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Preparation and characterization of an organic-based magnet
Linköping University, Department of Science and Technology. Linköping University, The Institute of Technology.
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 [en]
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: urn:nbn:se:liu:diva-10426ISBN: 978-91-85895-21-2 (print)OAI: oai:DiVA.org:liu-10426DiVA: diva2:17166
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
List of papers
1. Near-edge x-ray absorption studies of Na-doped tetracyanoethylene films: A model system for the V(TCNE)x room-temperature molecular magnet
Open this publication in new window or tab >>Near-edge x-ray absorption studies of Na-doped tetracyanoethylene films: A model system for the V(TCNE)x room-temperature molecular magnet
Show others...
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
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-11753 (URN)10.1103/PhysRevB.77.054420 (DOI)
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: 2017-12-13
2. The unoccupied electronic structure of the semi-conducting room temperature molecular magnet V(TCNE)2
Open this publication in new window or tab >>The unoccupied electronic structure of the semi-conducting room temperature molecular magnet V(TCNE)2
2008 (English)In: Chemical Physics Letters, ISSN 0009-2614, E-ISSN 1873-4448, Vol. 452, no 1-3, 173-177 p.Article in journal (Refereed) Published
Abstract [en]

The unoccupied electronic structure of the organic-based magnet V(TCNE)x (TCNE = tetracyanoethylene, x~2) has been studied with near edge x-ray absorption fine structure (NEXAFS) and with photoelectron spectroscopy (PES). By studying V(TCNE)x upon sodium-doping, the electron-accepting state, i.e. the lowest unoccupied molecular orbital (LUMO) of V(TCNE)x was shown mainly to be localized on (TCNE)--units in contrast to the hole-accepting state, i.e. the highest occupied molecular orbital (HOMO), which previously was assigned primarily to be V(3d)-derived. This study also showed that there are trap states for electron transport located below the (TCNE)2- level, likely leading to decreased electron mobility.

Place, publisher, year, edition, pages
Institutionen för teknik och naturvetenskap, 2008
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-11143 (URN)10.1016/j.cplett.2007.12.049 (DOI)
Note
Original publication: Elin Carlegrim, Anna Kanciurzewska, Michel P. de Jong, Carl Tengstedt and Mats Fahlman, The unoccupied electronic structure of the semi-conducting room temperature molecular magnet V(TCNE)2, 2008, Chemical Physics Letters, (452), 1-3, 173-177. http://dx.doi.org/10.1016/j.cplett.2007.12.049. Copyright: Elsevier Ltd, http://www.elsevier.com/Available from: 2008-02-27 Created: 2008-02-27 Last updated: 2017-12-13
3. Air-stable organic-based semiconducting room temperature thin film magnet for spintronics applications
Open this publication in new window or tab >>Air-stable organic-based semiconducting room temperature thin film magnet for spintronics applications
2008 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 92, no 16, 163308- p.Article in journal (Refereed) Published
Abstract [en]

Herein, we report on a preparation method of vanadium tetracyanoethylene, V(TCNE)x, an organic-based semiconducting room temperature thin film magnet. Previously, this compound has been reported to be extremely air sensitive but this preparation method leads to V(TCNE)x, which can retain its magnetic ordering at least several weeks in air. The electronic structure has been studied by photoelectron spectroscopy and the magnetic properties by superconducting quantum interference device. The properties mentioned above, in combination with complete spin polarization, makes this air-stable V(TCNE)x a very promising material for spintronic devices.

Place, publisher, year, edition, pages
Institutionen för teknik och naturvetenskap, 2008
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-11869 (URN)10.1063/1.2916901 (DOI)
Note
Original publication: Elin Carlegrim, Anna Kanciurzewska, Per Nordblad and Mats Fahlman, Air-stable organic-based semiconducting room temperature thin film magnet for spintronics applications, 2008, Applied Physics Letters, (92), 163308. http://dx.doi.org/10.1063/1.2916901. Copyright: American Institute of Physics, http://apl.aip.org/apl/top.jspAvailable from: 2008-05-21 Created: 2008-05-21 Last updated: 2017-12-13

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