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- Dussaux, A., et al.
(författare)
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Local dynamics of topological magnetic defects in the itinerant helimagnet FeGe.
- 2016
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Chiral magnetic interactions induce complex spin textures including helical and conical spin spirals, as well as particle-like objects such as magnetic skyrmions and merons. These spin textures are the basis for innovative device paradigms and give rise to exotic topological phenomena, thus being of interest for both applied and fundamental sciences. Present key questions address the dynamics of the spin system and emergent topological defects. Here we analyse the micromagnetic dynamics in the helimagnetic phase of FeGe. By combining magnetic force microscopy, single-spin magnetometry and Landau-Lifschitz-Gilbert simulations we show that the nanoscale dynamics are governed by the depinning and subsequent motion of magnetic edge dislocations. The motion of these topologically stable objects triggers perturbations that can propagate over mesoscopic length scales. The observation of stochastic instabilities in the micromagnetic structure provides insight to the spatio-temporal dynamics of itinerant helimagnets and topological defects, and discloses open challenges regarding their technological usage.
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- Koumpouras, Konstantinos, et al.
(författare)
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A majority gate with chiral magnetic solitons
- 2018
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 30:37
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Tidskriftsartikel (refereegranskat)abstract
- In magnetic materials, nontrivial spin textures may emerge due to the competition among different types of magnetic interactions. Among such spin textures, chiral magnetic solitons represent topologically protected spin configurations with particle-like properties. Based on atomistic spin dynamics simulations, we demonstrate that these chiral magnetic solitons are ideal to use for logical operations, and we demonstrate the functionality of a three- input majority gate, in which the input states can be controlled by applying an external electromagnetic field or spin-polarized currents. One of the main advantages of the proposed device is that the input and output signals are encoded in the chirality of solitons, that may be moved, allowing to perform logical operations using only minute electric currents. As an example we illustrate how the three input majority gate can be used to perform logical relations, such as Boolean AND and OR.
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- Koumpouras, Konstantinos, et al.
(författare)
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A spin dynamics approach to solitonics
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- In magnetic materials a variety of non-collinear ground state configurations may emerge as a result of competition among exchange, anisotropy, and dipole-dipole interaction, yielding magnetic states far more complex than those of homogenous ferromagnets. Of particular interest in this study are particle-like configurations. These particle-like states, e.g., magnetic solitons, skyrmions, or domain walls, form a spatially localised clot of magnetic energy. In this paper we address topologically protected magnetic solitons and explore concepts that potentially might be relevant for logical operations and/or information storage in the rapidly advancing filed of solitonics (and skyrmionics). An ability to easily create, address, and manipulate such structures is among the prerequisite forming a basis of "-onics technology", and is investigated in detail here using numerical and analytical tools.
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- Koumpouras, Konstantinos
(författare)
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Atomistic spin dynamics and relativistic effects in chiral nanomagnets
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this thesis, studies based on magnetization dynamics on atomic length scales are presented for a number of magnetic systems, where Dzyaloshinskii-Moriya (DM) interaction is present. First-principle methods, based on density functional theory (DFT), have been used to study the pairwise magnetic interactions, such as Heisenberg exchange and DM interaction, which are the crucial parameters for the helimagnetic systems. The first part of this thesis concerns the theoretical background: basics of DFT, atomistic spin dynamics and magnetic skyrmions. The second part concerns the ground state and dynamical properties of helimagnets.Magnetic interaction parameters have been calculated for heterostructures, such as Co/Ni/Co on heavy metal non-magnetic substrates. These parameters are strongly dependent on the material of the substrate. Furthermore, the magnetization dynamics of domain wall and skyrmion are studied and our results show that motion is influenced by the spin-Hall effect (SHE) which arises from the non-magnetic substrate. Similar studies of magnetic interaction parameters have been made for several half-Heusler compounds MnZSn (Z=Tc, Ru, Rh, Os, Ir and Pt) and the phase diagram of the MnPt0.99Ir0.01Sn alloy proves the existence of skyrmions in a wide range of temperature and external magnetic field. The manipulation of low-dimensional magnetic structures (skyrmions and solitons) with spin transfer torques have been investigated. The nucleation and annihilation processes of skyrmion, by the use of spin polarised current, are essential and the impact of different edges (antiferromagnetic, magnetically softer and stiffer) on both processes is studied. When the edge is magnetically softer, less current is required for skyrmion nucleation and annihilation. Furthermore, one-dimensional magnetic solitons are used to explore concepts of logical operations in a prototype majority gate device, since they are stable and can be easily created and manipulated by spin currents.Lastly, edge dislocations in FeGe helimagnet have been studied. These dislocations described in terms of thermally driven dynamics by the use of atomistic spin dynamics approach and possibly explain some unusual jumps of the spiral wavelength observed by time-dependent experiments.
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