| 1. |
- Kádas, Krisztina, et al.
(författare)
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AlM2B2 (M = Cr, Mn, Fe, Co, Ni) : a group of nanolaminated materials
- 2017
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Ingår i: Journal of Physics. - : Institute of Physics Publishing (IOPP). - 0953-8984 .- 1361-648X. ; 29:15
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Tidskriftsartikel (refereegranskat)abstract
- Combining theory with experiments, we study the phase stability, elastic properties, electronic structure and hardness of layered ternary borides AlCr2B2, AlMn2B2, AlFe2B2, AlCo2B2, and AlNi2B2. We find that the first three borides of this series are stable phases, while AlCo2B2 and AlNi2B2 are metastable. We show that the elasticity increases in the boride series, and predict that AlCr2B2, AlMn2B2, and AlFe2B2 are more brittle, while AlCo2B2 and AlNi2B2 are more ductile. We propose that the elasticity of AlFe2B2 can be improved by alloying it with cobalt or nickel, or a combination of them. We present evidence that these ternary borides represent nanolaminated systems. Based on SEM measurements, we demonstrate that they exhibit the delamination phenomena, which leads to a reduced hardness compared to transition metal mono-and diborides. We discuss the background of delamination by analyzing chemical bonding and theoretical work of separation in these borides.
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| 2. |
- Abdel-Hafiez, Mahmoud, et al.
(författare)
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From Insulator to Superconductor : A Series of Pressure-Driven Transitions in Quasi-One-Dimensional TiS3 Nanoribbons
- 2024
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6984 .- 1530-6992. ; 24:18, s. 5562-5569
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal trichalcogenides (TMTCs) offer remarkable opportunities for tuning electronic states through modifications in chemical composition, temperature, and pressure. Despite considerable interest in TMTCs, there remain significant knowledge gaps concerning the evolution of their electronic properties under compression. In this study, we employ experimental and theoretical approaches to comprehensively explore the high-pressure behavior of the electronic properties of TiS3, a quasi-one-dimensional (Q1D) semiconductor, across various temperature ranges. Through high-pressure electrical resistance and magnetic measurements at elevated pressures, we uncover a distinctive sequence of phase transitions within TiS3, encompassing a transformation from an insulating state at ambient pressure to the emergence of an incipient superconducting state above 70 GPa. Our findings provide compelling evidence that superconductivity at low temperatures of ∼2.9 K is a fundamental characteristic of TiS3, shedding new light on the intriguing high-pressure electronic properties of TiS3 and underscoring the broader implications of our discoveries for TMTCs in general.
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| 3. |
- Arapan, S., et al.
(författare)
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Influence of antiphase boundary of the MnAl tau-phase on the energy product
- 2019
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Ingår i: Physical Review Materials. - : American Physical Society. - 2475-9953. ; 3:6
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we use a multiscale approach to describe a realistic model of a permanent magnet based on MnAl tau-phase and elucidate how the antiphase boundary defects present in this material affect the energy product. We show how the extrinsic properties of a microstructure depend on the intrinsic properties of a structure with defects by performing micromagnetic simulations. For an accurate estimation of the energy product of a realistic permanent magnet based on the MnAl tau-phase with antiphase boundaries, we quantify exchange interaction strength across the antiphase boundary defect with a simple approach derived from first-principles calculations. These two types of calculations, performed at different scales, are linked via atomistic spin-dynamics simulations.
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| 4. |
- Arora, Monika, et al.
(författare)
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Magnetic Damping in Polycrystalline Thin-Film Fe-V Alloys
- 2021
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Ingår i: Physical Review Applied. - : American Physical Society. - 2331-7019. ; 15:5
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Tidskriftsartikel (refereegranskat)abstract
- We report on the magnetic damping properties of polycrystalline Fe-V alloy thin films that are deposited at room temperature. By varying the concentration of V in the alloy, the saturation magnetization can be adjusted from that of Fe to near zero. We show that exceptionally low values of the damping parameter can be maintained over the majority of this range, with a minimum damping at approximately 15%-20% V concentration. Such a minimum is qualitatively reproduced with ab initio calculations of the damping parameter, although at a concentration closer to 10% V. The measured intrinsic damping has a minimum value of (1.53 +/- 0.08) x 10-3, which is approximately a factor of 3 higher than our calculated value of 0.48 x 10-3. From first-principles theory, we outline the factors that are mainly responsible for the trend of the damping parameter in these alloys. In particular, the band structure and resulting damping mechanism is shown to change at V concentrations greater than approximately 35% V content.
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| 5. |
- Azimi Mousolou, Vahid, et al.
(författare)
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Entanglement duality in spin-spin interactions
- 2022
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Ingår i: Physical Review A: covering atomic, molecular, and optical physics and quantum information. - : American Physical Society (APS). - 2469-9926 .- 2469-9934. ; 106:3
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Tidskriftsartikel (refereegranskat)abstract
- We examine entanglement of thermal states for spin-1/2 dimers in external magnetic fields. Entanglement transition in the temperature-magnetic-field plane demonstrates a duality in spin-spin interactions. This identifies a pair of dual categories of symmetric and antisymmetric dimers with each category classified into toric entanglement classes. The entanglement transition line is preserved from each toric entanglement class to its dual toric class. The toric classification is an indication of the topological signature of the entanglement, which bring about topological stability that could be relevant for quantum information processing.
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| 6. |
- Azimi Mousolou, Vahid, et al.
(författare)
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Hierarchy of magnon mode entanglement in antiferromagnets
- 2020
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Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 102:22
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Tidskriftsartikel (refereegranskat)abstract
- Continuous variable entanglement between magnon modes in Heisenberg antiferromagnets with Dzyaloshinskii-Moriya (DM) interaction is examined. Different bosonic modes are identified, which allows us to establish a hierarchy of magnon entanglement. We argue that entanglement between magnon modes is determined by a simple lattice-specific parameter, together with the ratio of the strengths of the DM and Heisenberg exchange interactions, and that magnon entanglement can be detected by means of quantum homodyne techniques. As an illustration of the relevance of our findings for possible entanglement experiments in the solid state, a typical antiferromagnet with the perovskite crystal structure is considered, and it is shown that long wave length magnon modes have a maximal degree of entanglement.
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| 7. |
- Azimi Mousolou, Vahid, et al.
(författare)
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Magnon-magnon entanglement and its quantification via a microwave cavity
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:22
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Tidskriftsartikel (refereegranskat)abstract
- Quantum magnonics is an emerging research field, with great potential for applications in magnon based hybrid systems and quantum information processing. Quantum correlation, such as entanglement, is a central resource in many quantum information protocols that naturally comes about in any study toward quantum technologies. This applies also to quantum magnonics. Here, we investigate antiferromagnetic coupling of two ferromagnetic sublattices that can have two different magnon modes. We show how this may lead to experimentally measurable bipartite continuous-variable magnon-magnon entanglement. The entanglement can be fully characterized via a single squeezing parameter or, equivalently, entanglement parameter. The clear relation between the entanglement parameter and the Einstein, Podolsky, and Rosen (EPR) function of the ground state opens up for experimental quantification magnon-magnon continuous-variable entanglement and EPR nonlocality. We propose a practical experimental realization to measure the EPR function of the ground state, in a setting that relies on magnon-photon interaction in a microwave cavity.
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| 8. |
- Azimi Mousolou, Vahid, et al.
(författare)
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Transmon probe for quantum characteristics of magnons in antiferromagnets
- 2023
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 108:9
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Tidskriftsartikel (refereegranskat)abstract
- The detection of magnons and their quantum properties, especially in antiferromagnetic (AFM) materials, is a substantial step to realize many ambitious advances in the study of nanomagnetism and the development of energy efficient quantum technologies. The recent development of hybrid systems based on superconducting circuits provides the possibility to engineer quantum sensors that exploit different degrees of freedom. Here, we examine the magnon-photon-transmon hybridization based on bipartite AFM materials, which gives rise to an effective coupling between a transmon qubit and magnons in a bipartite AFM. We demonstrate how magnon modes, their chiralities, and quantum properties, such as nonlocality and two-mode magnon entanglement in bipartite AFMs, can be characterized through the Rabi frequency of the superconducting transmon qubit.
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| 9. |
- Baglai, Mikhail, et al.
(författare)
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Giant anisotropy of Gilbert damping in a Rashba honeycomb antiferromagnet
- 2020
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 101:10
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Tidskriftsartikel (refereegranskat)abstract
- Giant Gilbert damping anisotropy is identified as a signature of strong Rashba spin-orbit coupling in a two-dimensional antiferromagnet on a honeycomb lattice. The phenomenon originates in spin-orbit-induced splitting of conduction electron subbands that strongly suppresses certain spin-flip processes. As a result, the spin-orbit interaction is shown to support an undamped nonequilibrium dynamical mode that corresponds to an ultrafast in-plane Neel vector precession and a constant perpendicular-to-the-plane magnetization. The phenomenon is illustrated on the basis of a two-dimensional s-d-like model. Spin-orbit torques and conductivity are also computed microscopically for this model. Unlike Gilbert damping, these quantities are shown to reveal only a weak anisotropy that is limited to the semiconductor regime corresponding to the Fermi energy staying in the close vicinity of the antiferromagnetic gap.
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| 10. |
- Belotcerkovtceva, Daria, et al.
(författare)
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Insights and Implications of Intricate Surface Charge Transfer and sp3-Defects in Graphene/Metal Oxide Interfaces
- 2022
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 14:31, s. 36209-36216
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Tidskriftsartikel (refereegranskat)abstract
- Adherence of metal oxides to graphene is of fundamental significance to graphene nanoelectronic and spintronic interfaces. Titanium oxide and aluminum oxide are two widely used tunnel barriers in such devices, which offer optimum interface resistance and distinct interface conditions that govern transport parameters and device performance. Here, we reveal a fundamental difference in how these metal oxides interface with graphene through electrical transport measurements and Raman and photoelectron spectroscopies, combined with ab initio electronic structure calculations of such interfaces. While both oxide layers cause surface charge transfer induced p-type doping in graphene, in sharp contrast to TiOx, the AlOx/graphene interface shows the presence of appreciable sp3 defects. Electronic structure calculations disclose that significant p-type doping occurs due to a combination of sp3 bonds formed between C and O atoms at the interface and possible slightly off-stoichiometric defects of the aluminum oxide layer. Furthermore, the sp3 hybridization at the AlOx/graphene interface leads to distinct magnetic moments of unsaturated bonds, which not only explicates the widely observed low spin-lifetimes in AlOx barrier graphene spintronic devices but also suggests possibilities for new hybrid resistive switching and spin valves.
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| 11. |
- Benter, Sandra, et al.
(författare)
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Tuneable 2D surface Bismuth incorporation on InAs nanosheets
- 2023
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Ingår i: Nanoscale. - : Royal Society of Chemistry. - 2040-3364 .- 2040-3372. ; 15:21, s. 9551-9559
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Tidskriftsartikel (refereegranskat)abstract
- The chemical bonding at the interface between compound semiconductors and metals is central in determining electronic and optical properties. In this study, new opportunities for controlling this are presented for nanostructures. We investigate Bi adsorption on 2D wurtzite InAs (1120) nanosheets and find that temperature-controlled Bi incorporation in either anionic- or cationic-like bonding is possible in the easily accesible range between room temperature and 400 degrees C. This separation could not be achieved for ordinary zinc blende InAs(110) surfaces. As the crystal structures of the two surfaces have identical nearest neighbour configurations, this indicates that overall geometric differences can significantly alter the adsorption and incorporation. Ab initio theoretical modelling confirms observed adsorption results, but indicate that both the formation energies as well as kinetic barriers contributes to the observed temperature dependent behaviour. Further, we find that the Bi adsorption rate can differ by at least 2.5 times between the two InAs surfaces while being negligible for standard Si substrates under similar deposition conditions. This, in combination with the observed interface control, provides an excellent opportunity for tuneable Bi integration on 2D InAs nanostructures on standard Si substrates.
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| 12. |
- Bergman, Anders, 1978-, et al.
(författare)
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Magnon softening in a ferromagnetic monolayer : A first-principles spin dynamics study
- 2010
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 81:14, s. 144416-
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Tidskriftsartikel (refereegranskat)abstract
- We study the Fe/W(110) monolayer system through a combination of first-principles calculations and atomistic spin dynamics simulations. We focus on the dispersion of the spin-waves parallel to the [001] direction. Our results compare favorably with the experimental data of Prokop et al. [Phys. Rev. Lett. 102, 177206 (2009)] and correctly capture a drastic softening of the magnon spectrum, with respect to bulk bcc Fe. The suggested shortcoming of the itinerant electron model, in particular that given by density functional theory, is refuted. We also demonstrate that finite-temperature effects are significant, and that atomistic spin dynamics simulations represent a powerful tool with which to include these.
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| 13. |
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| 14. |
- Björnson, Kristofer, et al.
(författare)
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In Situ Pseudopotentials for Electronic Structure Theory
- 2021
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:27, s. 15103-15111
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Tidskriftsartikel (refereegranskat)abstract
- We present a general method of constructing in situ pseodopotentials from first-principles, all-electron, and full-potential electronic structure calculations of a solid. The method is applied to bcc Na, at low-temperature equilibrium volume. The essential steps of the method involve (i) calculating an all-electron Kohn-Sham eigenstate, (ii) replacing the oscillating part of the wave function (inside the muffin-tin spheres) of this state, with a smooth function, (iii) representing the smooth wave function in a Fourier series, and (iv) inverting the Kohn-Sham equation, to extract the pseudopotential that produces the state generated in steps i-iii. It is shown that an in situ pseudopotential can reproduce an all-electron full-potential eigenvalue up to the sixth significant digit. A comparison of the all-electron theory, in situ pseudopotential theory, and the standard nonlocal pseudopotential theory demonstrates good agreement, e.g., in the energy dispersion of the 3s band state of bcc Na.
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| 15. |
- Bo, Tao, et al.
(författare)
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Hexagonal Ti2B2 monolayer : a promising anode material offering high rate capability for Li-ion and Na-ion batteries
- 2018
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : ROYAL SOC CHEMISTRY. - 1463-9076 .- 1463-9084. ; 20:34, s. 22168-22178
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Tidskriftsartikel (refereegranskat)abstract
- Combining the first-principles density functional method and crystal structure prediction techniques, we report a series of hexagonal two-dimensional transition metal borides including Sc2B2, Ti2B2, V2B2, Cr2B2, Y2B2, Zr2B2, and Mo2B2. Their dynamic and thermal stabilities are testified by phonon and molecular dynamics simulations. We investigate the potential of the two-dimensional Ti2B2 monolayer as an anode material for Li-ion and Na-ion batteries. The Ti2B2 monolayer possesses high theoretical specific capacities of 456 and 342 mA h g(-1) for Li and Na, respectively. The very high Li/Na diffusivity with an ultralow energy barrier of 0.017/0.008 eV indicates an excellent charge-discharge capability. In addition, good electronic conductivity during the whole lithiation process is found by electronic structure calculations. The very small change in volume after the adsorption of one, two, and three layers of Li and Na ions indicates that the Ti2B2 monolayer is robust. These results highlight the suitability of Ti2B2 monolayer as well as the other two-dimensional transition metal borides as excellent anode materials for both Li-ion and Na-ion batteries.
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| 16. |
- Boeije, M. F. J., et al.
(författare)
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On the phase stability of CaCu5-type compounds
- 2017
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Ingår i: Journal of Alloys and Compounds. - : Elsevier BV. - 0925-8388 .- 1873-4669. ; 722, s. 549-554
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Tidskriftsartikel (refereegranskat)abstract
- We present a hybrid method to inspect the phase stability of compounds having a CaCu5-type crystal structure. This is done using 2D stability plots using the Miedema parameters that are based on the work function and electron density of the constituent elements. Stable compounds are separated from unstable binary compounds, with a probability of 94%. For stable compounds, a linear relation is found, showing a constant ratio of charge transfer and electron density mismatch. DFT calculations show the same trend. Elements from the s, d, f-block are all reliably represented, elements from the p-block are still challenging.
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| 17. |
- Bondarenko, Nina G., et al.
(författare)
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Multi-polaron solutions, nonlocal effects and internal modes in a nonlinear chain
- 2019
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Ingår i: Journal of Physics. - : Institute of Physics (IOP). - 0953-8984 .- 1361-648X. ; 31:41
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Tidskriftsartikel (refereegranskat)abstract
- Multipolaron solutions were studied in the framework of the Holstein one-dimensional molecular crystal model. The study was performed in the continuous limit where the crystal model maps into the nonlinear Schrodinger equation for which a new periodic dnoidal solution was found for the multipolaron system. In addition, the stability of the multi-polaron solutions was examined, and it was found that dnoidal and dnoidal solutions stabilize in different ranges of the parameter space. Moreover, the model was studied under the influence of nonlocal effects and the polaronic dynamics was described in terms of internal solitonic modes.
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| 18. |
- Bondarenko, Nina G., et al.
(författare)
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Spin polaronics : Static and dynamic properties of spin polarons in La-doped CaMnO4
- 2019
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 100:13
-
Tidskriftsartikel (refereegranskat)abstract
- The static and dynamic properties of spin polarons in La-doped CaMnO3 are explored theoretically, by means of an effective low-energy Hamiltonian. All parameters of the effective Hamiltonian are evaluated from first-principles theory. The Hamiltonian is used to investigate the temperature stability as well as the response to an external applied electric field, for spin polarons in bulk, surface, and as single two-dimensional layers. Technically this involves atomistic spin-dynamics simulations in combination with kinetic Monte Carlo simulations. Where a comparison can be made, our simulations exhibit excellent agreement with available experimental data and previous theory. Remarkably, we find that excellent control of the mobility of spin polarons in this material can be achieved, and that the critical parameters deciding this are the temperature and strength of the applied electrical field. We outline different technological implications of spin polarons, and point to spin polaronics as an emerging subfield of nanotechnology. In particular, we demonstrate that it is feasible to write and erase information on an atomic scale, by use of spin polarons in CaMnO3.
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| 19. |
- Borisov, Vladislav, et al.
(författare)
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Heisenberg and anisotropic exchange interactions in magnetic materials with correlated electronic structure and significant spin-orbit coupling
- 2021
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 103:17
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Tidskriftsartikel (refereegranskat)abstract
- The Dzyaloshinskii-Moriya (DM) interaction, as well as symmetric anisotropic exchange, are important ingredients for stabilizing topologically nontrivial magnetic textures, such as, e.g., skyrmions, merons, and hopfions. These types of textures are currently in focus from a fundamental science perspective and they are also discussed in the context of future spintronics information technology. While the theoretical understanding of the Heisenberg exchange interactions is well developed, it is still a challenge to access, from first principles theory, the DM interaction as well as the symmetric anisotropic exchange, which both require a fully-relativistic treatment of the electronic structure, in magnetic systems where substantial electron-electron correlations are present. Here, we present results of a theoretical framework which allows to compute these interactions in any given system and demonstrate its performance for several selected cases, for both bulk and low-dimensional systems. We address several representative cases, including the bulk systems CoPt and FePt, the B20 compounds MnSi and FeGe as well as the low-dimensional transition metal bilayers Co/Pt(111) andMn/W(001). The effect of electron-electron correlations is analyzed using dynamical mean-field theory on the level of the spin-polarized T -matrix + fluctuating exchange (SPTF) approximation, as regards the strength and character of the isotropic (Heisenberg) and anisotropic (DM) interactions in relation to the underlying electronic structure. Our method can be combined with more advanced techniques for treating correlations, e.g., quantum Monte Carlo and exact diagonalization methods for the impurity solver of dynamical mean-field theory. We find that correlation-induced changes of the DM interaction can be rather significant, with up to fivefold modifications in the most distinctive case.
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| 20. |
- Borisov, Vladislav, et al.
(författare)
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Tuning skyrmions in B20 compounds by 4d and 5d doping
- 2022
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Ingår i: Physical Review Materials. - : American Physical Society (APS). - 2475-9953. ; 6:8
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Tidskriftsartikel (refereegranskat)abstract
- Skyrmion stabilization in novel magnetic systems with the B20 crystal structure is reported here, primarily based on theoretical results. The focus is on the effect of alloying on the 3d sublattice of the B20 structure by substitution of heavier 4d and 5d elements, with the ambition to tune the spin-orbit coupling and its influence on magnetic interactions. State-of-the-art methods based on density functional theory are used to calculate both isotropic and anisotropic exchange interactions. Significant enhancement of the Dzyaloshinskii-Moriya interaction is reported for 5d-doped FeSi and CoSi, accompanied by a large modification of the spin stiffness and spiralization. Micromagnetic simulations coupled to atomistic spin-dynamics and ab initio magnetic interactions reveal the spin-spiral nature of the magnetic ground state and field-induced skyrmions for all these systems. Especially small skyrmions similar to 50 nm are predicted for Co0.75Os0.25Si, compared to similar to 148 nm for Fe0.75Co0.25Si. Convex-hull analysis suggests that all B20 compounds considered here are structurally stable at elevated temperatures and should be possible to synthesize. This prediction is confirmed experimentally by synthesis and structural analysis of the Ru-doped CoSi systems discussed here, both in powder and in single-crystal forms.
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| 21. |
- Brumboiu, Iulia, et al.
(författare)
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Atomic photoionization cross sections beyond the electric dipole approximation
- 2019
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Ingår i: Journal of Chemical Physics. - : AMER INST PHYSICS. - 0021-9606 .- 1089-7690. ; 150:4
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Tidskriftsartikel (refereegranskat)abstract
- A methodology is developed to compute photoionization cross sections beyond the electric dipole approximation from response theory, using Gaussian type orbitals and plane waves for the initial and final states, respectively. The methodology is applied to compute photoionization cross sections of atoms and ions from the first four rows of the periodic table. Analyzing the error due to the plane wave description of the photoelectron, we find kinetic energy and concomitant photon energy thresholds above which the plane wave approximation becomes applicable. The correction introduced by going beyond the electric dipole approximation increases with photon energy and depends on the spatial extension of the initial state. In general, the corrections are below 10% for most elements, at a photon energy reaching up to 12 keV. 2019 Author(s).
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| 22. |
- Brumboiu, Iulia Emilia, et al.
(författare)
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Photoelectron Spectroscopy of Molecules Beyond the Electric Dipole Approximation
- 2019
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Ingår i: Journal of Chemical Theory and Computation. - : AMER CHEMICAL SOC. - 1549-9618 .- 1549-9626. ; 15:10, s. 5483-5494
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Tidskriftsartikel (refereegranskat)abstract
- A methodology implemented to compute photoionization cross sections beyond the electric dipole approximation using Gaussian type orbitals for the initial state and plane waves for the final state is applied to molecules of various sizes. The molecular photoionization cross sections computed for valence molecular orbitals as a function of photon energy present oscillations due to the wave-like nature of both the outgoing photoelectron and of the incoming photon. These oscillations are damped by rotational and vibrational averaging or by performing a k-point summation for the solid state case. For core orbitals, the corrections introduced by going beyond the electric dipole approximation are comparable to the atomic case. For valence orbitals, nondipole corrections to the total photoinization cross sections can reach up to 20% at photon energies above 1 keV. The corrections to the differential cross sections calculated at the magic angle are larger, reaching values between 30% and 50% for all molecules included. Our findings demonstrate that photoelectron spectroscopy, especially angle-resolved, on, e.g., molecules and clusters on surfaces, using high photon energies, must be accompanied by theories that go beyond the electric dipole approximation.
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| 23. |
- Brumboiu, Iulia, et al.
(författare)
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Ligand Effects on the Linear Response Hubbard U : The Case of Transition Metal Phthalocyanines
- 2019
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Ingår i: Journal of Physical Chemistry A. - : AMER CHEMICAL SOC. - 1089-5639 .- 1520-5215. ; 123:14, s. 3214-3222
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Tidskriftsartikel (refereegranskat)abstract
- It is established that density functional theory (DFT) + U is a better choice compared to DFT for describing the correlated electron metal center in organometallics. The value of the Hubbard U parameter may be determined from linear response, either by considering the response of the metal site alone or by additionally considering the response of other sites in the compound. We analyze here in detail the influence of ligand shells of increasing size on the U parameter calculated from the linear response for five transition metal phthalocyanines. We show that the calculated multiple-site U ligand atoms that are mainly responsible for this difference are is larger than the single-site U by as much as 1 eV and the ligand atoms that are mainly responsible for this difference are the isoindole nitrogen atoms directly bonded to the central metal atom. This suggests that a different U value may be required for computations of chemisorbed molecules compared to physisorbed and gas-phase cases.
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| 24. |
- Cardias Alves de Almeida, Ramon, 1990-
(författare)
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Electronic structure and exchange interactions from ab initio theory : New perspectives and implementations
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, the magnetic properties of several materials were investigated using first principle calculations. The ab initio method named real space linear muffin-tin orbitals atomic sphere approximation (RS-LMTO-ASA) was used to calculate the electronic structure and magnetic properties of bulk systems, surface and nanostructures adsorbed on surfaces.We have implemented new features in the RS-LMTO-ASA method, such as the calculation of (a) Bloch Spectral Function (BSF), (b) orbital resolved Jij and (c) Dzyaloshinskii-Moriya interaction (DMI). Using (a), we have shown that one can calculate the dispersion relation for bulk systems using a real space method. Furthermore, the dispersion relation was revealed to be existent even for finite one-dimensional structures, such as the Mn chain on Au(111) and Ag(111) surfaces. With (b), we have investigated the orbital resolved exchange coupling parameter Jij for 3d metals. It is demonstrated that the nearest neighbor (NN) interaction for bcc Fe has intriguing behavior, however, the contribution coming from the T2g orbitals favours the anti-ferromagnetic coupling behavior. Moreover, the Fermi surface for bcc Fe is formed mostly by the T2g orbitals and these are shown to be highly Heisenberg-like, i.e. do not depend significantly on the magnetic configuration. Later, the same approach was used to study other transition metals, such as Cr, Mn, Co and Ni. In the end, we have presented the results obtained with the implementation (c). Our results have shown the large dependence of the DMI values, both the strength and direction, with respect to which magnetic configuration they are calculated from. We argue that, for the investigated systems, the non-collinearity induces currents (spin and charge) that will influence directly the DMI vectors.
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| 25. |
- Cardias, Ramon, et al.
(författare)
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Comment on "Proper and improper chiral magnetic interactions"
- 2022
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Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 105:2
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Tidskriftsartikel (refereegranskat)abstract
- In a recent paper by dos Santos Dias et al. [Phys. Rev. B 103, L140408 (2021)], a critique of earlier works analyzing low-energy spin Hamiltonians is put forth. To be precise, it is the large noncollinear contributions to the Dzyaloshinskii-Moriya interaction (DMI) that is the main concern of dos Santos Dias et al. In this Comment, we clarify the microscopic mechanisms for the large DMI that can be found in noncollinear magnets. Furthermore, we outline the complementary nature of the different parametrizations of a spin Hamiltonian, with strengths and weaknesses of both approaches. Specifically, we stress the physical insight in the interpretation of the DMI, when decomposed in microscopic electron and spin densities and currents.
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| 26. |
- Cardias, Ramon, 1990-, et al.
(författare)
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First-principles Dzyaloshinskii-Moriya interaction in a non-collinear framework
- 2020
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- We have derived an expression of the Dzyaloshinskii-Moriya interaction (DMI), where all the three components of the DMI vector can be calculated independently, for a general, non-collinear magnetic configuration. The formalism is implemented in a real space-linear muffin-tin orbital-atomic sphere approximation (RS-LMTO-ASA) method. We have chosen the Cr triangular trimer on Au(111) and Mn triangular trimers on Ag(111) and Au(111) surfaces as numerical examples. The results show that the DMI (module and direction) is drastically different between collinear and non-collinear states. Based on the relation between the spin and charge currents flowing in the system and their coupling to the non-collinear magnetic configuration of the triangular trimer, we demonstrate that the DMI interaction can be significant, even in the absence of spin-orbit coupling. This is shown to emanate from the non-collinear magnetic structure, that can induce significant spin and charge currents even with spin-orbit coupling is ignored.
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| 27. |
- Cardias, Ramon, 1990-, et al.
(författare)
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First-principles Dzyaloshinskii-Moryia interaction in a non-collinear framework
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Including dierent terms in the spin-Hamiltonian, we have derived an expression for theDzyaloshinskii-Moryia vector interaction (DMI) where all the three components of the vector canbe calculated independently of the magnetic conguration. Here, we have chosen the Cr triangulartrimer on Au(111) and Mn triangular trimes on Ag(111) and Au(111) surfaces to study the implementationof the derived DMI into the RS-LMTO-ASA method. Our results have shown thatthe DMI value (module and direction) is drastically dierent for collinear and non-collinear states.Based on relation between the spin and charge currents owing in the system and the non-collinearmagnetic conguration of the triangular trimer, we argued that the drastic change between the DMIcalculated considering a collinear and a non-collinear magnetic conguration can be explained bythe mechanism behind the spin and charge currents owing through the atoms when the spins arealigned in a non-collinear fashion.
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| 28. |
- Cardias, R., et al.
(författare)
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The Bethe-Slater curve revisited; new insights from electronic structure theory
- 2017
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- The Bethe-Slater (BS) curve describes the relation between the exchange coupling and interatomic distance. Based on a simple argument of orbital overlaps, it successfully predicts the transition from antiferromagnetism to ferromagnetism, when traversing the 3d series. In a previous article [Phys. Rev. Lett. 116, 217202 (2016)] we reported that the dominant nearestneighbour (NN) interaction for 3d metals in the bcc structure indeed follows the BS curve, but the trends through the series showed a richer underlying physics than was initially assumed. The orbital decomposition of the inter-site exchange couplings revealed that various orbitals contribute to the exchange interactions in a highly non-trivial and sometimes competitive way. In this communication we perform a deeper analysis by comparing 3d metals in the bcc and fcc structures. We find that there is no coupling between the E-g orbitals of one atom and T-2g orbitals of its NNs, for both cubic phases. We demonstrate that these couplings are forbidden by symmetry and formulate a general rule allowing to predict when a similar situation is going to happen. In gamma-Fe, as in alpha-Fe, we find a strong competition in the symmetry-resolved orbital contributions and analyse the differences between the high-spin and low-spin solutions.
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| 29. |
- Cardias, Ramon, et al.
(författare)
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Unraveling the connection between high-order magnetic interactions and local-to-global spin Hamiltonian in noncollinear magnetic dimers
- 2023
-
Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 108:22
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Tidskriftsartikel (refereegranskat)abstract
- A spin Hamiltonian that characterizes interatomic interactions between spin moments is highly valuable in predicting and comprehending the magnetic properties of materials. Here, we explore a method for explicitly calculating interatomic exchange interactions in noncollinear configurations of magnetic materials considering only a bilinear spin Hamiltonian in a local scenario. Based on density-functional theory calculations of dimers adsorbed on metallic surfaces, and with a focus on the Dzyaloshinskii-Moriya interaction (DMI) which is essential for stabilizing chiral noncollinear magnetic states, we discuss the interpretation of the DMI when decomposed into microscopic electron and spin densities and currents. We clarify the distinct origins of spin currents induced in the system and their connection to the DMI. In addition, we reveal how noncollinearity affects the usual DMI, which is solely induced by spin-orbit coupling, and DMI-like interactions brought about by noncollinearity. We explain how the dependence of the DMI on the magnetic configuration establishes a connection between high-order magnetic interactions, enabling the transition from a local to a global spin Hamiltonian.
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| 30. |
- Chareev, Dmitriy A., et al.
(författare)
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Stable Sulfuric Vapor Transport and Liquid Sulfur Growth on Transition Metal Dichalcogenides
- 2023
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Ingår i: Crystal Growth & Design. - : ACS Publications. - 1528-7483 .- 1528-7505. ; 23:4, s. 2287-2294
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Tidskriftsartikel (refereegranskat)abstract
- Transition metal dichalcogenides (TMDs) are an emergent class of low-dimensional materials with growing applications in the field of nanoelectronics. However, efficient methods for synthesizing large monocrystals of these systems are still lacking. Here, we describe an efficient synthetic route for a large number of TMDs that were obtained in quartz glass ampoules by sulfuric vapor transport and liquid sulfur. Unlike the sublimation technique, the metal enters the gas phase in the form of molecules, hence containing a greater amount of sulfur than the growing crystal. We have investigated the physical properties for a selection of these crystals and compared them to state-of-the-art findings reported in the literature. The acquired electronic properties features demonstrate the overall high quality of single crystals grown in this work as exemplified by CoS2, ReS2, NbS2, and TaS2. This new approach to synthesize high-quality TMD single crystals can alleviate many material quality concerns and is suitable for emerging electronic devices.
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| 31. |
- Chimata, Raghuveer, et al.
(författare)
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Magnetism and ultrafast magnetization dynamics of Co and CoMn alloys at finite temperature
- 2017
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 95:21
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Tidskriftsartikel (refereegranskat)abstract
- Temperature-dependent magnetic experiments such as pump-probe measurements generated by a pulsed laser have become a crucial technique for switching the magnetization in the picosecond time scale. Apart from having practical implications on the magnetic storage technology, the research field of ultrafast magnetization poses also fundamental physical questions. To correctly describe the time evolution of the atomic magnetic moments under the influence of a temperature-dependent laser pulse, it remains crucial to know if the magnetic material under investigation has magnetic excitation spectrum that is more or less dependent on the magnetic configuration, e.g., as reflected by the temperature dependence of the exchange interactions. In this paper, we demonstrate from first-principles theory that the magnetic excitation spectra in Co in fcc, bcc, and hcp structures are nearly identical in a wide range of noncollinear magnetic configurations. This is a curious result of a balance between the size of the magnetic moments and the strength of the Heisenberg exchange interactions, that in themselves vary with configuration, but put together in an effective spin Hamiltonian results in a configuration-independent effective model. We have used such a Hamiltonian, together with ab initio calculated damping parameters, to investigate the magnon dispersion relationship as well as ultrafast magnetization dynamics of Co and Co-rich CoMn alloys.
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| 32. |
- Dalin, Frida, 1984-, et al.
(författare)
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Clinical and immunological characteristics of Autoimmune Addison's disease : a nationwide Swedish multicenter study
- 2017
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Ingår i: Journal of Clinical Endocrinology and Metabolism. - : Oxford University Press. - 0021-972X .- 1945-7197. ; 102:2, s. 379-389
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Tidskriftsartikel (refereegranskat)abstract
- CONTEXT: Studies on clinical and immunological features of Autoimmune Addison's disease (AAD) are needed to understand the disease burden and increased mortality.OBJECTIVE: To provide upgraded data on autoimmune comorbidities, replacement therapy, autoantibody profiles and cardiovascular risk factors.DESIGN, SETTING AND PARTICIPANTS: Cross sectional, population-based study. 660 AAD patients were included utilizing the Swedish Addison Registry (SAR) 2008-2014. When analyzing cardiovascular risk factors, 3,594 individuals from the population-based survey in Northern Sweden, MONICA (MONItoring of Trends and Determinants of CArdiovascular Disease), served as controls.MAIN OUTCOME MEASURE: Prevalence of autoimmune comorbidities and cardiovascular risk factors. Autoantibodies against 13 autoantigens were determined.RESULTS: Sixty percent of the SAR cohort consisted of females. Mean age at diagnosis was significantly higher for females than for males (36.8 vs. 31.1 years). The proportion of 21-hydroxylase autoantibody positive patients was 83% and 62% of patients had one or more associated autoimmune diseases, more frequently coexisting in females (p<0.0001). AAD patients had lower BMI (p<0.0001) and prevalence of hypertension (p=0.027) compared with controls. Conventional hydrocortisone tablets were used by 89% of patients; with the mean dose 28.1±8.5 mg/day. The mean hydrocortisone equivalent dose normalized to body surface was 14.8±4.4 mg/m(2)/day. Higher hydrocortisone equivalent dose was associated with higher incidence of hypertension (p=0.046).CONCLUSIONS: Careful monitoring of AAD patients is warranted to detect associated autoimmune diseases. Contemporary Swedish AAD patients do not have increased prevalence of overweight, hypertension, T2DM or hyperlipidemia. However, high glucocorticoid replacement doses may be a risk factor for hypertension.
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| 33. |
- Dan, Tinku, et al.
(författare)
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Local structural evolution in the anionic solid solution ZnSexS1-x
- 2021
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Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:18
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Tidskriftsartikel (refereegranskat)abstract
- The century-old Vegard's law has been remarkably accurate in describing the evolution of the lattice parameters of almost all solid solutions. Contractions or expansions of lattice parameters of such systems depend on the size of the guest atom being smaller or larger than the host atom it replaces to form the solid solution. This has given rise to the concept of "chemical pressure" in analogy to the physical pressure. We have investigated using EXAFS the evolution of the local structure in terms of atom-pair distances extending up to the third-nearest neighbors in the family of compounds, ZnSexS1-x as an example of an anionic solid solution, in contrast to all previous studies focusing on cationic solid solutions. Our results establish several common features between these two types of solid solutions, while strongly suggesting that the concept of a chemical pressure is inaccurate and misleading. Most interestingly, we also find a qualitative difference between the cationic solid solutions, reported earlier, and the anionic solid solution.
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| 34. |
- Dastanpour Hosseinabadi, Esmat, et al.
(författare)
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Investigation of the metastable spinodally decomposed magnetic CrFe-rich phase in Al doped CrFeCoNi alloy
- 2023
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 939
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Tidskriftsartikel (refereegranskat)abstract
- We have conducted an in-depth study of the magnetic phase due to a spinodal decomposition of the BCC phase of a CrFe-rich composition. This magnetic phase is present after casting (arc melting) or water quenching after annealing at 1250 degrees C for 24 h but is entirely absent after annealing in the interval 900-1100 degrees C for 24 h. Its formation is favored in the temperature interval ca 450-550 degrees C and loses magnetization above 640 degrees C. This ferromagnetic-paramagnetic transition is due to a structural transformation from ferromagnetic BCC into paramagnetic sigma and FCC phases. The conclusion from measurements at different heating rates is that both the transformation leading to the increase of the magnetization due to the spinodal decomposition of the parent phase and the vanishing magnetization at 640 degrees C are diffusion controlled. (c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).
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| 35. |
- Dastanpour Hosseinabadi, Esmat, et al.
(författare)
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On the structural and magnetic properties of Al-rich high entropy alloys : a joint experimental-theoretical study
- 2023
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 56:1
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Tidskriftsartikel (refereegranskat)abstract
- The present work investigates how the vanadium (V) content in a series of Al50V (x) (Cr0.33Mn0.33Co0.33)((50-x)) (x = 12.5, 6.5, 3.5, and 0.5 at.%) high-entropy alloys affects the local magnetic moment and magnetic transition temperature as a step towards developing high-entropy functional materials for magnetic refrigeration. This has been achieved by carrying out experimental investigations on induction melted alloys and comparison to ab initio and thermodynamic calculations. Structural characterization by x-ray diffraction and scanning electron microscopy indicates a dual-phase microstructure containing a disordered body-centered cubic (BCC) phase and a B2 phase with long-range order, which significantly differ in the Co and V contents. Ab initio calculations demonstrate a weaker magnetization and lower magnetic transition temperature (T
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| 36. |
- Dong, Zhihua, et al.
(författare)
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MnxCr0.3Fe0.5Co0.2Ni0.5Al0.3 high entropy alloys for magnetocaloric refrigeration near room temperature
- 2021
-
Ingår i: Journal of Materials Science & Technology. - : Chinese Society of Metals. - 1005-0302. ; 79, s. 15-20
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Tidskriftsartikel (refereegranskat)abstract
- High entropy alloys (HEAs) based on transition metals display rich magnetic characteristics, however attempts on their application in energy efficient technologies remain scarce. Here, we explore the magnetocaloric application for a series of MnxCr0.3Fe0.5Co0.2Ni0.5Al0.3 (0.8 < x < 1.1) HEAs by integrated theoretical and experimental methods. Both theory and experiment indicate the designed HEAs have the Curie temperature close to room temperature and is tunable with Mn concentration. A non-monotonic evolution is observed for both the entropy change and the relative cooling power with changing Mn concentration. The underlying atomic mechanism is found to primarily emerge from the complex impact of Mn on magnetism. Advanced magnetocaloric properties can be achieved by tuning Mn concentration in combination with controlling structural phase stability for the designed HEAs.
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| 37. |
- Elhanoty, Mohamed F., et al.
(författare)
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Different fingerprints for the OISTR mechanism in the magnetic alloys experiments
- 2022
-
Ingår i: ADVANCES IN ULTRAFAST CONDENSED PHASE PHYSICS III. - : SPIE - The International Society for Optics and Photonics. - 9781510651418 - 9781510651401
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Konferensbidrag (refereegranskat)abstract
- The interplay between various degrees of freedom in laser induced ultrafast magnetization dynamics (LIUMD) of magnetic alloys is intricate due to the competition between different mechanisms and processes. In this work, we resolve the element specific magnetization dynamics of FePd alloy and further elucidate the dependency of the OISTR mechanism on the laser pulse parameters using ultrashort, short and relatively longer pulse duration with weak and strong fluence. Remarkably, our results illustrate potential discrepancies in experiments measuring the optical inter site spin transfer (OISTR) effect in magnetic alloys.
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| 38. |
- Elhanoty, Mohamed F., et al.
(författare)
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Element-selective ultrafast magnetization dynamics of hybrid Stoner-Heisenberg magnets
- 2022
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 105:10
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Tidskriftsartikel (refereegranskat)abstract
- Stoner and Heisenberg excitations in magnetic materials are inherently different. The first involves an effective reduction of the exchange splitting, whereas the second comprises excitation of spin waves. In this work, we test the impact of these two excitations in the hybrid Stoner-Heisenberg system of FePd. We present a microscopic picture of ultrafast demagnetization dynamics in this alloy, which represents both components of strong local exchange splitting in Fe and induced polarization in Pd. We identify the spin-orbit coupling (SOC) and the optical intersite spin transfer (OISTR) as the two dominant factors for demagnetization at ultrashort timescales. Remarkably, the drastic difference in the origin of the magnetic moment of the Fe and Pd species is not deciding the initial magnetization dynamics in this alloy. By tuning the external laser pulse, the extrinsic OISTR can be manipulated for site-selective demagnetization on femtosecond timescales providing the fastest way for optical and selective control of the magnetization dynamics in alloys. Saliently, our results signify why various experiments demonstrating OISTR might obtain conflicting results.
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| 39. |
- Eriksson, Martin, et al.
(författare)
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SAS and the Cold War
- 2023
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Ingår i: 15th Swedish Economic History Meeting.
-
Konferensbidrag (refereegranskat)
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| 40. |
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| 41. |
- George, Sebastian, 1990-, et al.
(författare)
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Local structure in amorphous SmxCo1-x : a combined experimental and theoretical study
- 2020
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 55, s. 12488-12498
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Tidskriftsartikel (refereegranskat)abstract
- Using a combination of extended X-ray absorption fine structure measurements, stochastic quenching (SQ) calculations and Voronoi tessellation analysis, the local atomic environments in thin films of amorphous SmxCo1−x (x= 0.10, 0.22 and 0.35) are investigated and also compared with crystalline stoichiometric Sm–Co alloys of similar compositions. It is found that the variations in local environment around Co atoms in the amorphous films increase with increasing x and that none of the films exhibit any pronounced short-range order around the Sm atoms. There are, however, signs of clustering of Sm atoms in the SQ-generated simulated amorphous materials. Furthermore, good agreement is observed between experimentally obtained parameters, e.g., interatomic distances and coordination numbers, and those extracted from the simulated alloys. This is a strong indication that SQ provides a powerful route to reliable local structure information for amorphous rare earth–transition metal alloys and that it could be used for designing materials with properties that meet the demands of specific applications.
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| 42. |
- Ghorai, Sagar, et al.
(författare)
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Giant magnetocaloric effect in the (Mn,Fe)NiSi-system
- 2023
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The search for energy-efficient and environmentally friendly cooling technologies is a key driver for the development of magnetic refrigeration based on the magnetocaloric effect (MCE). This phenomenon arises from the interplay between magnetic and lattice degrees of freedom that is strong in certain materials, leading to a change in temperature upon application or removal of a magnetic field. Here we report on a new material, Mn1−xFexNiSi0.95Al0.05, with an exceptionally large isothermal entropy at room temperature. By combining experimental and theoretical methods we outline the microscopic mechanism behind the large MCE in this material. It is demonstrated that the competition between the Ni2In-type hexagonal phase and the MnNiSi-type orthorhombic phase, that coexist in this system, combined with the distinctly different magnetic properties of these phases, is a key parameter for the functionality of this material for magnetic cooling.
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| 43. |
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| 44. |
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| 45. |
- Ghorai, Sagar, et al.
(författare)
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Site-specific atomic substitution in a giant magnetocaloric Fe2P-type system
- 2023
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 107:10
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Tidskriftsartikel (refereegranskat)abstract
- Giant magnetocaloric (GMC) materials constitute a requirement for near room temperature magnetic refrigeration. (Fe,Mn)2(P,Si) is a GMC compound with strong magnetoelastic coupling. The main hindrance towards application of this material is a comparably large temperature hysteresis, which can be reduced by metal site substitution with a nonmagnetic element. However, the (Fe,Mn)2(P,Si) compound has two equally populated metal sites, the tetrahedrally coordinated 3f and the pyramidally coordinated 3g sites. The magnetic and magnetocaloric properties of such compounds are highly sensitive to the site specific occupancy of the magnetic atoms. Here we have attempted to study separately the effect of 3f and 3g site substitution with equal amounts of vanadium. Using formation energy calculations, the site preference of vanadium and its influence on the magnetic phase formation are described. A large difference in the isothermal entropy change (as high as 44\%) with substitution in the 3f and 3g sites is observed. The role of the lattice parameter change with temperature and the strength of the magnetoelastic coupling on the magnetic properties are highlighted.
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| 46. |
- Ghosh, Anirudha, et al.
(författare)
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Exotic magnetic and electronic properties of layered CrI3 single crystals under high pressure
- 2022
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 105:8
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Tidskriftsartikel (refereegranskat)abstract
- Through advanced experimental techniques on CrI3 single crystals, we derive a pressure-temperature phase diagram. We find that T-c increases to similar to 66 K with pressure up to similar to 3 GPa followed by a decrease to similar to 10 K at 21.2 GPa. The experimental results are reproduced by theoretical calculations based on density functional theory where electron-electron interactions are treated by a static on-site Hubbard U on Cr 3d orbitals. The origin of the pressure-induced reduction of the ordering temperature is associated with a decrease in the calculated bond angle, from 95 degrees at ambient pressure to similar to 85 degrees at 25 GPa. Above 22 GPa, experiment and theory jointly point to the idea that the ferromagnetically ordered state is destroyed, giving rise first to a complex, unknown magnetic configuration, and at sufficiently high pressures a pure antiferromagnetic configuration. This sequence of transitions in the magnetism is accompanied by a well-detected pressure-induced semiconductor-to-metal phase transition that is revealed by both high-pressure resistivity measurements and ab initio theory.
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| 47. |
- Ghosh, Anirudha, et al.
(författare)
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Magnetic circular dichroism in the dd excitation in the van der Waals magnet CrI3 probed by resonant inelastic x-ray scattering
- 2023
-
Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 107:11
-
Tidskriftsartikel (refereegranskat)abstract
- We report on a combined experimental and theoretical study on CrI3 single crystals by employing the polarization dependence of resonant inelastic x-ray scattering (RIXS). Our investigations reveal multiple Cr 3d orbital splitting (dd excitations) as well as magnetic dichroism (MD) in the RIXS spectra. The dd excitation energies are similar on the two sides of the ferromagnetic transition temperature, T-C similar to 61 K, although MD in RIXS is predominant at 0.4 T magnetic field below TC. This demonstrates that the ferromagnetic superexchange interaction that is responsible for the interatomic exchange field is vanishingly small compared with the local exchange field that comes from exchange and correlation interaction among the interacting Cr 3d orbitals. The recorded RIXS spectra reported here reveal clearly resolved Cr 3d intraorbital dd excitations that represent transitions between electronic levels that are heavily influenced by dynamic correlations and multiconfiguration effects. Our calculations taking into account the Cr 3d hybridization with the ligand valence states and the full multiplet structure due to intra-atomic and crystal field interactions in Oh and D3d symmetry clearly reproduced the dichroic trend in experimental RIXS spectra.
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| 48. |
- Grånäs, Oscar, 1979-, et al.
(författare)
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Ultrafast modification of the electronic structure of a correlated insulator
- 2022
-
Ingår i: Physical Review Research. - : American Physical Society. - 2643-1564. ; 4:3
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Tidskriftsartikel (refereegranskat)abstract
- A nontrivial balance between Coulomb repulsion and kinematic effects determines the electronic structure of correlated electron materials. The use of electromagnetic fields strong enough to rival these native microscopic interactions allows us to study the electronic response as well as the time scales and energies involved in using quantum effects for possible applications. We use element-specific transient x-ray absorption spectroscopy and high-harmonic generation to measure the response to ultrashort off-resonant optical fields in the prototypical correlated electron insulator NiO. Surprisingly, fields of up to 0.22 V/angstrom lead to no detectable changes in the correlated Ni 3d orbitals contrary to previous predictions. A transient directional charge transfer is uncovered, a behavior that is captured by first-principles theory. Our results highlight the importance of retardation effects in electronic screening and pinpoints a key challenge in functionalizing correlated materials for ultrafast device operation.
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| 49. |
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| 50. |
- Gustafsson, Mats, 1966-, et al.
(författare)
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Indikativ metod för bedömning av partikelemission från dubbdäcksslitage av vägbeläggning : modifiering och utvärdering av Tröger-metoden
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Att testa partikelemissionen från dubbdäcksslitage av vägbeläggningar på ett kontrollerat sätt är oftast förknippat med verklighetsnära, men storskaliga tester med storskalig och avancerad laboratorie[1]utrustning och därmed förhållandevis höga kostnader. Det finns därför ett angeläget behov av en enklare metod som kan användas för att ge en rimlig och god skattning av hur skillnader i beläggningsrecept påverkar partikelbildningen, som kan användas till val av beläggningsrecept som ska användas i senare storskaliga tester. En möjlighet är att använda en befintlig slitagetestmetod för provkroppar av slitlager. Tröger är en sådan metod där ett knippe stålnålar hamrar mot en roterande provkropp i ett klimatskåp som bedömds lämplig för att mäta och studera partikelemissioner till luft. VTI:s Tröger-utrustning modifierades för partikelemissionsmätningar genom att installera partikelinsugsmunstycke i kylluftflödet som passerar över provkroppen. Initiala tester tydde på acceptabel/tillräcklig god repeterbarhet och ett antal provkroppar från några befintliga material med olika slitstyrka valdes ut för vidare tester. En statistiskt optimerad försökplan och provhantering togs fram. En testomgång var planerad initialt men senare utökades det till två omgångar. En andra omgång krävdes dels på grund av att ett material i första omgången misstagits för enhetligt, men bestod av tre olika material, dels då försöksuppställningen kunnat förbättras något. De bildade partiklarna (PM10) har en bimodal fördelning med en primär topp vid 2–3 µm och en sekundär vid ca 8–10 µm. Den statistiska analysen visade på signifikanta skillnader mellan de tre ingående materialen i provkropparna i den andra testomgången och att metoden i sin nuvarande form kan användas för att skilja partikelemissionen från olika vägbeläggningar. Förslag för att utveckla metoden är bland annat att förhindra uppbyggnad av damm i kylsystemet och säkerställa jämn kvalitet hos nålarna.
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