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Theoretical studies of the incommensurate magnetic structure of a heavy fermion system: CeRhIn5
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science.
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 9, 094433- p.Article in journal (Refereed) Published
Abstract [en]

We have investigated the electronic structure and the incommensurate magnetic configuration of the pressure-induced superconductor CeRhIn5. Noncollinear first-principles calculations were performed in the local-density approximation plus U scheme. The observed magnetic configuration is described accurately in our calculations, especially considering the minute energy scale which is relevant (microelectron volt). The band structure and Fermi surfaces were investigated and nesting was found to be responsible for the complex noncollinear magnetic state of CeRhIn5.

Place, publisher, year, edition, pages
2010. Vol. 81, no 9, 094433- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-109676DOI: 10.1103/PhysRevB.81.094433ISI: 000276207300083OAI: oai:DiVA.org:uu-109676DiVA: diva2:273445
Available from: 2009-10-21 Created: 2009-10-21 Last updated: 2012-03-26Bibliographically approved
In thesis
1. Magnetic and Structural Properties of f-electron Systems from First Principles Theory
Open this publication in new window or tab >>Magnetic and Structural Properties of f-electron Systems from First Principles Theory
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A series of studies of f-electron systems based on density functional theory methods have been performed.  The focus of the studies has been on magnetic and structural properties, as well as investigating ways to handle strong electron correlation in these systems.

A version of the self-interaction correction (SIC) method has been developed for a full-potential linear muffin-tin orbital method. The method is demonstrated to have the strong capabilities of previous SIC implementations, to study energetics and phase stabilities of d- and f-electron systems with localisation-delocalisation transitions, but with no geometrical constraints from the underlying band structure method. The method is applied to the high-TC superconductor CeOFeAs, in which the f-shell of the Ce atoms is argued to undergo a Mott transition to a delocalised state under pressure.

The non-collinear magnetic structures of two rare earth compounds, TbNi5 and CeRhIn5 have been studied, and in both cases the complex magnetic ordering can be attributed to the effects of Fermi surface nesting.

The magnetic properties of the FeMnP0.75Si0.25 system has been studied and found to have an extreme sensitivity to the amount of disorder of the Fe-Mn sublattice.

Elements with valence f electrons typically exhibit very complex phase diagrams, with the frequently occurring phenomenon that they melt from a bcc phase that is unstable in calculations based solely on the electronic structure. The high temperature bcc phase of the elements La and Th were studied by means of the self-consistent ab initio lattice dynamics method that accounts for phonon-phonon interaction.

Delicate magnetic and structural properties are often sensible to details of how the Brillouin zone (BZ) integration is performed. An improved scheme is proposed that adapts to the BZ mesh and allows for better energy convergence of small energy differences in the smearing type methods.

Correlation effects in the 5f-states of plutonium has in recent years been the focus of attention for many theoretical studies employing extensions to DFT schemes. These different schemes have often produced large variations in 5f occupation numbers, and therefore a survey was made of experimental occupation numbers and 4f core level shifts to establish a value for the 5f occupation without any computational bias.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 82 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 686
National Category
Physical Sciences
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-109639 (URN)978-91-554-7644-1 (ISBN)
Public defence
2009-12-04, A80101, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2009-11-13 Created: 2009-10-21 Last updated: 2011-01-11Bibliographically approved
2. Non-collinear Magnetism in d- and f-electron Systems
Open this publication in new window or tab >>Non-collinear Magnetism in d- and f-electron Systems
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, non-collinear magnetism has been studied by using density functional theory and the augmented plane wave method with local orbitals (APW+lo). Two conditions for non-collinear instabilities have been identified in this thesis. First, the Fermi energy should cut through both spin up and down states. Secondly, strong nesting between the spin up and spin down Fermi surfaces is needed. The two criteria described here can be fulfilled by tuning the exchange-splitting and/or by modifying the volume. Calculations on several elements; bcc V, bcc and fcc Mn, bcc Fe, bcc and fcc Co, and bcc and fcc Ni show that a non-collinear state can be stabilized provided that the criteria discussed above are met. More complex materials have also been analyzed in terms of these two criteria. The substitutional alloys TlCo2Se2-xSx are found in experiments to possess spin spiral structures for x = {0-1.5} and at a concentration x = 1.75 the alloys become ferromagnetic. As S takes the place of Se in the crystal structure the distance between the Co layers is reduced and the turn angle of the spin spiral becomes smaller until it totally vanishes at x = 1.75. This thesis show that the evolution of the magnetic structure in these alloys is the consequence of a modification of the distance between Co layers, which induces a change in the interlayer exchange coupling.

Fermi surfaces have been analyzed in TbNi5 in order to determine nesting features which would be responsible for the magnetic spin spiral observed in this material. The electronic structure of CeRhIn5 is also reported in this thesis. Furthermore, the 3-k magnetic structure of UO2 was investigated and the crystal field levels were calculated. Transition metal systems such as Fe in the superconducting high-pressure hcp phase and in the fcc crystal structure were also studied. The results obtained for fcc Fe are in accordance with previous reports. However the paramagnetic state in hcp Fe is found to be more stable than the antiferromagnetic configurations discussed earlier in the literature as being favored in the volume range where the hcp phase is stable and superconductivity appears (~ 15 GPa). The complex non-collinear magnetic structure in Mn3IrSi was calculated and the results are found to be in good agreement with experiments.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. vii + 54 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 169
Keyword
Physics, Non-collinear magnetism, spin spirals, first principles, density functional theory, Fermi surfaces, electronic structure, f-electron systems, Fysik
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-6812 (URN)91-554-6540-4 (ISBN)
Public defence
2006-05-12, Siegbahnsalen, Ångström Laboratory, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2006-04-21 Created: 2006-04-21 Last updated: 2012-03-27Bibliographically approved

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Eriksson, OlleBergman, AndersNordström, Lars

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