Magneto-Transport and Optical Control of Magnetization in Organic Systems: From Polymers to Molecule-based Magnets
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2009
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu12529561972021-08-03T05:57:06Z Magneto-Transport and Optical Control of Magnetization in Organic Systems: From Polymers to Molecule-based Magnets Bozdag, Kadriye Deniz Physics Photoinduced magnetism room temperature magnet molecule-based magnet V-Cr Prussian Blue Analog polyaniline nanofiber network magnetoresistance temperature electric field morphology <p>Organic systems can be synthesized to have various impressive properties such as room temperature magnetism, electrical conductivity as high as conventional metals and magnetic field dependent transport. In this dissertation, we report comprehensive experimental studies in two different classes of organic systems, V-Cr Prussian blue molecule-based magnets and polyaniline nanofiber networks.</p> <p>The first system, V-Cr Prussian blue magnets, belongs to a family of cyano-bridged bi-metallic compounds which display a broad range of interesting photoinduced magnetic properties. A notable example for optically controllable molecule-based magnets is Co-Fe Prussian blue magnet (<i>T<sub>c</sub></i> ∼ 12 K), which exhibits light-induced changes in between magnetic states together with glassy behavior. In this dissertation, the first reports of reversible photoinduced magnetic phenomena in V-Cr Prussian blue analogs and the analysis of its AC and DC magnetization behavior are presented. Optical excitation of V-Cr Prussian blue, one of the few room temperature molecule-based magnets, with UV light (λ = 350 nm) suppresses magnetization, whereas subsequent excitation with green light (λ = 514 nm) increases magnetization. The partial recovery effect of green light is observed only when the sample is previously UV-irradiated. Moreover the photoinduced state has a long lifetime at low temperatures (<i>t</i> > 10<sup>6</sup> s at <i>T</i> = 10 K) indicating that V-Cr Prussian blue reaches a hidden metastable state upon illumination with UV light. The effects of optical excitation are maintained up to 200 K and completely erased when the sample is warmed above 250 K. Results of detailed magnetic studies and the likely microscopic mechanisms for the photo illumination effects on magnetic properties are discussed.</p> <p>The second organic system, polyaniline nanofiber networks, was synthesized via dilute polymerization and studied at low and high electric and magnetic fields for temperatures 2 K - 250 K for their magneto-transport behavior. We observed large magnetoresistance (up to 55 % at <i>H</i> = 8 T and <i>T</i> = 3 K) in polymer networks composed of nanofibers with an average diameter of about 80 nm. A crossover from positive MR to negative MR is observed at ∼ 87 K. The positive and negative MR are attributed to two competing mechanisms; shrinkage of the localized electron wavefunction and suppression of quantum interference of electron wavefunctions propagating along different current paths in the hopping process by the applied magnetic field. In addition to temperature dependence of magnetoresistance, dependencies on morphology of the nanofibers and applied electric field are observed. Detailed DC electrical transport results of various polyaniline nanober samples and possible mechanisms responsible for the magneto-transport behavior are discussed.</p> 2009-09-30 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1252956197 http://rave.ohiolink.edu/etdc/view?acc_num=osu1252956197 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
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NDLTD |
| language |
English |
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NDLTD |
| topic |
Physics Photoinduced magnetism room temperature magnet molecule-based magnet V-Cr Prussian Blue Analog polyaniline nanofiber network magnetoresistance temperature electric field morphology |
| spellingShingle |
Physics Photoinduced magnetism room temperature magnet molecule-based magnet V-Cr Prussian Blue Analog polyaniline nanofiber network magnetoresistance temperature electric field morphology Bozdag, Kadriye Deniz Magneto-Transport and Optical Control of Magnetization in Organic Systems: From Polymers to Molecule-based Magnets |
| author |
Bozdag, Kadriye Deniz |
| author_facet |
Bozdag, Kadriye Deniz |
| author_sort |
Bozdag, Kadriye Deniz |
| title |
Magneto-Transport and Optical Control of Magnetization in Organic Systems: From Polymers to Molecule-based Magnets |
| title_short |
Magneto-Transport and Optical Control of Magnetization in Organic Systems: From Polymers to Molecule-based Magnets |
| title_full |
Magneto-Transport and Optical Control of Magnetization in Organic Systems: From Polymers to Molecule-based Magnets |
| title_fullStr |
Magneto-Transport and Optical Control of Magnetization in Organic Systems: From Polymers to Molecule-based Magnets |
| title_full_unstemmed |
Magneto-Transport and Optical Control of Magnetization in Organic Systems: From Polymers to Molecule-based Magnets |
| title_sort |
magneto-transport and optical control of magnetization in organic systems: from polymers to molecule-based magnets |
| publisher |
The Ohio State University / OhioLINK |
| publishDate |
2009 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1252956197 |
| work_keys_str_mv |
AT bozdagkadriyedeniz magnetotransportandopticalcontrolofmagnetizationinorganicsystemsfrompolymerstomoleculebasedmagnets |
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1719428350019108864 |