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Role of defects on the magnetic interactions in Mn-doped ZnO
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics.
2007 (English)In: Physica status solidi. A, Applied research, ISSN 0031-8965, E-ISSN 1521-396X, Vol. 204, no 1, 53-60 p.Article in journal (Refereed) Published
Abstract [en]

Oxide based diluted magnetic semiconductors are highly controversial from the point of view of intrinsic ferromagnetism brought in by doping with transition metal ions. By ab-initio Korringa-Kohn-Rostoker-Coherent-Potential-Approximation (KKR-CPA) calculations in the framework of density functional theory, we have obtained the electronic structure and magnetic exchange interaction parameters of Mn-doped ZnO in the presence and absence of several types of defects. A weak antiferromagnetic exchange interaction is observed in pure Mn-doped ZnO in the dilute limit with an increase in the strength of interactions with increasing concentration of Mn. In the presence of donor defects, such as oxygen vacancies and interstitial Zn, the interactions remain antiferromagnetic whereas in case of acceptor defects like Zn vacancies and N substitution of O, ferromagnetic interactions are observed. We have used the ab-initio exchange parameters in Monte-Carlo simulations for calculating finite temperature properties. Due to the short ranged behavior of interactions and disorder effects, the Curie temperatures calculated from Monte Carlo simulations show moderate values, not exceeding 50 K when the Mn content is 5%.

Place, publisher, year, edition, pages
2007. Vol. 204, no 1, 53-60 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-119895DOI: 10.1002/pssa.200673004ISI: 000243787000006OAI: oai:DiVA.org:uu-119895DiVA: diva2:301218
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

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Sanyal, BiplabEriksson, Olle

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