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Atomistic spin dynamics and relativistic effects in chiral nanomagnets
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Description
Abstract [en]

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.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2017. , p. 97
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1467
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-312462ISBN: 978-91-554-9791-0 (print)OAI: oai:DiVA.org:uu-312462DiVA, id: diva2:1063351
Public defence
2017-02-27, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2017-02-07 Created: 2017-01-10 Last updated: 2017-02-07
List of papers
1. A spin dynamics approach to solitonics
Open this publication in new window or tab >>A spin dynamics approach to solitonics
2016 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6, article id 25685Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-297269 (URN)10.1038/srep25685 (DOI)000375436700001 ()27156906 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation, KAW 2013.0020, KAW 2012.0031eSSENCE - An eScience CollaborationSwedish Research Council
Available from: 2016-06-23 Created: 2016-06-22 Last updated: 2017-11-28Bibliographically approved
2. Local dynamics of topological magnetic defects in the itinerant helimagnet FeGe.
Open this publication in new window or tab >>Local dynamics of topological magnetic defects in the itinerant helimagnet FeGe.
Show others...
2016 (English)In: Nature Communications, ISSN 2041-1723, E-ISSN 2041-1723, Vol. 7, article id 12430Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-291374 (URN)10.1038/ncomms12430 (DOI)000381773100001 ()27535899 (PubMedID)
Funder
Swedish Research CouncileSSENCE - An eScience Collaboration
Available from: 2016-05-02 Created: 2016-05-02 Last updated: 2017-11-30Bibliographically approved
3. A majority gate with chiral magnetic soliton
Open this publication in new window or tab >>A majority gate with chiral magnetic soliton
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-312433 (URN)
Available from: 2017-01-10 Created: 2017-01-09 Last updated: 2017-01-10
4. Relativistic interactions in low-dimensional Co heterostructure
Open this publication in new window or tab >>Relativistic interactions in low-dimensional Co heterostructure
(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-312434 (URN)
Available from: 2017-01-10 Created: 2017-01-09 Last updated: 2017-01-10
5. Search for high-temperature skyrmionic phase in Mn-based half-Heusler alloys from simulations
Open this publication in new window or tab >>Search for high-temperature skyrmionic phase in Mn-based half-Heusler alloys from simulations
(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-312460 (URN)
Available from: 2017-01-10 Created: 2017-01-10 Last updated: 2017-01-10
6. Relativistic effects in domain wall and skyrmion dynamics in magnetic heterostructures
Open this publication in new window or tab >>Relativistic effects in domain wall and skyrmion dynamics in magnetic heterostructures
(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-312435 (URN)
Available from: 2017-01-10 Created: 2017-01-09 Last updated: 2017-01-10
7. The effect of edge interactions on current driven creation and annihilation of skyrmions
Open this publication in new window or tab >>The effect of edge interactions on current driven creation and annihilation of skyrmions
(English)Manuscript (preprint) (Other academic)
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-312461 (URN)
Available from: 2017-01-10 Created: 2017-01-10 Last updated: 2017-01-18

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