| 1. |
- Boulle, Olivier, et al.
(författare)
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Non-adiabatic spin transfer torque in high anisotropic magnetic nanowires with narrow domain walls
- 2008
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 101:21, s. 1-4
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Tidskriftsartikel (refereegranskat)abstract
- Current induced domain wall (DW) depinning of a narrow DW in out-of-plane magnetized (Pt/Co)3/Pt multilayer elements is studied by magnetotransport. We find that for conventional measurements Joule heating effects conceal the real spin torque efficiency and so we use a measurement scheme at a constant sample temperature to unambiguously extract the spin torque contribution. From the variation of the depinning magnetic field with the current pulse amplitude we directly deduce the large nonadiabaticity factor in this material and we find that its amplitude is consistent with a momentum transfer mechanism.
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| 2. |
- Dohi, Takaaki, et al.
(författare)
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Enhanced thermally-activated skyrmion diffusion with tunable effective gyrotropic force
- 2023
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Magnetic skyrmions, topologically-stabilized spin textures that emerge in magnetic systems, have garnered considerable interest due to a variety of electromagnetic responses that are governed by the topology. The topology that creates a microscopic gyrotropic force also causes detrimental effects, such as the skyrmion Hall effect, which is a well-studied phenomenon highlighting the influence of topology on the deterministic dynamics and drift motion. Furthermore, the gyrotropic force is anticipated to have a substantial impact on stochastic diffusive motion; however, the predicted repercussions have yet to be demonstrated, even qualitatively. Here we demonstrate enhanced thermally-activated diffusive motion of skyrmions in a specifically designed synthetic antiferromagnet. Suppressing the effective gyrotropic force by tuning the angular momentum compensation leads to a more than 10 times enhanced diffusion coefficient compared to that of ferromagnetic skyrmions. Consequently, our findings not only demonstrate the gyro-force dependence of the diffusion coefficient but also enable ultimately energy-efficient unconventional stochastic computing.
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| 3. |
- Ge, Yuqing, 1996, et al.
(författare)
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Constructing coarse-grained skyrmion potentials from experimental data with Iterative Boltzmann Inversion
- 2023
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Ingår i: Communications Physics. - : Springer Science and Business Media LLC. - 2399-3650. ; 6:1
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Tidskriftsartikel (refereegranskat)abstract
- In an effort to understand skyrmion behavior on a coarse-grained level, skyrmions are often described as 2D quasiparticles evolving according to the Thiele equation. Interaction potentials are the key missing parameters for predictive modeling of experiments. Here, the Iterative Boltzmann Inversion technique commonly used in soft matter simulations is applied to construct potentials for skyrmion-skyrmion and skyrmion-magnetic material boundary interactions from a single experimental measurement without any prior assumptions of the potential form. It is found that the two interactions are purely repulsive and can be described by an exponential function for micrometer-sized skyrmions in a ferromagnetic thin film multilayer stack. This captures the physics on experimental length and time scales that are of interest for most skyrmion applications and typically inaccessible to atomistic or micromagnetic simulations.
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| 4. |
- Gupta, Rahul
(författare)
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Spin Current Generation in Magnetic Heterostructures and its Impact on Terahertz Emission : A Spin Dynamics Perspective
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The transfer of knowledge from one generation to another is key to the intellectualness of mankind. In the present information age, digital technology provides easy access to knowledge and information. However people across the globe simultaneously generate an enormous digital footprint, which demands to store and process the information in a modish way. Spin-based electronics is being considered a prospective candidate beyond complementary metal-oxide-semiconductor technology with several applications in data storage and data communication. The key concept of this technology is the generation, transportation, and detection of spin currents in magnetic heterostructures consisting of ferromagnetic (FM) and non-ferromagnetic (NFM) bilayer thin films.In this thesis, I describe the concepts of spin dynamics at the nano- to femtosecond timescales and experimental techniques used to extract the spin dynamics properties of magnetic heterostructures. In this regard, we have shown that the Gilbert damping parameter and the number of quantum conductance channels (QCCs) can be enhanced by doping the FM layer with Re in the Ru/Fe65Co35/Ru heterostructure. The same heterostructure was used to evidence superdiffusive spin transport and a proximity induced magnetic moment in the Ru layer. It has also been shown that the number of QCCs can be enhanced by inserting a Cu layer at the interface between the FM and NFM layers in the Co2FeAl/β-Ta heterostructure where the Gilbert damping parameter of Co2FeAl depends on its chemical ordering. Further, we have found that the spin torque (SOT) efficiency in the 2D-transition metal dichalcogenide, 1T-TaS2, based heterostructure is one order larger as compared to Co2FeAl/β-Ta and Fe/Pd heterostructures. Moreover, it has been shown that crystalline quality and strain engineering can significantly impact the SOT efficiency and emission of terahertz radiation in Fe/Pd and Fe/Pt heterostructures, respectively. Finally, a full Heusler (Co2FeAl) based spintronic terahertz emitter is presented, which utilizes an optically induced spin current and the inverse spin Hall effect phenomenon. This thesis provides useful insights in the pathway towards power efficient spin logic devices.
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| 5. |
- Zhou Hagström, Nanna, 1993-, et al.
(författare)
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Megahertz-rate Ultrafast X-ray Scattering and Holographic Imaging at the European XFEL
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence, and pulse duration. All XFEL facilities built until recently provided X-ray pulses at a relatively low repetition rate, with limited data statistics. Here, we present the results from the first megahertz repetition rate X-ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL. We illustrate the experimental capabilities that the SCS instrument offers, resulting from the operation at MHz repetition rates and the availability of the novel DSSC 2D imaging detector. Time-resolved magnetic X-ray scattering and holographic imaging experiments in solid state samples were chosen as representative examples, providing an ideal test-bed for operation at megahertz rates. Nevertheless, our results are relevant and applicable to any other non-destructive XFEL experiments in the soft X-ray range.
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| 6. |
- Zhou Hagström, Nanna, 1993-, et al.
(författare)
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Megahertz-rate ultrafast X-ray scattering and holographic imaging at the European XFEL
- 2022
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Ingår i: Journal of Synchrotron Radiation. - : International Union of Crystallography (IUCr). - 0909-0495 .- 1600-5775. ; 29, s. 1454-1464
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Tidskriftsartikel (refereegranskat)abstract
- The advent of X-ray free-electron lasers (XFELs) has revolutionized fundamental science, from atomic to condensed matter physics, from chemistry to biology, giving researchers access to X-rays with unprecedented brightness, coherence and pulse duration. All XFEL facilities built until recently provided X-ray pulses at a relatively low repetition rate, with limited data statistics. Here, results from the first megahertz-repetition-rate X-ray scattering experiments at the Spectroscopy and Coherent Scattering (SCS) instrument of the European XFEL are presented. The experimental capabilities that the SCS instrument offers, resulting from the operation at megahertz repetition rates and the availability of the novel DSSC 2D imaging detector, are illustrated. Time-resolved magnetic X-ray scattering and holographic imaging experiments in solid state samples were chosen as representative, providing an ideal test-bed for operation at megahertz rates. Our results are relevant and applicable to any other non-destructive XFEL experiments in the soft X-ray range.
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