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Microscopic Origin of Heisenberg and Non-Heisenberg Exchange Interactions in Ferromagnetic bcc Fe
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Fed Univ Para, Fac Fis, BR-66075110 Belem, Para, Brazil..
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
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2016 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 116, no 21, article id 217202Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

By means of first principles calculations, we investigate the nature of exchange coupling in ferromagnetic bcc Fe on a microscopic level. Analyzing the basic electronic structure reveals a drastic difference between the 3d orbitals of E-g and T-2g symmetries. The latter ones define the shape of the Fermi surface, while the former ones form weakly interacting impurity levels. We demonstrate that, as a result of this, in Fe the T-2g orbitals participate in exchange interactions, which are only weakly dependent on the configuration of the spin moments and thus can be classified as Heisenberg-like. These couplings are shown to be driven by Fermi surface nesting. In contrast, for the E-g states, the Heisenberg picture breaks down since the corresponding contribution to the exchange interactions is shown to strongly depend on the reference state they are extracted from. Our analysis of the nearest-neighbor coupling indicates that the interactions among E-g states are mainly proportional to the corresponding hopping integral and thus can be attributed to be of double-exchange origin. By making a comparison to other magnetic transition metals, we put the results of bcc Fe into context and argue that iron has a unique behavior when it comes to magnetic exchange interactions.

Place, publisher, year, edition, pages
2016. Vol. 116, no 21, article id 217202
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:uu:diva-298894DOI: 10.1103/PhysRevLett.116.217202ISI: 000376628800010PubMedID: 27284671OAI: oai:DiVA.org:uu-298894DiVA, id: diva2:948563
Funder
EU, European Research Council, 338957 FEMTO/NANOSwedish Research CouncileSSENCE - An eScience CollaborationKnut and Alice Wallenberg Foundation, 2012.0031 2013.0020
Available from: 2016-07-12 Created: 2016-07-12 Last updated: 2018-04-07Bibliographically approved
In thesis
1. Electronic structure and exchange interactions from ab initio theory: New perspectives and implementations
Open this publication in new window or tab >>Electronic structure and exchange interactions from ab initio theory: New perspectives and implementations
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, the magnetic properties of several materials were investigated using first principle calculations. The ab initio method named real space linear muffin-tin orbitals atomic sphere approximation (RS-LMTO-ASA) was used to calculate the electronic structure and magnetic properties of bulk systems, surface and nanostructures adsorbed on surfaces.

We have implemented new features in the RS-LMTO-ASA method, such as the calculation of (a) Bloch Spectral Function (BSF), (b) orbital resolved Jij and (c) Dzyaloshinskii-Moriya interaction (DMI). Using (a), we have shown that one can calculate the dispersion relation for bulk systems using a real space method. Furthermore, the dispersion relation was revealed to be existent even for finite one-dimensional structures, such as the Mn chain on Au(111) and Ag(111) surfaces. With (b), we have investigated the orbital resolved exchange coupling parameter Jij for 3d metals. It is demonstrated that the nearest neighbor (NN) interaction for bcc Fe has intriguing behavior, however, the contribution coming from the T2g orbitals favours the anti-ferromagnetic coupling behavior. Moreover, the Fermi surface for bcc Fe is formed mostly by the T2g orbitals and these are shown to be highly Heisenberg-like, i.e. do not depend significantly on the magnetic configuration. Later, the same approach was used to study other transition metals, such as Cr, Mn, Co and Ni. In the end, we have presented the results obtained with the implementation (c). Our results have shown the large dependence of the DMI values, both the strength and direction, with respect to which magnetic configuration they are calculated from. We argue that, for the investigated systems, the non-collinearity induces currents (spin and charge) that will influence directly the DMI vectors.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 85
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1663
Keyword
ab initio, exchange interactions, non-collinear magnetism
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-347812 (URN)978-91-513-0315-4 (ISBN)
Public defence
2018-05-29, Seminar Room, Universidade Federal do Pará, Av. Augusto Correa 01, Belém, PA, Brazil, Belém, 10:00 (English)
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The public defence can also be followed on livestream at Rosetta room, Ång/10239, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala

Available from: 2018-05-07 Created: 2018-04-07 Last updated: 2018-05-07

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Kvashnin, Yaroslav O.Szilva, AttilaDi Marco, IgorNordström, LarsEriksson, Olle

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