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Near-edge x-ray absorption studies of Na-doped tetracyanoethylene films: A model system for the V(TCNE)x room-temperature molecular magnet
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
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2008 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 77, 054420- p.Article in journal (Refereed) Published
Abstract [en]

V(TCNE)x, with TCNE=tetracyanoethylene and x~2, is an organic-based molecular magnet with potential to be used in spintronic devices. With the aim of shedding light on the unoccupied frontier electronic structure of V(TCNE)x we have studied pristine TCNE and sodium-intercalated TCNE by near edge x-ray absorption fine structure (NEXAFS) spectroscopy as well as with theoretical calculations. Sodium-intercalated TCNE was used as a model system of the more complex V(TCNE)x and both experimental and theoretical results of the model compound have been used to interpret the NEXAFS spectra of V(TCNE)x. By comparing the experimental and theoretical C K-edge of pristine TCNE, the contributions from the various carbon species (cyano and vinyl) could be disentangled. Upon fully sodium intercalation, TCNE is n doped with one electron per molecule and the features in the C and N K-edge spectra of pristine TCNE undergo strong modification caused by partially filling the TCNE lowest unoccupied molecular orbital (LUMO). When comparing the C and N K-edge NEXAFS spectra of fully sodium-doped TCNE with V(TCNE)x, the spectra are similar except for broadening of the features which originates from structural disorder of the V(TCNE)x films. The combined results from the model system and V(TCNE)x suggest that the lowest unoccupied molecular orbital with density on the nitrogen atoms in V(TCNE)x has no significant hybridization with vanadium and is similar to the so-called singly occupied molecular orbital of the TCNE anion. This suggests that the LUMO of V(TCNE)x is TCNE or vanadiumlike, in contrast to the frontier occupied electronic structure where the highest occupied molecular orbital is a hybridization between V(3d) and cyano carbons. The completely different nature of the unoccupied and occupied frontier electronic structure of the material will most likely affect both charge injection and transport properties of a spintronic device featuring V(TCNE)x.

Place, publisher, year, edition, pages
Institutionen för teknik och naturvetenskap , 2008. Vol. 77, 054420- p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-11753DOI: 10.1103/PhysRevB.77.054420OAI: oai:DiVA.org:liu-11753DiVA: diva2:18187
Note
Original publication: E. Carlegrim, B. Gao, A. Kanciurzewska, M. P. de Jong, Z. Wu, Y. Luo and M. Fahlman, Near-edge x-ray absorption studies of Na-doped tetracyanoethylene films: A model system for the V(TCNE)x room-temperature molecular magnet, 2008, Physical Review B, (77), 054420. http://dx.doi.org/10.1103/PhysRevB.77.054420. Copyright: The America Physical Society, http://prb.aps.org/Available from: 2008-05-07 Created: 2008-05-07 Last updated: 2010-05-05
In thesis
1. Preparation and characterization of an organic-based magnet
Open this publication in new window or tab >>Preparation and characterization of an organic-based magnet
2007 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In the growing field of spintronics there is a strong need for development of flexible lightweight semi-conducting magnets. Molecular organic-based magnets are attractive candidates since it is possible to tune their properties by organic chemistry, making them so-called “designer magnets”. Vanadium tetracyanoethylene, V(TCNE)x, is particularly interesting since it is a semiconductor with Curie temperature above room temperature (TC~400 K). The main problem with these organic-based magnets is that they are extremely air sensitive. This thesis reports on the frontier electronic structure of the V(TCNE)x by characterization with photoelectron spectroscopy (PES) and near edge x-ray absorption fine structure (NEXAFS) spectroscopy. It also presents a new and more flexible preparation method of this class of organic-based thin film magnets. The result shows improved air stability of the V(TCNE)x prepared with this method as compared to V(TCNE)x prepared by hitherto used methods.

Place, publisher, year, edition, pages
Institutionen för teknik och naturvetenskap, 2007. 32 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1338
Keyword
Organic-based magnets, spintronics, photoelectron spectroscopy, near edge x-ray absorption fine structure spectroscopy, chemical vapor deposition, physical vapor deposition
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
urn:nbn:se:liu:diva-10426 (URN)978-91-85895-21-2 (ISBN)
Presentation
2007-12-07, Jordan-Fermi, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2008-01-07 Created: 2008-01-07 Last updated: 2009-04-09
2. Development of Organic-Based Thin Film Magnets for Spintronics
Open this publication in new window or tab >>Development of Organic-Based Thin Film Magnets for Spintronics
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the growing field of spintronics, development of semiconducting magnets is a high priority. Organic-based molecular magnets are attractive candidates since their properties can be tailor-made by organic chemistry. Other advantages include low weight and low temperature processing. Vanadium tetracyanoethylene, V(TCNE)x, x~2, is particularly interesting since it is one of very few semiconducting magnets with magnetic ordering above room temperature.

The aim of the research presented in this thesis was to prepare and characterize thin film organic-based magnets with focus on V(TCNE)x. Photoelectron and absorption spectroscopy studies were performed leading to a more complete picture of the electronic and chemical structure of the material. Depending on the preparation method of V(TCNE)x, the material contains varying amounts of disorder which among other things makes it very air sensitive. In this thesis, a new preparation method for organic-based magnets based on physical vapor deposition is presented and the first result shows that it generates less air sensitive V(TCNE)x than previous methods reported. A new spin valve design based on V(TCNE)x was proposed where the material delivers both spin-filtering and spin-transporting functionality, making use of its fully spin-polarized transport levels. In such devices, the interface of V(TCNE)x with ferromagnetic metals is of great importance and was hence studied. As vanadium ions always are very reactive towards oxygen, substituting vanadium by a less reactive ion would be desirable from both an interface engineering and device packaging perspective. Very few alternatives exist however that orders magnetically above room temperature. In order to find out what are the key design criteria for preparing thin film semiconducting room temperature magnets, we have begun to study systems which order magnetically much below room temperature and compared them with V(TCNE)x.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2010. 49 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1317
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-56262 (URN)978-91-7393-385-8 (ISBN)
Public defence
2010-05-25, Planck, Fysikhuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2010-05-05 Created: 2010-05-05 Last updated: 2010-05-05Bibliographically approved

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Carlegrim, ElinKanciurzewska, Annade Jong, Michel PFahlman, Mats

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