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

Direct link
Cite
Citation style
  • apa
  • 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
Microscopic picture of Co clustering in ZnO
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Materials Science, Materials Theory.
Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.
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, Materials Theory.
Show others and affiliations
2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 79, no 12, 125202- p.Article in journal (Refereed) Published
Abstract [en]

Density functional theory was applied to study the chemical and magnetic interactions between Co atoms doped in ZnO. It was found that the Co impurities tend to form nanoclusters and the interactions between these atoms are antiferromagnetic within the local spin-density approximation (LSDA)+Hubbard U approach. The extracted interatomic exchange parameters agree reasonably well with recent experimental results. We have analyzed and compared the electronic structure obtained using the LSDA and LSDA+U approaches and found that the LSDA+U gives the most reasonable result, highlighting the importance of short-ranged antiferromagnetic interactions due to superexchange.

Place, publisher, year, edition, pages
The American Physical Society , 2009. Vol. 79, no 12, 125202- p.
Keyword [en]
antiferromagnetic materials, cobalt, density functional theory, II-VI semiconductors, magnetic semiconductors, metal clusters, superexchange interactions, wide band gap semiconductors, zinc compounds
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-119891DOI: 10.1103/PhysRevB.79.125202ISI: 000264769300047OAI: oai:DiVA.org:uu-119891DiVA: diva2:301210
Available from: 2010-03-02 Created: 2010-03-02 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Density Functional Theory Applied to Materials for Spintronics
Open this publication in new window or tab >>Density Functional Theory Applied to Materials for Spintronics
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The properties of dilute magnetic semiconductors have been studied by combined ab initio, Monte Carlo, and experimental techniques. This class of materials could be very important for future spintronic devices, that offer enriched functionality by making use of both the spin and the charge of the electrons. The main part of the thesis concerns the transition metal doped ZnO.

The role of defects on the magnetic interactions in Mn-doped ZnO was investigated. In the presence of acceptor defects such as zinc vacancies and oxygen substitution by nitrogen, the magnetic interactions are ferromagnetic. For dilute concentrations of Mn (~ 5%) the ordering temperature of the system is low, due to the short ranged character of the exchange interactions and disorder effects.

The clustering tendency of the Co atoms in a ZnO matrix was also studied. The electronic structure, and in turn the magnetic interactions among the Co atoms, is strongly dependent on the exchange-correlation functional used. It is found that Co impurities tend to form nanoclusters and that the interactions among these atoms are antiferromagnetic within the local spin density approximation + Hubbard U approach.

The electronic structure, as well as the chemical and magnetic interactions in Co and (Co,Al)-doped ZnO, was investigated by joined experimental and theoretical techniques. For a good agreement between the two, approximations beyond the local density approximation must be used. It is found that the Co atoms prefer to cluster within the semiconducting matrix, a tendency which is increased with Al co-doping. We envision that it is best to describe the system as superparamagnetic due to the formation of  Co nanoclusters within which the interactions are antiferromagnetic.

The magnetic anisotropy and evolution of magnetic domains in Fe81Ni19/Co(001) superlattices were investigated both experimentally, as well as using model spin dynamics. A magnetic reorientation transition was found.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2010. 67 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 721
Keyword
spintronics, dilute magnetic semiconductors, density functional theory, exchange interactions, magnetic percolation, ordering temperature, disorder, electronic structure
National Category
Physical Sciences
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-119887 (URN)978-91-554-7737-0 (ISBN)
Public defence
2010-04-16, Polhemsalen, 751 20 Uppsala, Ångström Laboratory, 10:15 (English)
Opponent
Supervisors
Available from: 2010-03-26 Created: 2010-03-02 Last updated: 2010-03-26Bibliographically approved
2. Theoretical Studies of Magnetism and Electron Correlation in Solids
Open this publication in new window or tab >>Theoretical Studies of Magnetism and Electron Correlation in Solids
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work presents new development and applications of ab-initio simulation tools for material science. Focus lies on materials with strong electronic correlation and strong spin-orbit coupling. Improvements on methods for solving the impurity problem in LDA+DMFT is presented, as well as a reliant method for charge self-consistency in a LMTO based electronic structure code. A new adaptive scheme for Brillouin zone integration is developed, where we show a strong reduction of numerical noise compared to standard techniques. A reformulation of the standard LDA+U method aiming to reduce the number of free parameters is introduced. Fast and realistic reduction of the number of free parameters provides the possibility of high throughput calculations and enabled us to study a large number of compounds. An analysis method for polarization in terms of coupled multipoles, and their corresponding energy contributions is developed and applied. This led to the formulation of Katt's rules, a set of rules complementary to Hund's rules. Katt's rules applies for occupying the orbitals of an electronic shell with strong spin-orbit coupling. The analysis is also used to investigate the unconventional Uranium based superconductors URu2Si2, UPt3, UPd2Al3 and UNi2Al3, as well as the high temperature superconductor LaOFeAs. We also investigate the non-magnetic delta-phase of Plutonium, providing insight to the electronic structure and the branching ratios of 4d to 5f transitions seen in photo emission spectra.The influence of surface reconstruction on the magneto crystalline anisotropy is investigated in multilayer Fe/ZnSe, showing that Fe deposited on an unreconstructed interface strongly reduces the uniaxial component of the MAE. We provide a detailed understanding of the magnetic properties of Fe2P, opening possible routes for enhancing the MAE in this system. A general route to strong MAE in nano-laminates is presented, we apply this to propose a candidate with extremely strong anisotropy energy density, 5Fe/2W1-xReX for x=[0.6-0.8].

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. xii+70 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 920
Keyword
Magnetism, Superconductivity, Electron Correlation, DMFT, DFT, Actinides, multipoles, hidden order, magnetic anisotropy
National Category
Condensed Matter Physics
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-172334 (URN)978-91-554-8337-1 (ISBN)
Public defence
2012-05-22, Siegbahnsalen, Lägerhyddsv. 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Available from: 2012-04-26 Created: 2012-04-04 Last updated: 2012-08-01Bibliographically approved

Open Access in DiVA

No full text

Other links

Publisher's full text

Authority records BETA

Grånäs, OscarEriksson, OlleSanyal, Biplab

Search in DiVA

By author/editor
Grånäs, OscarEriksson, OlleSanyal, Biplab
By organisation
Materials Theory
In the same journal
Physical Review B. Condensed Matter and Materials Physics
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 435 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • 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