 October, 2006;
originally announced October 2006.
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Observation of a strongly nested Fermi surface in the shape-memory alloy Ni[0.62]Al[0.38]
Authors:
S. B. Dugdale,
R. J. Watts,
J. Laverock,
Zs. Major,
M. A. Alam,
M. Samsel-Czekala,
G. Kontrym-Sznajd,
Y. Sakurai,
M. Itou,
D. Fort
Abstract:
The Fermi surface topology of the shape-memory alloy Ni[0.62]Al[0.38] has been determined using Compton scattering. A large area of this Fermi surface can be made to nest with other areas by translation through a vector of ~ 0.18 [1,1,0] (2pi/a), which correponds to the wavevector associated with martensitic precursor phenomena such as phonon softening and diffuse streaking in electron diffracti…
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The Fermi surface topology of the shape-memory alloy Ni[0.62]Al[0.38] has been determined using Compton scattering. A large area of this Fermi surface can be made to nest with other areas by translation through a vector of ~ 0.18 [1,1,0] (2pi/a), which correponds to the wavevector associated with martensitic precursor phenomena such as phonon softening and diffuse streaking in electron diffraction patterns. This observation is compelling evidence that these phenomena are driven by the enhanced electron-lattice coupling due to the Fermi surface nesting.
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Submitted 1 February, 2006;
originally announced February 2006.
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Thermal Expansion and Magnetostriction Studies of a Kondo Lattice Compound: Ceagsb2
Authors:
D. T. Adroja,
P. C. Riedi,
J. G. M. Armitage,
D. Fort
Abstract:
We have investigated a single crystal of CeAgSb2 using low field ac-susceptibility, thermal expansion and magnetostriction measurements in the temperature range 1.5K to 90K. The ac-susceptibility exhibits a sharp peak at 9.7K for both B//c and B perp c due to the magnetic ordering of the Ce moment. The thermal expansion coefficient alpha, exhibits highly anisotropic behaviour between 3K and 80K…
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We have investigated a single crystal of CeAgSb2 using low field ac-susceptibility, thermal expansion and magnetostriction measurements in the temperature range 1.5K to 90K. The ac-susceptibility exhibits a sharp peak at 9.7K for both B//c and B perp c due to the magnetic ordering of the Ce moment. The thermal expansion coefficient alpha, exhibits highly anisotropic behaviour between 3K and 80K : alpha is positive for dL/L perp c, but negative for dL/L // c. Furthermore, alpha (for dL/L) perp c (i.e. in ab-plane) exhibits a sharp peak at TN followed by a broad maximum at 20K, while a sharp negative peak at TN followed by a minimum at 20K has been observed for (dL/L //) the c direction. The observed maximum and minimum in alpha(T) at 20K have been attributed to the crystalline field effect on the J=5/2 state of the Ce3+ ion. The magnetostriction also exhibits anisotropic behaviour with a large magnetostriction along the c-axis. The ab-plane magnetostriction exhibits a peak at B=3.3T at 3K, which is consistent with the observed peak in the magnetoresistance measurements.
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Submitted 26 June, 2002;
originally announced June 2002.