Microscopic Origin of Heisenberg and Non-Heisenberg Exchange Interactions in Ferromagnetic bcc Fe

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.

Cardias, R.Fed Univ Para, Fac Fis, BR-66075110 Belem, Para, Brazil. (author)
Szilva, AttilaUppsala universitet,Materialteori(Swepub:uu)attsz286 (author)
Di Marco, IgorUppsala universitet,Materialteori(Swepub:uu)igodi229 (author)
Katsnelson, M. I.Radboud Univ Nijmegen, Inst Mol & Mat, Heijendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands.;Ural Fed Univ, Theoret Phys & Appl Math Dept, Mira St 19, Ekaterinburg 620002, Russia. (author)
Lichtenstein, A. I.Ural Fed Univ, Theoret Phys & Appl Math Dept, Mira St 19, Ekaterinburg 620002, Russia.;Univ Hamburg, Inst Theoret Phys, Jungiusstr 9, D-20355 Hamburg, Germany. (author)
Nordström, LarsUppsala universitet,Materialteori(Swepub:uu)larsnord (author)
Klautau, A. B.Fed Univ Para, Fac Fis, BR-66075110 Belem, Para, Brazil. (author)
Eriksson, OlleUppsala universitet,Materialteori(Swepub:uu)olleerik (author)
Uppsala universitetMaterialteori (creator_code:org_t)

By the author/editor: Kvashnin, Yarosl ...; Cardias, R.; Szilva, Attila; Di Marco, Igor; Katsnelson, M. I ...; Lichtenstein, A. ...; show more...; Nordström, Lars; Klautau, A. B.; Eriksson, Olle; show less...

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NATURAL SCIENCES: NATURAL SCIENCES; and Physical Science ...; and Other Physics To ...

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