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From soft to hard magnetic Fe-Co-B by spontaneous strain: a combined first principles and thin film study
IFW Dresden, D-01171 Dresden, Germany.;Tech Univ Dresden, Inst Mat Sci, Fac Mech Engn, D-01062 Dresden, Germany..
IFW Dresden, D-01171 Dresden, Germany.;Tech Univ Dresden, Inst Mat Sci, Fac Mech Engn, D-01062 Dresden, Germany..
IFW Dresden, D-01171 Dresden, Germany..
IFW Dresden, D-01171 Dresden, Germany..
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2015 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 27, no 47, 476002Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

In order to convert the well-known Fe-Co-B alloy from a soft to a hard magnet, we propose tetragonal strain by interstitial boron. Density functional theory reveals that when B atoms occupy octahedral interstitial sites, the bcc Fe-Co lattice is strained spontaneously. Such highly distorted Fe-Co is predicted to reach a strong magnetocrystalline anisotropy which may compete with shape anisotropy. To probe this theoretical suggestion experimentally, epitaxial films are examined. A spontaneous strain up to 5% lattice distortion is obtained for B content up to 4 at%, which leads to uniaxial anisotropy constants exceeding 0.5 MJ m(-3). However, a further addition of B results in a partial amorphisation, which degrades both anisotropy and magnetisation.

Place, publisher, year, edition, pages
2015. Vol. 27, no 47, 476002
Keyword [en]
Fe-Co, rare-earth free permanent magnet, magnetocrystalline anisotropy, tetragonal strain, DFT
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-270417DOI: 10.1088/0953-8984/27/47/476002ISI: 000365346800013PubMedID: 26548574OAI: oai:DiVA.org:uu-270417DiVA: diva2:895727
Funder
Swedish National Infrastructure for Computing (SNIC), SNIC 001/12-198
Available from: 2016-01-19 Created: 2015-12-28 Last updated: 2017-11-30
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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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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Edstrom, AlexanderDelczeg-Czirjak, Erna K.Rusz, Jan

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