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Tuning skyrmions in B20 compounds by 4d and 5d doping
Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova. KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, SeRC - Swedish e-Science Research Centre.
Uppsala Univ, Dept Phys & Astron, Box 516, SE-75120 Uppsala, Sweden..
Uppsala Univ, Dept Chem, Box 538, SE-75121 Uppsala, Sweden..ORCID iD: 0000-0002-0096-4366
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2022 (English)In: Physical Review Materials, E-ISSN 2475-9953, Vol. 6, no 8, article id 084401Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
American Physical Society (APS) , 2022. Vol. 6, no 8, article id 084401
National Category
Nano Technology Condensed Matter Physics Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-316724DOI: 10.1103/PhysRevMaterials.6.084401ISI: 000838143600001Scopus ID: 2-s2.0-85137268142OAI: oai:DiVA.org:kth-316724DiVA, id: diva2:1691482
Note

QC 20220830

Available from: 2022-08-30 Created: 2022-08-30 Last updated: 2024-05-07Bibliographically approved
In thesis
1. Computational and Algorithmic Approaches for Studying Exotic Spin Textures
Open this publication in new window or tab >>Computational and Algorithmic Approaches for Studying Exotic Spin Textures
2024 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Exotic spin textures such as skyrmions, are proved to be promising candidates for the development of sustainable, next-generation spintronic devices. Despite extensive research in this domain, the quest for efficient computational methodologies for the automated discovery of novel functional magnetic materials, and identify the intricate topological spin textures they can host, remains a formidable challenge in solid-state physics. This thesis work introduces a promising end-to-end computational approach, employing the Heisenberg spin Hamiltonian model, aimed at overcoming this challenge and discovering novel exotic spin textures. Our approaches encompass an automated Density Functional Theory (DFT) calculation workflow designed to predict candidate functional magnetic materials for hosting spin textures, with those candidate material we calculate their magnetic exchange interactions for constructing the spin Hamiltonian. Subsequently, a computational workflow that integrates new developed metaheuristic optimization algorithms with Atomistic Spin Dynamics (ASD) simulations is employed to identify spin textures in targeted systems. Additionally, a post-processing tool for the visualization of these textures is presented.

In the computational approach part of this work, we have developed several tools, including the high-throughput workflow code and the scientific visualization software, dedicated to studying exotic spin textures. On the algorithmic front, we introduce the metaheuristic conditional neural network and a controlled assembly approach for investigating the long-lifetime metastable states of magnetic systems with long-range interactions. Through these novel approaches, we have identified and predicted the constructing pathways to several novel high-order antiskyrmions and three types of skyrmionic metamaterials (i.e., lattice-like, flake-like, and cell-like). Furthermore, we applied evolutionary algorithms for identifying the ground states of skyrmionic systems, developing both the genetic tunneling optimizer (GTO) and a neuroevolutionary algorithm.

In summary, the main results are:

1. Discovery and analysis of the forming mechanism of novel high-order antiskyrmions in the PdFeIr system.

2. Introduction of the evolutionary algorithm to the atomistic spin Hamiltonian model for the first time, combined with Markov chain Monte Carlo and atomistic spin dynamics simulations.

3. Prediction of skyrmions in 4d and 5d doped B20 systems.

4. Discovery and revealing the construction pathway of new skyrmionic textures, i.e., 2D skyrmionic metamaterials.

5. Development of a general visualization and post-processing code for computational magnetism, which offers new opportunities for analyzing complex spin textures.

Abstract [sv]

Exotiska spinntexturer såsom skyrmioner, är lovande kandidater för utvecklingen av nästa generations, hållbara spinntronik-enheter. Trots omfattande forskning inom detta område är sökandet efter effektiva beräkningsmetoder för den automatiserade upptäckten av nya funktionella magnetiska material och identifiering av de komplexa topologiska spintexturer de kan hysa, fortfarande en formidabel utmaning inom fasta tillståndets fysik. Detta avhandlingsarbete introducerar en lovande helhetslösning för beräkning, som använder Heisenberg spinn Hamiltonian-modellen, inriktad på att öve-rvinna denna utmaning och upptäcka nya exotiska spintexturer. Våra meto- der omfattar ett automatiserat arbetsflöde för beräkningar med täthetsfunkt- ionalteori (DFT)  som är utformat för att förutsäga kandidatmaterial för funktionella magnetiska material som kan hysa spinntexturer, med dessa kandidatmaterial beräknar vi deras magnetiska utbytesväxelverkan för att konstruera spinn-Hamiltonoperatorer. Därefter används ett beräkningsarbet- sflöde som integrerar nyligen utvecklade metaheuristiska optimeringsalgoritmer med atomistisk spinndynamik (ASD) simuleringar för att identifiera spinntexturer i riktade system. Vidare presenteras ett efterbehandlingsverktyg för visualisering av dessa texturer.

I den beräkningsmässiga delen av detta arbete har vi utvecklat flera verktyg, inklusive programvara för arbetsflöden med hög genomströmning, samt för vetenskaplig visualisering, tillägnad studier exotiska spintexturer. På den algoritmiska sidan introducerar vi det metaheuristiska villkorade neuronnätverket och en metod för kontrollerad sammansättning för att undersöka de långlivade metastabila tillstånden hos magnetiska system med växelverkan av lång räckvidd. Genom dessa nya metoder har vi identifierat konstruktionsvägar till flera nya högre ordningens antiskyrmioner och tre typer av skyrmioniska metamaterial (dvs. gitterliknande, flagliknande och celliknande). Dessutom var vi i tillämpningen av evolutionära algoritmer för att identifiera grundtillstånden hos skyrmioniska system, och utvecklade både den genetiska tunneloptimeraren (GTO) och en neuroevolutionär algoritm.

Sammanfattning av de huvudsakliga resultaten:

1. Upptäckt och analys av bildningsmekanismen för nya högordnings antiskyrmioner i PdFeIr-systemet.

2. Förutsägelse av skyrmioner i 4d- och 5d-dopade B20-system.

3. Första introduktionen av evolutionära algoritmer till atomistiska spinn-Hamiltonoperator, kombinerat med Markovkedje Monte Carlo och atomistiska spinndynamiksimuleringar.

4. Upptäckt av konstruktionsvägen för nya skyrmioniska texturer, exempelvis 2D skyrmioniska metamaterial.

5. Utveckling av en allmän visualiserings- och efterbehandlingskod för beräkningsmagnetism, vilket erbjuder nya möjligheter för analys av komplexa spinntexturer.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2024
Series
TRITA-SCI-FOU ; 2024:26
National Category
Natural Sciences Physical Sciences Condensed Matter Physics
Research subject
Physics, Material and Nano Physics; SRA - E-Science (SeRC); Physics, Theoretical Physics
Identifiers
urn:nbn:se:kth:diva-346223 (URN)978-91-8040-946-9 (ISBN)
Public defence
2024-05-24, 4204, Albanovägen 29, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 2024-05-07

Available from: 2024-05-07 Created: 2024-05-07 Last updated: 2024-05-20Bibliographically approved

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Xu, QichenWikfeldt, Kjartan ThorDelin, Anna

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Xu, QichenClulow, RebeccaShtender, VitaliiWikfeldt, Kjartan ThorDelin, Anna
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