| 1. |
- Jana, Somnath, et al.
(författare)
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Analysis of the linear relationship between asymmetry and magnetic moment at the M edge of 3d transition metals
- 2020
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Ingår i: Physical Review Research. - : American Physical Society. - 2643-1564. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- The magneto-optical response of Fe and Ni during ultrafast demagnetization is studied experimentally and theoretically. We have performed pump-probe experiments in the transverse magneto-optical Kerr effect (T-MOKE) geometry using photon energies that cover the M absorption edges of Fe and Ni between 40 and 72 eV. The magnetic asymmetry was obtained by forming the difference of reflected intensities obtained for two opposite orientations of the sample magnetization. Density functional theory (DFT) was used to calculate the magneto-optical response of different magnetic configurations, representing different types of excitations: long wavelength magnons, short wavelength magnons, and Stoner excitations. In the case of Fe, we find that the calculated asymmetry is strongly dependent on the specific type of magnetic excitation. Our modeling also reveals that during remagnetization Fe is, to a reasonable approximation, described by magnons, even though small nonlinear contributions could indicate some degree of Stoner excitations as well. In contrast, we find that the calculated asymmetry in Ni is rather insensitive to the type of magnetic excitations. However, there is a weak nonlinearity in the relation between asymmetry and the off-diagonal component of the dielectric tensor, which does not originate from the modifications of the electronic structure. Our experimental and theoretical results thus emphasize the need to consider a coupling between asymmetry and magnetization that may be more complex than a simple linear relationship. This insight is crucial for the microscopic interpretation of ultrafast magnetization experiments.
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| 2. |
- Jana, Somnath, et al.
(författare)
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Atom-specific magnon driven ultrafast spin dynamics in Fe1-xNix alloys
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- By employing element specific ultrafast spectroscopy in Fe1-xNix alloys alloys, we find a composition dependent effect in the demagnetization that we relate to changes in electron-magnon scattering. In all six measured alloys of different composition, the demagnetization of Ni compared to Fe exhibits a delay, an effect which we find is inherent in alloys but not in elemental Fe and Ni. Using a model based on electron-magnon scattering, we extract a spin-wave stiffness from all alloys that show excellent agreement with values obtained from other techniques. The result establishes the atom-specific sd-exchange induced magnon generation as an underlying mechanism during ultrafast demagnetization in Fe1-xNix alloys
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| 3. |
- Jana, Somnath, et al.
(författare)
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Atom-specific magnon-driven ultrafast spin dynamics in Fe1-xNix alloys
- 2023
-
Ingår i: Physical Review B. - : American Physical Society (APS). - 2469-9950 .- 2469-9969. ; 107:18
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Tidskriftsartikel (refereegranskat)abstract
- By employing element-specific spectroscopy in the ultrafast time scale in Fe1-xNix alloys, we find a composition-dependent effect in the demagnetization that we relate to electron-magnon scattering and changes in the spin-wave stiffness. In all six measured alloys of different composition, the demagnetization of Ni compared to Fe exhibits a delay, an effect which we find is inherent in alloys but not in elemental Fe and Ni. Using a model based on electron-magnon scattering, we extract a spin-wave stiffness from all alloys that show excellent agreement with values obtained from other techniques.
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| 4. |
- Locht, Inka L. M., 1986-, et al.
(författare)
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Magnetic asymmetry around the 3p absorption edge in Fe and Ni
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This work is a joint theoretical and experimental study of the relation between the magneto- optical response of a material in the sub-picosecond timescale and its instantaneous magnetisation. We perform pump-probe experiments in the transverse magneto-optical Kerr effect (T-MOKE) geometry. We measure the magnetic asymmetry of elemental Fe and Ni before and after the laser pulse. The observed differences between the magnetic asymmetry curves for various photon energies suggest that the relation between asymmetry and sample magnetization is more complex than a simple proportionality. Further insight is obtained by means of theoretical simulations based on density-functional theory. Our calculations show that non-linear effects in the asymmetry are most prominent at energies corresponding to the absorption edge and that the proportionality is recovered outside of this region. In conclusion, our experimental and theoretical results emphasize the need of including the complex relation between asymmetry and magnetization in the interpretation of ultrafast magnetization experiments in terms of microscopic properties.
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| 5. |
- Alagia, M, et al.
(författare)
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Angular effects in autoionization of 3 P doubly excited states in He
- 2009
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Ingår i: Journal of Physics: Conference Series. ; 194
-
Tidskriftsartikel (refereegranskat)abstract
- The first members of dipole allowed 3 P o doubly excited series in helium have been observed in resonant photoexcitation of 1 s 2 s 3 S e metastable atoms. A good agreement measured relative photoionization cross sections is achieved when theory includes the radiation damping and, also important, the effects of spin-orbit multiplet splitting on electron angular distribution.
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| 6. |
- Alagia, M., et al.
(författare)
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Excitation of 1S and 3S Metastable Helium Atoms to Doubly Excited States
- 2009
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 102:15, s. 153001-
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Tidskriftsartikel (refereegranskat)abstract
- We present spectra of triplet and singlet metastable helium atoms resonantly photoexcited to doubly excited states. The first members of three dipole-allowed 1,3Po series have been observed and their relative photoionization cross sections determined, both in the triplet (from 1s2s 3Se) and singlet (from 1s2s 1Se) manifolds. The intensity ratios are drastically different with respect to transitions from the ground state. When radiation damping is included the results for the singlets are in agreement with theory, while for triplets spin-orbit interaction must also be taken into account.
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| 7. |
- Berholts, Marta, et al.
(författare)
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Quantum watch and its intrinsic proof of accuracy
- 2022
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Ingår i: Physical Review Research. - : American Physical Society. - 2643-1564. ; 4:4
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the rich dynamics of complex wave packets composed of multiple high-lying Rydbergstates in He. A quantitative agreement is found between theory and time-resolved photoelectron spectroscopyexperiments. We show that the intricate time dependence of such wave packets can be used for investigatingquantum defects and performing artifact-free timekeeping. The latter relies on the unique fingerprint that iscreated by the time-dependent photoionization of these complex wave packets. These fingerprints determinehow much time has passed since the wave packet was formed and provide an assurance that the measured time iscorrect. Unlike any other clock, this quantum watch does not utilize a counter and is fully quantum mechanicalin its nature. The quantum watch has the potential to become an invaluable tool in pump-probe spectroscopy dueto its simplicity, assurance of accuracy, and ability to provide an absolute timestamp, i.e., there is no need to findtime zero.
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| 8. |
- Couto, Rafael Carvalho, et al.
(författare)
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Breaking inversion symmetry by protonation : Experimental and theoretical NEXAFS study of the diazynium ion, N2H
- 2021
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 23:32, s. 17166-17176
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Tidskriftsartikel (refereegranskat)abstract
- As an example of symmetry breaking in NEXAFS spectra of protonated species we present a high resolution NEXAFS spectrum of protonated dinitrogen, the diazynium ion N2H+. By ab initio calculations we show that the spectrum consists of a superposition of two nitrogen 1s absorption spectra, each including a π∗ band, and a nitrogen 1s to H+ charge transfer band followed by a weak irregular progression of high energy excitations. Calculations also show that, as an effect of symmetry breaking by protonation, the π∗ transitions are separated by 0.23 eV, only slightly exceeding the difference in the corresponding dark (symmetry forbidden) and bright (symmetry allowed) core excitations of neutral N2. By DFT and calculations and vibrational analysis, the complex π∗ excitation band of N2H+ is understood as due to the superposition of the significantly different vibrational progressions of excitations from terminal and central nitrogen atoms, both leading to bent final state geometries. We also show computationally that the electronic structure of the charge transfer excitation smoothly depends on the nitrogen-proton distance and that there is a clear extension of the spectra going from infinity to close nitrogen-proton distance where fine structures show some, although not fully detailed, similarities. An interesting feature of partial localization of the nitrogen core orbitals, with a strong, non-monotonous, variation with nitrogen-proton distance could be highlighted. Specific effects could be unraveled when comparing molecular cation NEXAFS spectra, as represented by recently recorded spectra of N2+ and CO+, and spectra of protonated molecules as represented here by the N2H+ ion. Both types containing rich physical effects not represented in NEXAFS of neutral molecules because of the positive charge, whereas protonation also breaks the symmetry. The effect of the protonation on dinitrogen can be separated in charge, which extends the high-energy part of the spectrum, and symmetry-breaking, which is most clearly seen in the low-energy π∗ transition.
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| 9. |
- Couto, Rafael Carvalho, et al.
(författare)
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The carbon and oxygen K-edge NEXAFS spectra of CO
- 2020
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 22:28, s. 16215-16223
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Tidskriftsartikel (refereegranskat)abstract
- We present and analyze high resolution near edge X-ray absorption fine structure (NEXAFS) spectra of CO+ at the carbon and oxygen K-edges. The spectra show a wealth of features that appear very differently at the two K-edges. The analysis of these features can be divided into three parts; (i) repopulation transition to the open shell orbital – here the C(1s) or O(1s) to 5σ transition, where the normal core hole state is reached from a different initial state and different interaction than in X-ray photoelectron spectroscopy; (ii) spin coupled split valence bands corresponding to C(1s) or O(1s) to π* transitions; (iii) remainder weak and long progressions towards the double ionization potentials containing a manifold of peaks. These parts, none of which has correspondence in NEXAFS spectra of neutral molecules, are dictated by the localization of the singly occupied 5σ orbital, adding a dimension of chemistry to the ionic NEXAFS technique.
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| 10. |
- Eichmann, U., et al.
(författare)
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Photon-recoil imaging : Expanding the view of nonlinear x-ray physics
- 2020
-
Ingår i: Science. - : AMER ASSOC ADVANCEMENT SCIENCE. - 0036-8075 .- 1095-9203. ; 369:6511, s. 1630-1633
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Tidskriftsartikel (refereegranskat)abstract
- Addressing the ultrafast coherent evolution of electronic wave functions has long been a goal of nonlinear x-ray physics. A first step toward this goal is the investigation of stimulated x-ray Raman scattering (SXRS) using intense pulses from an x-ray free-electron laser. Earlier SXRS experiments relied on signal amplification during pulse propagation through dense resonant media. By contrast, our method reveals the fundamental process in which photons from the primary radiation source directly interact with a single atom. We introduce an experimental protocol in which scattered neutral atoms rather than scattered photons are detected. We present SXRS measurements at the neon K edge and a quantitative theoretical analysis. The method should become a powerful tool in the exploration of nonlinear x-ray physics.
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| 11. |
- 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
-
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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| 12. |
- Guo, J. -H, et al.
(författare)
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Electronic structure study of the bases in DNA duplexes by in situ photon-in/photon-out soft X-ray spectroscopy
- 2010
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier BV. - 0368-2048 .- 1873-2526. ; 181:2-3, s. 197-201
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Tidskriftsartikel (refereegranskat)abstract
- Understanding protein functionality is of fundamental importance in biochemistry. Soft X-ray transitions, where the core-level vacancies are filled by the valence-orbital electrons, give direct information about the chemical bonding. Soft X-ray absorption and emission study of poly(dG) -poly(dC) in aqueous solutions can elucidate the relation between the structure and functionality of proteins. We report the N K-edge soft X-ray absorption (XAS) and resonant soft X-ray emission spectroscopy (XES) to characterize the electronic structure near the Fermi level of DNA duplexes to specify the charge migration mechanism. Since N atoms are included in only bases in DNA duplexes, the XES spectra excited from N Is to unoccupied states purely extract the electronic orbital features of the bases in DNA. The fact that N atoms in different bonding environments form well-defined structure has been determined. The experimental findings provide the evidence for the charge-hopping and/or charge-transfer effects in understanding of electric conduction in DNA duplexes when electrons pass through the pi* states of DNA bases.
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| 13. |
- Jana, Somnath, et al.
(författare)
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A setup for element specific magnetization dynamics using the transverse magneto-optic Kerr effect in the energy range of 30-72 eV
- 2017
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Ingår i: Review of Scientific Instruments. - : AMER INST PHYSICS. - 0034-6748 .- 1089-7623. ; 88:3
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we present a spectrometer that is designed for element-specific and time-resolved transverse magneto-optic Kerr effect experiments at the high-harmonic generation pump-probe facility High Energy Laser Induced Overtone Source (HELIOS) laboratory. HELIOS delivers photons with energies between 30 eV and 72 eV with an overall time resolution of less than 40 fs. The spectrometer is based on a Rowland-circle geometry and allows for simultaneous measurements of all magnetic transition-metal elements. The setup also features easy sample transfer and alignment, and it combines high photon throughput, optimized data acquisition, and a fast switching of the magnetic field at the sample. The spectrometer performance is demonstrated by measuring the ultrafast demagnetization of permalloy. Our data are, for all practical purposes, identical to what have been reported in the earlier high-order harmonic generation work of a similar sample by Mathias et al. [Proc. Natl. Acad. Sci. U.S.A. 109, 4792-4797 (2012)], however, obtained within 15% of the acquisition time compared to their study. Furthermore, our data show a shift of the demagnetization curve of Ni relative to Fe, which has previously been interpreted as a delay of the Ni demagnetization to that of Fe [S. Mathias et al., Proc. Natl. Acad. Sci. U. S. A. 109, 4792-4797 (2012)].
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| 14. |
- Kaiser, L., et al.
(författare)
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Angular emission distribution of O 1s photoelectrons of uniaxially oriented methanol
- 2020
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Ingår i: Journal of Physics B. - : IOP Publishing. - 0953-4075 .- 1361-6455. ; 53:19
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Tidskriftsartikel (refereegranskat)abstract
- The angular distribution of O 1s photoelectrons emitted from uniaxially oriented methanol is studied experimentally and theoretically. We employed circularly polarized photons of an energy ofh nu= 550 eV for our investigations. We measured the three-dimensional photoelectron angular distributions of methanol, with the CH3-OH axis oriented in the polarization plane, by means of cold target recoil ion momentum spectroscopy. The experimental results are interpreted by single active electron calculations performed with the single center method. A comparative theoretical study of the respective molecular-frame angular distributions of O 1s photoelectrons of CO, performed for the same photoelectron kinetic energy and for a set of different internuclear distances, allows for disentangling the role of internuclear distance and the hydrogen atoms of methanol as compared to carbon monoxide.
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| 15. |
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| 16. |
- Liu, H., et al.
(författare)
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Optical and extreme UV studies of spin dynamics in metallic and insulating ferrimagnets
- 2021
-
Ingår i: Journal of Applied Physics. - : American Institute of Physics (AIP). - 0021-8979 .- 1089-7550. ; 130:24
-
Tidskriftsartikel (refereegranskat)abstract
- We present all-optical studies of spin dynamics in two classes of ferrimagnets. Both sets of experiments use table-top laser-based pump–probe techniques to examine the ultrafast and longer timescale spin excitations. We use the visible/near infra-red time-resolved magneto-optical Kerr effect (tr-MOKE) to follow the spin dynamics of a series of metallic (FeCo)1−xGdx thin films with varying Gd content. Magnetic compensation in the films occurs at a Gd concentration of ≈26%, and the spin dynamics of the films exhibit a non-monotonic variation in effective magnetization. We also examine spin dynamics in an insulating NiFe2O4 spinel using ultrafast techniques up at extreme ultraviolet energies, which permit element-specific investigations. The element and time-resolved delay scans reveal a non-trivial interaction between spin excitations on the different magnetic sub-lattices of the magnetic insulator.
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| 17. |
- Lucchese, Robert, et al.
(författare)
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Vibrationally resolved partial cross sections and asymmetry parameters for nitrogen K-shell photoionization of the N2O molecule
- 2007
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 76:1, s. 012506-
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Tidskriftsartikel (refereegranskat)abstract
- We have measured the vibrationally resolved partial cross sections σ(v1′,v2′,v3′) and asymmetry parameters β(v1′,v2′,v3′) for Nc and Nt K-shell photoionization of the N2O molecule in the σ* shape resonance region above the Nt and Nc K-shell ionization thresholds. Nc K-shell photoionization of the N2O molecule predominantly causes the excitation of the quasisymmetric vibrations (v1′), whereas Nt K-shell photoionization causes both quasisymmetric and quasiantisymmetric vibrations (v1′ and v3′) to be excited. The shape resonance energy in the Nc K-shell photoionization increases with an increase in v1′. The β(v1′,0,0) curves for the Nc K-shell photoionization exhibit maxima at energies close to the shape resonance energies for the individual values of v1′. The shape resonance energy in the Nt K-shell photoionization decreases with an increase in v1′ and slightly increases with an increase in v3′. The β(v1′,0,0) curves show a significant state dependence in the region of the shape resonance, with the curves shifting to lower energy as v1′ increases. The vibrational state dependence of the cross sections σ(v1′,v2′,v3′) and asymmetry parameters β(v1′,v2′,v3′) are well reproduced by the theoretical calculations using the multichannel Schwinger configuration interaction (MCSCI) method, including both the Nc and Nt ion states.
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| 18. |
- Malik, Rameez Saeed, 1987-, et al.
(författare)
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Ultrafast dynamics in Fe65Co35 alloys: Effect of Re doping
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Annan publikation (populärvet., debatt m.m.)abstract
- Soft magnetic FeCo alloys are of great interest due to their potential spintronics applications. The magnetic damping parameter plays a vital role in the performance of these spintronics devices. The Gilbert damping parameter increase in these alloys with doping of 5d elements. Here, we have investigated the effect of Re doping on the element-specific magnetization dynamics of Ru/Fe65Co35/Ru thin films using the time-resolved magneto-optical Kerr effect. When varying the concentration of Re from 0 to 12.6 %, no change of the demagnetization time constant is observed. However, a gradual change of the remagnetization time is observed with the increase of Re concentration. This remagnetization dynamics can be related to the Gilbert damping parameter of these films. An interesting time-resolved dynamics at the Ru-edge is observed. A significant increase (40%) of the asymmetry signal is observed for the undoped sample and drops down with the Re doping. This effect is possibly a super diffusive spin current going from the magnetic layer to the non magnetic capping layer.
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| 19. |
- Malik, Rameez Saeed, 1987-, et al.
(författare)
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Ultrafast magnetization dynamics in half-metallic Co2FeAl Heusler alloy
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Annan publikation (populärvet., debatt m.m.)abstract
- We report on optically induced, ultrafast magnetization dynamics in the Heusler alloy Co2FeAl,probed by time-resolved magneto-optical Kerr effect. Experimental results are compared to resultsfrom electronic structure theory and atomistic spin-dynamics simulations. Experimentally, we findthat the demagnetization time (τM) in films of Co2FeAl is almost independent of varying structuralorder, and that it is similar to that in elemental 3d ferromagnets. In contrast, the slower processof magnetization recovery, specified byτR, is found to occur on picosecond time scales, and isdemonstrated to correlate strongly with the Gilbert damping parameter (α). Our results showthat Co2FeAl is unique, in that it is the first material that clearly demonstrates the importance ofthe damping parameter in the remagnetization process. Based on these results we argue that for Co2FeAl the remagnetization process is dominated by magnon dynamics, something which mighthave general applicabilit
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| 20. |
- Malik, Rameez Saeed, 1987-, et al.
(författare)
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Ultrafast magnetization dynamics in magnetically frustrated NiFe2O4 ferrimagnet
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Annan publikation (populärvet., debatt m.m.)abstract
- NiFe2O4 shows complex dynamics between its elements after an ultrashort laser pulse excitation. The reflectivity shows oscillations, indicating either a reordering of the charge distribution several picoseconds after absorption of the laser pulse or a coherent phonon mode with a frequency of 0.5 THz. Also, the magnetic asymmetry exhibits oscillations that cannot be attributed to transverse magnetic excitations (magnons) but correspond to longitudinal excitations. The demagnetization shows different behavior depending on the excitation photon energy, for energies close to the band gap (1.55 eV) oscillations in the asymmetry are prominent, while for higher energies (3.1 eV) the demagnetization becomes dominant and the oscillations vanish. A fast demagnetization is observed when using 3.1 eV compared to 1.55 eV, while the electronic response remains similar, which indicates that the fast demagnetization dynamics is driven by holes created deeper in the valence band while the dynamics of electrons excited to d-states in the conduction band provides a smaller contribution to the demagnetization.The oscillations in the asymmetry can be a consequence of the competing exchange interactions that are antiferromagnetic between all three sublattices, but where a ferromagnetic alignment between octahedral Ni and octahedral Fe is the ground state.
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| 21. |
- Malik, Rameez Saeed, 1987-, et al.
(författare)
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Ultrafast magnetization dynamics in the half-metallic Heusler alloy Co2FeAl
- 2021
-
Ingår i: Physical Review B. - : American Physical Society. - 2469-9950 .- 2469-9969. ; 104:10
-
Tidskriftsartikel (refereegranskat)abstract
- We report on optically induced, ultrafast magnetization dynamics in the Heusler alloy Co2FeAl, probed by time-resolved magneto-optical Kerr effect. Experimental results are compared to results from electronic structure theory and atomistic spin-dynamics simulations. Experimentally, we find that the demagnetization time (tau(M)) in films of Co2FeAl is almost independent of varying structural order, and that it is similar to that in elemental 3d ferromagnets. In contrast, the slower process of magnetization recovery, specified by tau(R), is found to occur on picosecond time scales, and is demonstrated to correlate strongly with the Gilbert damping parameter (alpha). Based on these results we argue that for Co2FeAl the remagnetization process is dominated by magnon dynamics, something which might have general applicability.
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| 22. |
- Ronchi, Emanuele, 1978-, et al.
(författare)
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A neural network pulse shape discrimination and pile-up rejection framework for the BC501 neutron/gamma liquid scintillator
- 2009
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Ingår i: Nuclear Instruments and Methods in Physics Research Section A. - : Elsevier BV. - 0168-9002 .- 1872-9576. ; 610:2, s. 534-539
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Tidskriftsartikel (refereegranskat)abstract
- BC-501 is a liquid scintillation detector sensitive to both neutrons and gamma rays. As these produce slightly different signals in the detector, they can be discriminated based on their pulse shape (Pulse Shape Discrimination, PSD). This paper reports on results obtained with several PSD techniques and compares them with a method based on artificial neural networks (NN) developed for this application. Results indicated a large performance advantage of NN especially in the region of small deposited energy which typically contains the majority of the events. NN were also applied for discrimination of pile-up events with good results. This framework can be implemented on some of the most recent programmable data acquisition cards and it is suitable for real-time application.
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| 23. |
- Stefanuik, Robert, et al.
(författare)
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Developments and enhancements to the HELIOS pump probe system
- 2018
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Ingår i: Journal of Electron Spectroscopy and Related Phenomena. - : Elsevier. - 0368-2048 .- 1873-2526. ; 224, s. 33-37
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Tidskriftsartikel (refereegranskat)abstract
- In this progress report we describe several design improvements that have been implemented at the HELIOS laboratory, as well as presenting the output characteristics that have been measured as a result. The main focus will be on the redesign of the gas cell, which has enhanced the photon flux of the XUV probe beam. Also, a frequency trippler utilizing sum frequency generation has been installed at the end of the pump line, which increases the photon flux available for both 3.1 eV (400 nm) and 4.66 eV (266 nm) applications without significant increment in the pulse width of the pump.
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| 24. |
- Ström, Magnus, et al.
(författare)
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Magnetic-field induced enhancement in the fluorescence yield spectrum of doubly excited states in helium
- 2006
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 97:25, s. 253002-
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Tidskriftsartikel (refereegranskat)abstract
- An influence of static magnetic fields on the fluorescence yield spectrum of He in the vicinity of the N=2 thresholds has been observed. The experimental results are in excellent agreement with predictions based on multichannel quantum defect theory, and it is demonstrated that the Rydberg electron ℓ mixing due to the diamagnetic interaction is essential for the description of the observed fluorescence yield intensity enhancement.
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| 25. |
- Söderström, Elisabet, et al.
(författare)
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Plasma cotinine is positively associated with homocysteine in smokers but not in users of smokeless tobacco
- 2021
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Ingår i: International Journal of Environmental Research and Public Health. - : MDPI. - 1661-7827 .- 1660-4601. ; 18:21
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Tidskriftsartikel (refereegranskat)abstract
- Plasma total homocysteine (tHcy) is a risk marker, and smoking is an established risk factor for cardiovascular disease. It is unclear if the effect of smoked tobacco on homocysteine is mediated by nicotine or other combustion products in smoked tobacco. Snus (moist smokeless tobacco) is high nicotine-containing tobacco, and little is known about the effect of snus on plasma homocysteine. Therefore, we studied, in a cross-section of subjects (n = 1375) from the Northern Sweden Health and Disease Study, with strictly defined current smokers (n = 194) and snus users (n = 47), the impact of tobacco exposure on tHcy, assessed by self-reported tobacco habits and plasma cotinine concentrations. The snus users had higher cotinine concentrations than the smokers. Cotinine, creatinine, methylmalonic acid, and the methylenetetrahydrofolate reductase genotype (MTHFR) T allele were positively associated with tHcy among the smokers, but not among the snus users. No association was observed between tHcy and the number of cigarettes/day. There was a positive association between cotinine and tHcy in the smokers, but not among the snus users. This indicates that substances other than nicotine in tobacco smoke could be responsible for the differential effects on homocysteine status. Self-reported smoking should be complemented by a cotinine assay whenever possible.
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