Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • 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
Ab initio Studies on Exchange Interactions in Metals and Correlated Oxides
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

A report is given on the implementation of a frozen magnon technique in the FLAPW code FLEUR, showing that the procedure reduced computational costs compared with a previously implemented method, while delivering accurate results. Furthermore a generalisation was made of the well known one lattice formula that connects the total energy differences of spin-spirals to the adiabatic magnon excitation energies to multiple lattice systems.

The implemented method was applied to B2 structured FeCo to investigate the changes of the Curie temperature with a tetragonal distortion and it was found that the FeCo films grown on Rh have characteristics that makes it a good candidate for HAMR storage media. The method was also applied to a selection of spin-gapless semiconductors in order to investigate their magnetic properties. It was found that all of the studied materials have a Curie temperature well above room temperature and excellent agreement with experimental results was obtained for the material Mn2CoAl that has been synthesised.

Finally, the implemented frozen magnon method was adjusted to include constraining fields to restrict the directions of the magnetic moments. It was shown that this procedure significantly improved the agreement between the dispersion for all considered spin-spiral configuration and introduced significant adjustments of the exchange parameters. However for other materials, such as bcc-Fe, such corrections yield worse results and, motivated by the need for a consistent method, we considered a self consistent spin-spiral based method to extract the exchange parameters from the inverse transverse static magnetic susceptibility. Preliminary results show that the newly implemented method gives results close to the corrected frozen magnon method for FeCo and results close to the uncorrected frozen magnon method for bcc Fe and thus provides a consistent improvement over the two previously used methods.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. , 53 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1236
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:uu:diva-246766ISBN: 978-91-554-9190-1 (print)OAI: oai:DiVA.org:uu-246766DiVA: diva2:794092
Public defence
2015-04-17, room 10132, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2015-03-26 Created: 2015-03-10 Last updated: 2015-04-17Bibliographically approved
List of papers
1. Exchange parameters and adiabatic magnon energies from spin-spiral calculations
Open this publication in new window or tab >>Exchange parameters and adiabatic magnon energies from spin-spiral calculations
2013 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 88, no 13, 134427- p.Article in journal (Refereed) Published
Abstract [en]

We present a method of extracting the exchange parameters of the classical Heisenberg model from first-principles calculations of spin-spiral total energies based on density functional theory. The exchange parameters of the transition-metal monoxides MnO and NiO are calculated and used to estimate magnetic properties such as transition temperatures and magnon energies. Furthermore we show how to relate the magnon energies directly to differences in spin-spiral total energies for systems containing an arbitrary number of magnetic sublattices. This provides a comparison between magnon energies using a finite number of exchange parameters and the infinite limit.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-211020 (URN)10.1103/PhysRevB.88.134427 (DOI)000326159000001 ()
Available from: 2013-11-20 Created: 2013-11-19 Last updated: 2017-12-06Bibliographically approved
2. Tuning the Curie temperature of FeCo compounds by tetragonal distortion
Open this publication in new window or tab >>Tuning the Curie temperature of FeCo compounds by tetragonal distortion
Show others...
2013 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 10, 102404- p.Article in journal (Refereed) Published
Abstract [en]

Combining density-functional theory calculations with a classical Monte Carlo method, we show that for B2-type FeCo compounds, tetragonal distortion gives rise to a strong reduction of the Curie temperature T-C. The T-C monotonically decreases from 1575K (for c/a = 1) to 940K (for c/a = root 2). We find that the nearest neighbor Fe-Co exchange interaction is sufficient to explain the c/a behavior of the T-C. Combination of high magnetocrystalline anisotropy energy with a moderate TC value suggests tetragonal FeCo grown on the Rh substrate with c/a = 1.24 to be a promising material for heat-assisted magnetic recording applications.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-211902 (URN)10.1063/1.4819773 (DOI)000324389700031 ()
Available from: 2013-12-03 Created: 2013-12-03 Last updated: 2017-12-06Bibliographically approved
3. First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors
Open this publication in new window or tab >>First-principles calculations of exchange interactions, spin waves, and temperature dependence of magnetization in inverse-Heusler-based spin gapless semiconductors
Show others...
2015 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 91, no 17, 174439Article in journal (Refereed) Published
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-246764 (URN)10.1103/PhysRevB.91.174439 (DOI)000355170300004 ()
Available from: 2015-03-10 Created: 2015-03-10 Last updated: 2017-12-04Bibliographically approved
4. Constraining fields, the magnetic force theorem and susceptibility calculations
Open this publication in new window or tab >>Constraining fields, the magnetic force theorem and susceptibility calculations
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-246765 (URN)
Available from: 2015-03-10 Created: 2015-03-10 Last updated: 2015-04-17

Open Access in DiVA

fulltext(982 kB)