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Standard model of the rare earths analyzed from the Hubbard I approximation
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory. Radboud Univ Nijmegen, Inst Mol & Mat, Heyendaalseweg 135, NL-6525 AJ Nijmegen, Netherlands..
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. Fed Univ Para, Fac Fis, Belem, Para, Brazil..
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 B, ISSN 2469-9950, Vol. 94, no 8, 085137Article in journal (Refereed) Published
Abstract [en]

In this work we examine critically the electronic structure of the rare-earth elements by use of the so-called Hubbard I approximation. From the theoretical side all measured features of both occupied and unoccupied states are reproduced, without significant deviations between observations and theory. We also examine cohesive properties like the equilibrium volume and bulk modulus, where we find, in general, a good agreement between theory andmeasurements. In addition, we have reproduced the spin and orbital moments of these elements as they are reflected from measurements of the saturation moment. We have also employed the Hubbard I approximation to extract the interatomic exchange parameters of an effective spin Hamiltonian for the heavy rare earths. We show that the Hubbard I approximation gives results which are consistent with calculations where 4f electrons are treated as core states for Gd. The latter approach was also used to address the series of the heavy/late rare earths. Via Monte Carlo simulations we obtained ordering temperatures which reproduce measurements within about 20%. We have further illustrated the accuracy of these exchange parameters by comparing measured and calculated magnetic configurations for the heavy rare earths and the magnon dispersion for Gd. The Hubbard I approximation is compared to other theories of the electronic structure, and we argue that it is superior. We discuss the relevance of our results in general and how this makes it possible to treat the electronic structure of materials containing rare-earth elements, such as permanent magnets, magnetostrictive compounds, photovoltaics, optical fibers, topological insulators, and molecular magnets.

Place, publisher, year, edition, pages
2016. Vol. 94, no 8, 085137
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-303271DOI: 10.1103/PhysRevB.94.085137ISI: 000381889700004OAI: oai:DiVA.org:uu-303271DiVA: diva2:971450
Funder
eSSENCE - An eScience CollaborationSwedish Research CouncilKnut and Alice Wallenberg Foundation, 2013.0020 2012.0031EU, European Research Council, 338957 FEMTO/NANOThe Royal Swedish Academy of SciencesCarl Tryggers foundation Swedish Energy AgencySwedish Foundation for Strategic Research
Available from: 2016-09-16 Created: 2016-09-15 Last updated: 2016-11-29Bibliographically approved
In thesis
1. Theoretical methods for the electronic structure and magnetism of strongly correlated materials
Open this publication in new window or tab >>Theoretical methods for the electronic structure and magnetism of strongly correlated materials
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this work we study the interesting physics of the rare earths, and the microscopic state after ultrafast magnetization dynamics in iron. Moreover, this work covers the development, examination and application of several methods used in solid state physics. The first and the last part are related to strongly correlated electrons. The second part is related to the field of ultrafast magnetization dynamics.

In the first part we apply density functional theory plus dynamical mean field theory within the Hubbard I approximation to describe the interesting physics of the rare-earth metals. These elements are characterized by the localized nature of the 4f electrons and the itinerant character of the other valence electrons. We calculate a wide range of properties of the rare-earth metals and find a good correspondence with experimental data. We argue that this theory can be the basis of future investigations addressing rare-earth based materials in general.

In the second part of this thesis we develop a model, based on statistical arguments, to predict the microscopic state after ultrafast magnetization dynamics in iron. We predict that the microscopic state after ultrafast demagnetization is qualitatively different from the state after ultrafast increase of magnetization. This prediction is supported by previously published spectra obtained in magneto-optical experiments. Our model makes it possible to compare the measured data to results that are calculated from microscopic properties. We also investigate the relation between the magnetic asymmetry and the magnetization.

In the last part of this work we examine several methods of analytic continuation that are used in many-body physics to obtain physical quantities on real energies from either imaginary time or Matsubara frequency data. In particular, we improve the Padé approximant method of analytic continuation. We compare the reliability and performance of this and other methods for both one and two-particle Green's functions. We also investigate the advantages of implementing a method of analytic continuation based on stochastic sampling on a graphics processing unit (GPU).

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 109 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1461
Keyword
dynamical mean field theory (DMFT), Hubbard I approximation, strongly correlated systems, rare earths, lanthanides, photoemission spectra, ultrafast magnetization dynamics, analytic continuation, Padé approximant method, two-particle Green's functions, linear muffin tin orbitals (LMTO), density functional theory (DFT), cerium, stacking fault energy.
National Category
Natural Sciences Physical Sciences
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-308699 (URN)978-91-554-9770-5 (ISBN)
Public defence
2017-02-03, Ång/10132, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2017-01-12 Created: 2016-11-29 Last updated: 2017-01-17

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Locht, Inka L. M.Kvashnin, Yaroslav O.Rodrigues, Debora C. M.Pereiro, ManuelBergman, AndersDelin, AnnaJohansson, BörjeDi Marco, IgorEriksson, Olle
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