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Enhanced spin–orbit coupling in tetragonally strained Fe–Co–B films
University of Duisburg-Essen, Germany.
IFW Dresden, Germany.
University of Duisburg-Essen, Germany.
Ruhr-Universität Bochum, Germany.
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2017 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 9, no 27, 275802Article in journal (Refereed) Published
Abstract [en]

Tetragonally strained interstitial Fe-Co-B alloys were synthesized as epitaxial films grown on a 20 nm thick Au0.55Cu0.45 buffer layer. Different ratios of the perpendicular to in-plane lattice constant c/a = 1.013, 1.034 and 1.02 were stabilized by adding interstitial boron with different concentrations 0, 4, and 10 at.%, respectively. Using ferromagnetic resonance (FMR) and x-ray magnetic circular dichroism (XMCD) we found that the total orbital magnetic moment significantly increases with increasing c/a ratio, indicating that reduced crystal symmetry and interstitial B leads to a noticeable enhancement of the effect of spin-orbit coupling (SOC) in the Fe-Co-B alloys. First-principles calculations reveal that the increase in orbital magnetic moment mainly originates from B impurities in octahedral position and the reduced symmetry around B atoms. These findings offer the possibility to enhance SOC phenomena-namely the magnetocrystalline anisotropy and the orbital moment-by stabilizing anisotropic strain by doping 4 at.% B. Results on the influence of B doping on the Fe-Co film microstructure, their coercive field and magnetic relaxation are also presented.

Place, publisher, year, edition, pages
2017. Vol. 9, no 27, 275802
Keyword [en]
magnetism, spin-orbit, magnetic anisotropy, FRM, XMCD, DFT
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-304518DOI: 10.1088/1361-648X/aa7498ISI: 000403326600001PubMedID: 28530633OAI: oai:DiVA.org:uu-304518DiVA: diva2:1033178
Funder
EU, FP7, Seventh Framework Programme, 280670Swedish Research Council
Note

Title in list of papers in Thesis: Enhanced and Tunable Spin-Orbit Coupling in tetragonally Strained Fe-Co-B Films

Available from: 2016-10-06 Created: 2016-10-06 Last updated: 2017-08-22Bibliographically approved
In thesis
1. Theoretical and Computational Studies on the Physics of Applied Magnetism: Magnetocrystalline Anisotropy of Transition Metal Magnets and Magnetic Effects in Elastic Electron Scattering
Open this publication in new window or tab >>Theoretical and Computational Studies on the Physics of Applied Magnetism: Magnetocrystalline Anisotropy of Transition Metal Magnets and Magnetic Effects in Elastic Electron Scattering
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, two selected topics in magnetism are studied using theoretical modelling and computational methods. The first of these is the magnetocrystalline anisotropy energy (MAE) of transition metal based magnets. In particular, ways of finding 3d transition metal based materials with large MAE are considered. This is motivated by the need for new permanent magnet materials, not containing rare-earth elements, but is also of interest for other technological applications, where the MAE is a key quantity. The mechanisms of the MAE in the relevant materials are reviewed and approaches to increasing this quantity are discussed. Computational methods, largely based on density functional theory (DFT), are applied to guide the search for relevant materials. The computational work suggests that the MAE of Fe1-xCox alloys can be significantly enhanced by introducing a tetragonality with interstitial B or C impurities. This is also experimentally corroborated. Alloying is considered as a method of tuning the electronic structure around the Fermi energy and thus also the MAE, for example in the tetragonal compound (Fe1-xCox)2B. Additionally, it is shown that small amounts (2.5-5 at.%) of various 5d dopants on the Fe/Co-site can enhance the MAE of this material with as much as 70%. The magnetic properties of several technologically interesting, chemically ordered, L10 structured binary compounds, tetragonal Fe5Si1-xPxB2 and Hexagonal Laves phase Fe2Ta1-xWx are also investigated. The second topic studied is that of magnetic effects on the elastic scattering of fast electrons, in the context of transmission electron microscopy (TEM). A multislice solution is implemented for a paraxial version of the Pauli equation. Simulations require the magnetic fields in the sample as input. A realistic description of magnetism in a solid, for this purpose, is derived in a scheme starting from a DFT calculation of the spin density or density matrix. Calculations are performed for electron vortex beams passing through magnetic solids and a magnetic signal, defined as a difference in intensity for opposite orbital angular momentum beams, integrated over a disk in the diffraction plane, is observed. For nanometer sized electron vortex beams carrying orbital angular momentum of a few tens of ħ, a relative magnetic signal of order 10-3 is found. This is considered realistic to be observed in experiments. In addition to electron vortex beams, spin polarised and phase aberrated electron beams are considered and also for these a magnetic signal, albeit weaker than that of the vortex beams, can be obtained.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 109 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1440
Keyword
Magnetism, Magnetic anisotropy, DFT, Permanent magnets, Electron vortex beams, Electron microscopy, Electron scattering, Multislice methods, Magnetism, magnetisk anisotropi, permanentmagneter, täthetsfunktionalteori, elektronmikroskopi, elektronvirvelstrålar, elektronspridningsteori
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-304666 (URN)978-91-554-9753-8 (ISBN)
Public defence
2016-11-25, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
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Supervisors
Note

Felaktigt ISBN i den tryckta versionen: 9789155497149

Available from: 2016-11-02 Created: 2016-10-07 Last updated: 2016-12-19Bibliographically approved

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Edström, AlexanderThonig, DannyRusz, JanEriksson, Olle

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