uu.seUppsala University Publications
Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Magnetic and Structural Properties of f-electron Systems from First Principles Theory
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials 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: urn:nbn:se:uu:diva-109639ISBN: 978-91-554-7644-1 (print)OAI: oai:DiVA.org:uu-109639DiVA: diva2:273570
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
List of papers
1. Crystal and magnetic structure investigation of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0): Experiment and theory
Open this publication in new window or tab >>Crystal and magnetic structure investigation of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0): Experiment and theory
Show others...
2006 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 74, no 9, 094419- p.Article in journal (Refereed) Published
Abstract [en]

The effect of Cu substitution on the structural and magnetic properties of TbNi5-xCux (x=0,0.5,1.0,1.5,2.0) have been investigated by x-ray diffraction, magnetization measurements and neutron powder and single crystal diffraction. The electronic and the magnetic structures of TbNi5 were studied using first principles theory. All samples were found to have the CaCu5-type structure, space group P6/mmm. The lattice parameters increase monotonically with increasing Cu concentration. The Curie temperature T-c has a maximum value of 29 K at x=1.0. The magnetic structure of TbNi5 at 10 K is incommensurate with a helimagnetic component [wave vector q similar to 2 pi/c(0,0,0.02)] perpendicular to a ferromagnetic one. In contrast, the substituted TbNi5-xCux alloy is ferromagnetic. All magnetic moments are observed to be located on the Tb atoms. The magnetocrystalline anisotropy in the ab plane is observed to be strongly increased by the Cu substitution, whereas the magnetization decreases with the Cu concentration. The observed magnetic structure of TbNi5 is consistent with first principles calculations regarding both the magnetic moments and the helimagnetic structure. The microscopical origin of the helimagnet is analyzed and correlated to the Fermi surface topology.

National Category
Inorganic Chemistry Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-82093 (URN)10.1103/PhysRevB.74.094419 (DOI)000240871700046 ()
Available from: 2006-09-18 Created: 2006-09-18 Last updated: 2011-06-01Bibliographically approved
2. Coupling between the 4f core binding energy and the 5f valence band occupation of elemental Pu and Pu-based compounds
Open this publication in new window or tab >>Coupling between the 4f core binding energy and the 5f valence band occupation of elemental Pu and Pu-based compounds
2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 78, no 24, 245101- p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate that there is a close coupling between 4f core binding energy and 5f valence band occu- pation for Pu-based materials. This enables accurate determination of the valence occupation of this class of materials by simply measuring the 4f core binding energy. Our study demonstrates that all allotropes of elemental Pu have a 5f occupation close to 5, a finding which is inconsistent with several of the current theoretical models attempting to describe this unique element. A few of the theoretical models proposed for this material are however consistent with our finding; a fact which is discussed in detail.

Keyword
binding energy, density functional theory, plutonium, plutonium compounds, valence bands
National Category
Condensed Matter Physics
Research subject
Solid State Physics
Identifiers
urn:nbn:se:uu:diva-109607 (URN)10.1103/PhysRevB.78.245101 (DOI)000262246400013 ()
Available from: 2009-10-20 Created: 2009-10-20 Last updated: 2012-03-17Bibliographically approved
3. Dynamical stabilization of the body centered cubic phase in lanthanum and thorium by phonon–phonon interaction
Open this publication in new window or tab >>Dynamical stabilization of the body centered cubic phase in lanthanum and thorium by phonon–phonon interaction
Show others...
2009 (English)In: Journal of Physics: Condensed Matter, ISSN 0953-8984, E-ISSN 1361-648X, Vol. 21, no 17, 175402- p.Article in journal (Refereed) Published
Abstract [en]

A recently developed self-consistent ab initio lattice dynamical method has been applied to the high temperature body centered cubic (bcc) phase of La and Th, which are dynamically unstable at low temperatures. The bcc phase of these metals is found to be stabilized by phonon–phonon interactions. The calculated high temperature phonon frequencies for La are found to be in good agreement with the corresponding experimental data.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-109608 (URN)10.1088/0953-8984/21/17/175402 (DOI)000264779900015 ()
Available from: 2009-10-20 Created: 2009-10-20 Last updated: 2012-04-01Bibliographically approved
4. Self-interaction correction scheme for a full-potential linear muffin-tin orbital method
Open this publication in new window or tab >>Self-interaction correction scheme for a full-potential linear muffin-tin orbital method
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

The self-interaction correction has been implemented in a full-potential linear muffin-tin orbital (FP-LMTO) scheme. The method is tested on several known materials where self-interaction is important; transition metal oxides and rare-earth elements. We find in general good agreement with previous implementations based on the atomic-sphere approximation. The implementation can be used for an crystal structure, without geometrical constraints. In addition, it is possible to consider non-spherical components to the electron density, which in self-interaction corrected electronic structure methods poses a particularly challenging problem, which is analyzed in detail.

Identifiers
urn:nbn:se:uu:diva-109681 (URN)
Available from: 2009-10-21 Created: 2009-10-21 Last updated: 2012-03-18
5. Theoretical investigation of the volume collapse of CeOFeAs under pressure
Open this publication in new window or tab >>Theoretical investigation of the volume collapse of CeOFeAs under pressure
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We conduct a density functional theory study of the high TC superconductor CeOFeAs using the self-interaction corrected local density approximation (LDA-SIC). We find that under compression the compound undergoes a transition from localized to delocalized Ce 4f -states at a pressure close to the experimentally observed point of vanishing superconductivity. This suggests that the observed abruptly vanishing superconductivity under pressure may have its origin in a Mott transition of the 4f electrons of the CeO layer.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-109673 (URN)
Available from: 2009-10-21 Created: 2009-10-21 Last updated: 2012-03-18
6. Adaptive smearing for Brillouin zone integration
Open this publication in new window or tab >>Adaptive smearing for Brillouin zone integration
(English)Manuscript (preprint) (Other (popular science, discussion, etc.))
Abstract [en]

We suggest a simple scheme for automatically determining the witdth parameter of smearing methods of the Brillouin zone integration in electronic structure calculation. The scheme retains one free parameter that at any time can be eliminated by choosing a denser k-space mesh until the desired accuracy is obtained. Tests are carried out in the context of Methfessel-Paxton smearing. This adaptive Gaussian smearing (AGS) is easily implemented, variational with respect to partial occupancies and free from spurious occupancies that are negative or larger than one. Its convergence properties are similar to those obtained with the modified tetrahedron method for energy resolution of ≥ 0 .1 meV.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-109678 (URN)
Available from: 2009-10-21 Created: 2009-10-21 Last updated: 2012-04-03
7. Theoretical studies of the incommensurate magnetic structure of a heavy fermion system: CeRhIn5
Open this publication in new window or tab >>Theoretical studies of the incommensurate magnetic structure of a heavy fermion system: CeRhIn5
Show others...
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.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-109676 (URN)10.1103/PhysRevB.81.094433 (DOI)000276207300083 ()
Available from: 2009-10-21 Created: 2009-10-21 Last updated: 2012-03-26Bibliographically approved
8. Order–disorder induced magnetic structures of FeMnP0.75Si0.25
Open this publication in new window or tab >>Order–disorder induced magnetic structures of FeMnP0.75Si0.25
Show others...
2011 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 83, no 13, 134420Article in journal (Refereed) Published
Abstract [en]

We report on the synthesis and structural characterization of the magnetocaloric FeMnP0.75Si0.25 compound. Two types of samples (as quenched and annealed) were synthesized and characterized structurally and magnetically. We have found that minute changes in the degree of crystallographic order causes a large change in the magnetic properties. The annealed sample, with higher degree of order is antiferromagnetic with a zero net moment. The as-quenched sample has a net moment of 1.26 μB /f.u. and ferrimagnetic-like behavior. Theoretical calculations give rather large values for the Fe and Mn magnetic moments, both when occupied on the tetrahedral and pyramidal lattice site. The largest being the Mn moment for the pyramidal site reaches values as high as 2.8 μB /atom.

National Category
Natural Sciences Inorganic Chemistry Engineering and Technology
Research subject
Chemistry with specialization in Inorganic Chemistry; Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-109665 (URN)10.1103/PhysRevB.83.134420 (DOI)000291973200006 ()
Available from: 2009-10-21 Created: 2009-10-21 Last updated: 2016-04-19Bibliographically approved

Open Access in DiVA

fulltext(1325 kB)526 downloads
File information
File name FULLTEXT01.pdfFile size 1325 kBChecksum SHA-512
a0ca1746fde68e82e9173e4148abc0b11f225399b9c567da2b31454f309e23a202b5cd75e0d058cedcd1355874944210059ccb3f1d40a55af91ee09b9639794e
Type fulltextMimetype application/pdf
Buy this publication >>

By organisation
Materials Theory
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 526 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 918 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf