| 1. |
- Bonnet, Cecilia, et al.
(författare)
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Eye Movements in Ephedrone-Induced Parkinsonism
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:8, s. e104784-
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Tidskriftsartikel (refereegranskat)abstract
- Patients with ephedrone parkinsonism (EP) show a complex, rapidly progressive, irreversible, and levodopa non-responsive parkinsonian and dystonic syndrome due to manganese intoxication. Eye movements may help to differentiate parkinsonian syndromes providing insights into which brain networks are affected in the underlying disease, but they have never been systematically studied in EP. Horizontal and vertical eye movements were recorded in 28 EP and compared to 21 Parkinson's disease (PD) patients, and 27 age- and gender-matched healthy subjects using standardized oculomotor tasks with infrared videooculography. EP patients showed slow and hypometric horizontal saccades, an increased occurrence of square wave jerks, long latencies of vertical antisaccades, a high error rate in the horizontal antisaccade task, and made more errors than controls when pro-and antisaccades were mixed. Based on oculomotor performance, a direct differentiation between EP and PD was possible only by the velocity of horizontal saccades. All remaining metrics were similar between both patient groups. EP patients present extensive oculomotor disturbances probably due to manganese-induced damage to the basal ganglia, reflecting their role in oculomotor system.
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| 2. |
- Bhowmick, Somnath, et al.
(författare)
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X-ray absorption spectra : Graphene, h-BN, and their alloy
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:15, s. 155108-
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Tidskriftsartikel (refereegranskat)abstract
- Using first-principles density functional theory calculations, in conjunction with the Mahan-Nozieres-de Dominicis theory, we calculate the x-ray absorption spectra of the alloys of graphene and monolayer hexagonal boron nitride on a Ni (111) substrate. The chemical neighborhood of the constituent atoms (B, C, and N) inside the alloy differs from that of the parent phases. In a systematic way, we capture the change in the K-edge spectral shape, depending on the chemical neighborhood of B, C, and N. Our work also reiterates the importance of the dynamical core-hole screening for a proper description of the x-ray absorption process in sp(2)-bonded layered materials.
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| 3. |
- Bidermane, Ieva, et al.
(författare)
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Experimental and theoretical study of electronic structure of lutetium bi-phthalocyanine
- 2013
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 138:23, s. 234701-
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Tidskriftsartikel (refereegranskat)abstract
- Using Near Edge X-Ray Absorption Fine Structure (NEXAFS) Spectroscopy, the thickness dependent formation of Lutetium Phthalocyanine (LuPc2) films on a stepped passivated Si(100)2x1 reconstructed surface was studied. Density functional theory (DFT) calculations were employed to gain detailed insights into the electronic structure. Photoelectron spectroscopy measurements have not revealed any noticeable interaction of LuPc2 with the H-passivated Si surface. The presented study can be considered to give a comprehensive description of the LuPc2 molecular electronic structure. The DFT calculations reveal the interaction of the two molecular rings with each other and with the metallic center forming new kinds of orbitals in between the phthalocyanine rings, which allows to better understand the experimentally obtained NEXAFS results.
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| 4. |
- Calmels, Lionel, et al.
(författare)
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Atomic site sensitivity of the energy loss magnetic chiral dichroic spectra of complex oxides
- 2011
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 109:7, s. 07D328-
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Tidskriftsartikel (refereegranskat)abstract
- The quantitative analysis of magnetic oxide core level spectra can become complicated when the magnetic atoms are located at several nonequivalent atomic sites in the crystal. This is, for instance, the case for Fe atoms in magnetite, which are located in tetrahedral and octahedral atomic sites; in this case, the x-ray magnetic circular dichroic (XMCD) spectra recorded at the L-2,L-3 edge of Fe contain contributions from the different nonequivalent atomic sites, which unfortunately cannot be separated. Energy loss magnetic chiral dichroic (EMCD) spectra are the transmission electron microscope analogies of the XMCD spectra. One of the important differences between these two techniques of magnetic analysis is that EMCD uses a fast electron beam instead of polarized light. The fast electrons behave like Bloch states in the sample, and the fine structure of the EMCD spectra is strongly influenced by channeling and dynamical diffraction effects. These effects can be adjusted by changing the experimental configuration. We use theoretical calculations, which include dynamical diffraction effects and in which electronic transitions are treated in the atomic multiplet formalism, to show that the relative weight of the Fe atoms in different nonequivalent atomic sites can be changed by a proper choice of the position of the detector and of the magnetite sample orientation and thickness. We conclude that EMCD spectra could be used to isolate the magnetic contribution of atoms in each of the nonequivalent atomic sites, which would not be possible with XMCD techniques. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3556769]
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| 5. |
- Calmels, Lionel, et al.
(författare)
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Momentum-resolved EELS and EMCD spectra from the atomic multiplet theory : application to magnetite
- 2010
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 110:8, s. 1042-1045
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Tidskriftsartikel (refereegranskat)abstract
- While the energy loss near edge structures of metallic crystals can be calculated with a good accuracy using density functional theory based codes, core-level spectra of transition metal oxides show pronounced multiplet effects which are better described by atomic multiplet codes. We describe the formalism which allows to calculate momentum-resolved electron energy loss spectra in the electric dipole approximation from the atomic multiplet theory, and we apply this formalism to the calculation of energy loss magnetic chiral dichroic spectra of magnetic transition metal oxides. Explicit results are given for magnetite Fe3O4.
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| 6. |
- Delczeg-Czirjak, Erna K., et al.
(författare)
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Stabilization of the tetragonal distortion of Fe chi Co1-chi alloys by C impurities : A potential new permanent magnet
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:14, s. 144403-
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Tidskriftsartikel (refereegranskat)abstract
- We have analyzed by density functional theory calculations the structural and magnetic properties of Fe-Co alloys doped by carbon. In analogy with the formation of martensite in steels we predict that such a structure also forms for Fe-Co alloys in a wide range of concentrations. These alloys are predicted to have a stable tetragonal distortion, which in turn leads to an enhanced magnetocrystalline anisotropy energy of up to 0.75 MJ/m(3) and a saturated magnetization field of 1.9 T.
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| 7. |
- Edström, Alexander, et al.
(författare)
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Electronic structure and magnetic properties of L1(0) binary alloys
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:1, s. 014402-
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Tidskriftsartikel (refereegranskat)abstract
- We present a systematic study of the magnetic properties of L1(0) binary alloys FeNi, CoNi, MnAl, and MnGa via two different density functional theory approaches. Our calculations show large magnetocrystalline anisotropies in the order 1 MJ/m(3) or higher for CoNi, MnAl, and MnGa, while FeNi shows a somewhat lower value in the range 0.48-0.77 MJ/m(3). Saturation magnetization values of 1.3 MA/m, 1.0 MA/m, 0.8 MA/m, and 0.9 MA/m are obtained for FeNi, CoNi, MnAl, and MnGa, respectively. Curie temperatures are evaluated via Monte Carlo simulations and show T-C = 916 K and T-C = 1130 K for FeNi and CoNi, respectively. For Mn-based compounds Mn-rich off-stoichiometric compositions are found to be important for the stability of a ferro- or ferrimagnetic ground state with T-C greater than 600 K. The effect of substitutional disorder is studied and found to decrease both magnetocrystalline anisotropies and Curie temperatures in FeNi and CoNi.
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| 8. |
- Edström, Alexander, 1988-
(författare)
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Theoretical Magnet Design : From the electronic structure of solid matter to new permanent magnets
- 2014
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A good permanent magnet should possess a large saturation magnetisation (Ms), large mag- netocrystalline anisotropy energy (MAE) and a high Curie temperature (TC). A difficult but important challenge to overcome for a sustainable permanent magnet industry is to find novel magnetic materials, exhibiting a large MAE, without the use of scarcely available elements such as rare-earth metals. The purpose of this thesis is to apply computational methods, including density functional theory and Monte Carlo simulations, to assess the three above mentioned permanent magnet properties and in particular to discover new replacement materials with large MAE without the use of critical materials such as rare-earths.One of the key results is the theoretical prediction of a tetragonal phase of Fe1−xCox-C with large Ms and significantly increased MAE which is later also experimentally confirmed. Furthermore, other potential materials are surveyed and in particular the properties of a number of binary alloys in the L10 structure, FeNi, CoNi, MnAl and MnGa, are thoroughly investigated and shown to posses the desired properties under certain conditions.
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| 9. |
- Elgazzar, Saad, et al.
(författare)
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Ab initio computational and experimental investigation of the electronic structure of actinide 218 materials
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:23, s. 235117-
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Tidskriftsartikel (refereegranskat)abstract
- We report a comprehensive investigation of the electronic structure and magnetic properties of actinide 218 compounds, which crystallize in the tetragonal Ho2CoGa8 crystal structure. Specifically, we study experimentally the group of plutonium-based compounds Pu2MGa8 (with M=Rh, Co, and Fe), which are structurally related to the unconventional superconductors PuCoGa5 and PuRhGa5 and are measured to be nonmagnetic and nonsuperconducting down to 2 K, yet displaying relatively high linear specific-heat coefficients of 61 to 133 mJ/mol K-2. We perform density-functional theory based calculations, in which we apply three different approaches to access the tendency of 5f electron localization, the local spin-density approximation (LSDA) LSDA+U, and the 5f open-core approach. For comparison to the above-mentioned compounds we also investigate computationally the plutonium compounds with M=Ir and Pd, the uranium-based compounds U2MGa8 (with M=Co, Fe, Rh, and Ru), as well as Np2CoGa8, and Am2CoGa8. On the basis of ab initio LSDA calculations we optimize the equilibrium lattice parameters and the internal fractional coordinates within the Ho2CoGa8 crystal structure. The obtained lattice parameters are in relatively good agreement with experimental values, when we assume delocalized 5f states for all compounds except Am2CoGa8. We discuss the computed electronic structures and the theoretical Fermi surfaces. For the Pu-218 compounds we find that LSDA calculations, in which the 5f's are treated as delocalized, predict a magnetically ordered ground state, whereas LSDA+U calculations predict a nonmagnetic ground state in accordance with experiment. For the U-218 compounds the LSDA itinerant 5f approach predicts a nonmagnetic ground state, in accordance with available experimental data. For Am2CoGa8 our calculations are consistent with the scenario of localized 5f electrons. We find that, on account of the elongated tetragonal structure, most of the theoretical Fermi surfaces are quasi-two-dimensional.
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| 10. |
- Elgazzar, S., et al.
(författare)
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Electronic structure and Fermi surface of paramagnetic and antiferromagnetic UPt2Si2
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 86:7, s. 075104-
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Tidskriftsartikel (refereegranskat)abstract
- We report density functional theory-based calculations of the electronic structure and Fermi surface properties of the intermetallic uranium compound UPt2Si2, which orders antiferromagnetically at TN=32 K with a total magnetic moment of 2μB/U-atom and exhibits a moderate mass enhancement in the specific-heat coefficient. Our investigation is carried out using relativistic, full-potential band-structure methods within the framework of the local spin density approximation (LSDA), the LSDA with orbital polarization correction (LSDA+OPC), and the LSDA supplemented with an additional Hubbard U (LSDA+U). We find that the LSDA+OPC scheme predicts the total magnetic moment in best agreement with experiment; from this we infer that the 5f electrons in UPt2Si2 are orbitally polarized, mostly itinerant, and exhibit only a slight tendency toward localization. Our total energy calculations predict UPt2Si2 to form in the CaBe2Si2 (P4/nmm) structure, in contrast to URu2Si2 (ThCr2Si2: I4/mmm). The theoretical Fermi surfaces are also studied for the nonmagnetic and antiferromagnetic phases with the employed computational schemes and are found to be quasi-two-dimensional. At the antiferromagnetic transition, the Fermi surface is found to become more two-dimensional with small regions of gapping.
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| 11. |
- Kocevski, Vancho, et al.
(författare)
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Transition between direct and indirect band gap in silicon nanocrystals
- 2013
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 87:24, s. 245401-
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Tidskriftsartikel (refereegranskat)abstract
- Using ground-state density functional theory we study the transition from indirect to direct band gap in hydrogen-terminated silicon nanocrystals (NCs) as a function of decreasing diameter. The studied range, from 1.0 to 4.6 nm diameter of nanocrystals, with spherical and Wulff-shape NCs, covers the transition from nano-to bulk regime. A change in the symmetry of the lowest unoccupied state as a function of decreasing NC diameter is observed, gradually increasing the oscillator strength of transitions from the highest occupied to the lowest unoccupied state. Real space and Fourier space characteristics of highest occupied and lowest unoccupied states are explored in detail and linked to a smooth transition from nano-to bulk regime.
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| 12. |
- Krivanek, Ondrej L., et al.
(författare)
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Toward Single Mode, Atomic Size Electron Vortex Beams
- 2014
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Ingår i: Microscopy and Microanalysis. - 1431-9276 .- 1435-8115. ; 20:3, s. 832-836
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Tidskriftsartikel (refereegranskat)abstract
- We propose a practical method of producing a single mode electron vortex beam suitable for use in a scanning transmission electron microscope (STEM). The method involves using a holographic "fork" aperture to produce a row of beams of different orbital angular momenta, as is now well established, magnifying the row so that neighboring beams are separated by about 1 mu m, selecting the desired beam with a narrow slit, and demagnifying the selected beam down to 1-2 angstrom in size. We show that the method can be implemented by adding two condenser lenses plus a selection slit to a straight-column cold-field emission STEM. It can also be carried out in an existing instrument, the monochromated Nion high-energy-resolution monochromated electron energy-loss spectroscopy-STEM, by using its monochromator in a novel way. We estimate that atom-sized vortex beams with <= 20 pA of current should be attainable at 100-200 keV in either instrument.
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| 13. |
- Kudrnovsky, J., et al.
(författare)
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Unified approach to electronic, thermodynamical, and transport properties of Fe3Si and Fe3Al alloys
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 90:13, s. 134408-
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Tidskriftsartikel (refereegranskat)abstract
- The electronic, thermodynamical, and transport properties of ordered Fe3X (X = Al, Si) alloys are studied from first principles. We present here a unified approach to the phase stability, the estimate of the Curie temperature, the temperature dependence of sublattice magnetizations, magnon spectra, the spin-stiffnesses, and residual resistivities. An important feature of the present study is that all calculated physical properties are determined in the framework of the same first-principles electronic structure model combined with the effective Ising and Heisenberg Hamiltonians used for study of the thermodynamical properties of alloys. Curie temperatures, spin-stiffnesses, and magnon spectra are determined using the same calculated exchange integrals. Finally, the transport properties are calculated using the linear-response theory. Our theoretical estimates compare well with available experimental data. In particular, calculations predict (in agreement with experiment) the ordered D0(3) phase as the ground-state alloy structure, demonstrate that a correct relation of Curie temperatures of Fe3Al/Fe3Si alloys can be obtained only by going beyond a simple mean-field approximation, provide reasonable estimates of spin-stiffnesses, and give resistivities compatible with structural disorder observed in the experiment. Although the calculated temperature dependences of the Fe magnetization on different sublattices are similar, they nevertheless deviate more than in the experiment, and we discuss a possible origin.
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| 14. |
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| 15. |
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| 16. |
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| 17. |
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| 18. |
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| 19. |
- Lidbaum, Hans, et al.
(författare)
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Reciprocal and real space maps for EMCD experiments
- 2010
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 110:11, s. 1380-1389
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Tidskriftsartikel (refereegranskat)abstract
- Electron magnetic chiral dichroism (EMCD) is an emerging tool for quantitative measurements of magnetic properties using the transmission electron microscope (TEM), with the possibility of nanometer resolution. The geometrical conditions, data treatment and electron gun settings are found to influence the EMCD signal. In this article, particular care is taken to obtain a reliable quantitative measurement of the ratio of orbital to spin magnetic moment using energy filtered diffraction patterns. For this purpose, we describe a method for data treatment, normalization and selection of mirror axis. The experimental results are supported by theoretical simulations based on dynamical diffraction and density functional theory. Special settings of the electron gun, so called telefocus mode, enable a higher intensity of the electron beam, as well as a reduction of the influence from artifacts on the signal. Using these settings, we demonstrate the principle of acquiring real space maps of the EMCD signal. This enables advanced characterization of magnetic materials with superior spatial resolution.
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| 20. |
- Mukherjee, Soham, et al.
(författare)
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Microscopic description of the evolution of the local structure and an evaluation of the chemical pressure concept in a solid solution
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 89:22, s. 224105-
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Tidskriftsartikel (refereegranskat)abstract
- Extended x-ray absorption fine-structure studies have been performed at the Zn K and Cd K edges for a series of solid solutions of wurtzite Zn1-xCdxS samples with x = 0.0, 0.1, 0.25, 0.5, 0.75, and 1.0, where the lattice parameter as a function of x evolves according to the well-known Vegard's law. In conjunction with extensive, large-scale first-principles electronic structure calculations with full geometry optimizations, these results establish that the percentage variation in the nearest-neighbor bond distances are lower by nearly an order of magnitude compared to what would be expected on the basis of lattice parameter variation, seriously undermining the chemical pressure concept. With experimental results that allow us to probe up to the third coordination shell distances, we provide a direct description of how the local structure, apparently inconsistent with the global structure, evolves very rapidly with interatomic distances to become consistent with it. We show that the basic features of this structural evolution with the composition can be visualized with nearly invariant Zn-S-4 and Cd-S-4 tetrahedral units retaining their structural integrity, while the tilts between these tetrahedral building blocks change with composition to conform to the changing lattice parameters according to the Vegard's law within a relatively short length scale. These results underline the limits of applicability of the chemical pressure concept that has been a favored tool of experimentalists to control physical properties of a large variety of condensed matter systems.
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| 21. |
- Muto, S., et al.
(författare)
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Parameter-free extraction of EMCD from an energy-filtered diffraction datacube using multivariate curve resolution
- 2013
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Ingår i: Ultramicroscopy. - : Elsevier BV. - 0304-3991 .- 1879-2723. ; 125, s. 89-96
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Tidskriftsartikel (refereegranskat)abstract
- We present a parameter-free method of extraction of the electron magnetic circular dichroism spectra from energy-filtered diffraction patterns measured on a crystalline specimen. The method is based on a multivariate curve resolution technique. The main advantage of the proposed method is that it allows extraction of the magnetic signal regardless of the symmetry and orientation of the crystal, as long as there is a sufficiently strong magnetic component of the signal in the diffraction plane. This method essentially overcomes difficulties in extraction of the EMCD signal caused by complexity of dynamical diffraction effects.
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| 22. |
- Muto, Shunsuke, et al.
(författare)
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Quantitative characterization of nanoscale polycrystalline magnets with electron magnetic circular dichroism
- 2014
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 3138-
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Tidskriftsartikel (refereegranskat)abstract
- Electron magnetic circular dichroism (EMCD) allows the quantitative, element-selective determination of spin and orbital magnetic moments, similar to its well-established X-ray counterpart, X-ray magnetic circular dichroism (XMCD). As an advantage over XMCD, EMCD measurements are made using transmission electron microscopes, which are routinely operated at sub-nanometre resolution, thereby potentially allowing nanometre magnetic characterization. However, because of the low intensity of the EMCD signal, it has not yet been possible to obtain quantitative information from EMCD signals at the nanoscale. Here we demonstrate a new approach to EMCD measurements that considerably enhances the outreach of the technique. The statistical analysis introduced here yields robust quantitative EMCD signals. Moreover, we demonstrate that quantitative magnetic information can be routinely obtained using electron beams of only a few nanometres in diameter without imposing any restriction regarding the crystalline order of the specimen.
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| 23. |
- Nolting, Frithjof, et al.
(författare)
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Anisotropy of the L-2,L-3 x-ray magnetic linear dichroism of Fe films on GaAs : Experiment and ab initio theory
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:18, s. 184415-
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Tidskriftsartikel (refereegranskat)abstract
- We report investigations of the anisotropy of the x-ray magnetic linear dichroism (XMLD) of thin single-crystalline Fe films on GaAs substrates with film thicknesses of 3 nm and 7 nm, respectively. The orientation of the in-plane Fe magnetization with respect to the crystal axes is stepwise rotated from the [1 1 0] to the [0 1 0] direction and the Fe L-2,L-3 XMLD spectrum is measured at every orientation step. A highly anisotropic XMLD signal at the Fe L-2 and L-3 edges is observed, which origin is analyzed in detail. We show that the measured anisotropic XMLD spectra are in reasonable agreement with ab initio calculated spectra. The XMLD anisotropy is shown to be a consequence of the cubic crystal-field split density of 3d states, which are selectively probed by transitions from the spin-orbit and exchange-split 2p core levels. We furthermore investigate computationally the influences of the spin-orbit interaction of the Fe 3d valence electrons as well as of stress in the Fe films. The Fe 3d spin-orbit interaction only leads to small modifications of the XMLD spectra, whereas tetragonal deformation of the films can cause a larger modification of the spectra.
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| 24. |
- Oppeneer, Peter M., et al.
(författare)
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Electronic structure theory of the hidden-order material URu2Si2
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 82:20, s. 205103-
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Tidskriftsartikel (refereegranskat)abstract
- We report a comprehensive electronic structure investigation of the paramagnetic (PM), the large moment antiferromagnetic (LMAF), and the hidden order (HO) phases of URu2Si2. We have performed relativistic full-potential calculations on the basis of the density-functional theory, employing different exchange-correlation functionals to treat electron correlations within the open 5f shell of uranium. Specifically, we investigate-through a comparison between calculated and low-temperature experimental properties-whether the 5f electrons are localized or delocalized in URu2Si2. The local spin-density approximation (LSDA) and generalized gradient approximation (GGA) are adopted to explore itinerant 5f behavior, the GGA plus additional strong Coulomb interaction (GGA+U approach) is used to approximate moderately localized 5f states, and the 5f-core approximation is applied to probe potential properties of completely localized uranium 5f states. We also performed local-density approximation plus dynamical mean-field theory calculations (DMFT) to investigate the temperature evolution of the quasiparticle states at 100 K and above, unveiling a progressive opening of a quasiparticle gap at the chemical potential when temperature is reduced. A detailed comparison of calculated properties with known experimental data demonstrates that the LSDA and GGA approaches, in which the uranium 5f electrons are treated as itinerant, provide an excellent explanation of the available low-temperature experimental data of the PM and LMAF phases. We show furthermore that due to a material-specific Fermi-surface instability a large, but partial, Fermi-surface gapping of up to 750 K occurs upon antiferromagnetic symmetry breaking. The occurrence of the HO phase is explained through dynamical symmetry breaking induced by a mode of long-lived antiferromagnetic spin fluctuations. This dynamical symmetry breaking model explains why the Fermi-surface gapping in the HO phase is similar but smaller than that in the LMAF phase and it also explains why the HO and LMAF phases have the same Fermi surfaces yet different order parameters. A suitable order parameter for the HO is proposed to be the Fermi-surface gap, and the dynamic spin-spin correlation function is further suggested as a secondary order parameter.
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| 25. |
- Oppeneer, Peter M., et al.
(författare)
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Spin and orbital hybridization at specifically nested Fermi surfaces in URu(2)Si(2)
- 2011
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 84:24, s. 241102-
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Tidskriftsartikel (refereegranskat)abstract
- The Fermi-surface (FS) nesting properties of URu(2)Si(2) are analyzed with particular focus on their implication for the mysterious hidden order phase. We show that there exist two Fermi surfaces that exhibit a strong nesting at the antiferromagnetic wave vector Q(0) = (0,0,1). The corresponding energy dispersions fulfill the relation epsilon(1)(k) = -epsilon(2)(k +/- Q(0)) at eight FS hot-spot lines. The spin-orbital characters of the involved 5f states are distinct (j(z) = +/-5/2 vs +/-3/2) and hence the degenerate Dirac crossings are symmetry protected in the nonmagnetic normal state. Dynamical symmetry breaking through an Ising-like spin and orbital excitation mode with Delta j(z) = +/-1 induces a hybridization of the two states, causing substantial FS gapping. Concomitant spin and orbital currents in the uranium planes give rise to a rotational symmetry breaking.
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