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Magnetic properties of Fe5SiB2 and its alloys with P, S, and Co
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Polish Acad Sci, Inst Mol Phys, Ul M Smoluchowskiego 17, PL-60179 Poznan, Poland..
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
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2016 (English)In: PHYSICAL REVIEW B, ISSN 2469-9950, Vol. 93, no 17, 174412Article in journal (Refereed) Published
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Text
Abstract [en]

Fe5SiB2 has been synthesized and magnetic measurements have been carried out, revealing that M-sat = 0.92 MA/mat T = 300 K. The M versus T curve shows a broad peak around T = 160 K. The anisotropy constant K-1, estimated at T = 300 K, is 0.25 MJ/m(3). Theoretical analysis of Fe5SiB2 system has been carried out and extended to the full range of Fe5Si1-xPxB2, Fe5P1-xSxB2, and (Fe1-xCox)(5)SiB2 compositions. The electronic band structures have been calculated using the full-potential local-orbital minimum-basis scheme (FPLO-14). The calculated total magnetic moments are 9.20, 9.15, 9.59, and 2.42 mu(B) per formula units of Fe5SiB2, Fe5PB2, Fe5SB2, and Co5SiB2, respectively. In agreement with experiment, magnetocrystalline anisotropy energies (MAE's) calculated for T = 0 K change from a negative (easy-plane) anisotropy -0.28 MJ/m(3) for Fe5SiB2 to the positive (easy-axis) anisotropy 0.35 MJ/m(3) for Fe5PB2. Further increase of the number of p electrons in Fe5P1-xSxB2 leads to an increase of MAE up to 0.77 MJ/m(3) for the hypothetical Fe5P0.4S0.6B2 composition. Volume variation and fixed spin moment calculations (FSM) performed for Fe5SiB2 show an inverse relation between MAE and magnetic moment in the region down to about 15% reduction of the spin moment. The alloying of Fe5SiB2 with Co is proposed as a practical realization of magnetic moment reduction, which ought to increase MAE. MAE calculated in virtual crystal approximation (VCA) for a full range of (Fe1-xCox)(5)SiB2 compositions reaches the maximum value of 1.16 MJ/m(3) at Co concentration x = 0.3, with the magnetic moment 7.75 mu(B) per formula unit. Thus, (Fe0.7Co0.3)(5)SiB2 is suggested as a candidate for a rare-earth free permanent magnet. For the stoichiometric Co5SiB2 there is an easy-plane magnetization, with the value of MAE = -0.15 MJ/m(3).

Place, publisher, year, edition, pages
2016. Vol. 93, no 17, 174412
National Category
Physical Sciences Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-298092DOI: 10.1103/PhysRevB.93.174412ISI: 000376244900004OAI: oai:DiVA.org:uu-298092DiVA: diva2:944514
Funder
Göran Gustafsson Foundation for Research in Natural Sciences and MedicineSwedish Research CouncilEU, FP7, Seventh Framework Programme
Available from: 2016-06-29 Created: 2016-06-29 Last updated: 2017-01-25Bibliographically 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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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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Kontos, SofiaGunnarsson, KlasSvedlindh, PeterCedervall, JohanSahlberg, MartinEdström, AlexanderEriksson, OlleRusz, Jan
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