29 research outputs found
A Mean Field Model for the Quadrupolar Phases of UPd
UPd is known to exhibit four antiferroquadrupolar ordered phases at low
temperatures. We report measurements of the magnetisation and magnetostriction
of single crystal UPd, 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 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.Comment: 9 pages, 6 figures, 3 table
Ontology Based Integration of Distributed and Heterogeneous Data Sources in ACGT.
In this work, we describe the set of tools comprising the Data Access Infrastructure within Advancing Clinic-genomic Trials on Cancer (ACGT), a R&D Project funded in part by the European. This infrastructure aims at improving Post-genomic clinical trials by providing seamless access to integrated clinical, genetic, and image databases. A data access layer, based on OGSA-DAI, has been developed in order to cope with syntactic heterogeneities in databases. The semantic problems present in data sources with different nature are tackled by two core tools, namely the Semantic Mediator and the Master Ontology on Cancer. The ontology is used as a common framework for semantics, modeling the domain and acting as giving support to homogenization. SPARQL has been selected as query language for the Data Access Services and the Mediator. Two experiments have been carried out in order to test the suitability of the selected approach, integrating clinical and DICOM image databases
Comment on 'Nonreciprocal light propagation in a silicon photonic circuit'
We show that the structure demonstrated by Feng et al. (Reports, 5 August 2011, p. 729) cannot enable optical isolation because it possesses a symmetric scattering matrix. Moreover, one cannot construct an optical isolator by incorporating this structure into any system as long as the system is linear and time-independent and is described by materials with a scalar dielectric function
Rich Magnetic Phase Diagram of Putative Helimagnet SrFeO
The cubic perovskite SrFeO was recently reported to host hedgehog- and
skyrmion-lattice phases in a highly symmetric crystal structure which does not
support the Dzyaloshinskii-Moriya interactions commonly invoked to explain such
magnetic order. Hints of a complex magnetic phase diagram have also recently
been found in powder samples of the single-layer Ruddlesden-Popper analog
SrFeO, so a reinvestigation of the bilayer material SrFeO,
believed to be a simple helimagnet, is called for. Our magnetization and
dilatometry studies reveal a rich magnetic phase diagram with at least 6
distinct magnetically ordered phases and strong similarities to that of
SrFeO. In particular, at least one phase is apparently
multiple-, and the s are not observed to vary among the
phases. Since SrFeO has only two possible orientations for its
propagation vector, some of the phases are likely exotic multiple-
order, and it is possible to fully detwin all phases and more readily access
their exotic physics.Comment: 14 pages, 13 figure
High resolution magnetostriction measurements in pulsed magnetic fields using fiber Bragg gratings
Stripe-yz magnetic order in the triangular-lattice antiferromagnet KCeS2
Yb- and Ce-based delafossites were recently identified as effective spin-1/2 antiferromagnets on the triangular lattice. Several Yb-based systems, such as NaYbO2, NaYbS2, and NaYbSe2, exhibit no long-range order down to the lowest measured temperatures and therefore serve as putative candidates for the realization of a quantum spin liquid. However, their isostructural Ce-based counterpart KCeS2 exhibits magnetic order below TN = 400 mK, which was so far identified only in thermodynamic measurements. Here we reveal the magnetic structure of this long-range ordered phase using magnetic neutron diffraction. We show that it represents the so-called 'stripe-yz' type of antiferromagnetic order with spins lying approximately in the triangular-lattice planes orthogonal to the nearest-neighbor Ce–Ce bonds. No structural lattice distortions are revealed below TN, indicating that the triangular lattice of Ce3+ ions remains geometrically perfect down to the lowest temperatures. We propose an effective Hamiltonian for KCeS2, based on a fit to the results of ab initio calculations, and demonstrate that its magnetic ground state matches the experimental spin structure.This project was funded in part by the German Research Foundation (DFG) under the individual research Grant IN 209/9-1, via the project C03 of the Collaborative Research Center SFB 1143 (project-id 247310070) at the TU Dresden, and the Würzburg-Dresden Cluster of Excellence on Complexity and Topology in Quantum Matter—ct.qmat (EXC 2147, project-id 390858490). SA thanks A Popov (IFW, Dresden) and M Vojta (TU Dresden) for fruitful discussions and acknowledges financial support from the German Research Foundation (DFG) under Grant No. AV 169/3-1. We also acknowledge V Joyet and S Djellit for technical assistance and Institut Laue-Langevin, Grenoble (France) for providing neutron beam time.Peer reviewe
Stripe-yzmagnetic order in the triangular-lattice antiferromagnet KCeS2
Yb- and Ce-based delafossites were recently identified as effective spin-1/2 antiferromagnets on the triangular lattice. Several Yb-based systems, such as NaYbO2, NaYbS2, and NaYbSe2, exhibit no long-range order down to the lowest measured temperatures and therefore serve as putative candidates for the realization of a quantum spin liquid. However, their isostructural Ce-based counterpart KCeS2 exhibits magnetic order below TN = 400 mK, which was so far identified only in thermodynamic measurements. Here we reveal the magnetic structure of this long-range ordered phase using magnetic neutron diffraction. We show that it represents the so-called 'stripe-yz' type of antiferromagnetic order with spins lying approximately in the triangular-lattice planes orthogonal to the nearest-neighbor Ce–Ce bonds. No structural lattice distortions are revealed below TN, indicating that the triangular lattice of Ce3+ ions remains geometrically perfect down to the lowest temperatures. We propose an effective Hamiltonian for KCeS2, based on a fit to the results of ab initio calculations, and demonstrate that its magnetic ground state matches the experimental spin structure
Interplay of structural distortions, dielectric effects and magnetic order in multiferroic GdMnO3
Multiferroic materials are characterized by simultaneous magnetic and ferroelectric ordering making them good candidates for magneto-electrical applications. We conducted thermal expansion and magnetostriction measurements in magnetic fields up to 14 T on perovskitic GdMnO3 by highresolution capacitive dilatometry in an effort to determine all longitudinal and transversal components of the magnetostriction tensor. Below the ordering temperature T (N) = 42 K, i.e., within the different complex (incommensurate or complex) antiferromagnetic phases, lattice distortions of up to 100 ppm have been found. Although no change of the lattice symmetry occurs, the measurements reveal strong magneto-structural phenomena, especially in the incommensurate sinusoidal antiferromagnetic phase. A strong anisotropy of the magnetoelastic properties was found, in good agreement with the type and propagation vector of the magnetic structure. We demonstrate that our capacitive dilatometry can detect lattice expansion effects and changes of the dielectric permittivity simultaneously because the sample is housed inside the capacitor. A separation of both effects is possible by shielding the sample. Dielectric transitions could be detected by this method and compared to the critical values of H and T in the magnetic phase diagram. Dielectric changes measured at 1 kHz excitation frequency are detected in GdMnO3 at about 180 K, and between 10 K and 25 K in the canted antiferromagnetic structure which is characterized by a complex magnetic order on both the Gd- and Mn-sites