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Chemically Tailored Organic-Based Magnets to Exploit Optical Control of Magnetization and Depth-Resolved Magnetization in V[TCNE]x~2 via Polarized Neutron Reflectivity

Chen, Chia-Yi

Abstract Details

2010, Doctor of Philosophy, Ohio State University, Chemical Physics.

Organic-based magnets have attracted much attention in recent decades as numerous benefits of this class of materials have been touted. In particular, chemical tailorability and potential use in practical applications paint a promising picture for the future of organic-based magnets in the field of spintronics. In the first part of this work, chemically tailoring organic-based magnets with optical-controllable functionality is realized through modifying organic molecules with azo functional groups. Two new optical-switchable electron acceptors, 3,3’-di-(1,1,2-tricyanovinyl)azobenzene (DTCVAzo) and 3,-(1,1,2-tricyanovinyl)azobenzene (TCVAzo), were synthesized and characterized. Their associated organic-based magnets prepared from reaction with V(CO)6 exhibit magnetic ordering below 60 and 126 K, respectively. At low temperatures the magnetization of both magnets decreases upon illumination with UV light whereas no change in magnetization is observed with subsequent visible light irradiation. The reduced magnetization is a long-lived metastable state in the dark and at low temperatures (> 106 s at 15 K) but can be fully recovered by thermal treatment above 240 K. A further study was extended to a solid solution magnet prepared from the reaction of V(CO)6 and a mixture of tetracyanoethylene (TCNE) and TCVAzo. An interesting multi-step photomagnetic response is observed in the solid solution at low temperatures with the illumination of UV or visible light. The correlation between the photoinduced magnetization of the organic-based magnets and the photoisomerization of the azo functional groups was studied by UV-Vis absorption spectroscopy. The results suggest the photomagnetic effects are due to structural changes driven by the photoisomerization of the azo functional groups, leading to a different strength of magnetic exchange coupling.

The second focus of this work is to characterize the depth-resolved magnetization of thin films of the organic-based magnet, V[TCNE]x~2. Practical application of this material has been realized in spintronic devices, thus it is important to fully understand the chemical and magnetic properties throughout the films. Different thicknesses of V[TCNE]x~2 films prepared by chemical vapor deposition (CVD) were studied. Their bulk magnetizations show a thickness dependence at low magnetic field, suggesting stronger random magnetic anisotropy is present in the thicker film; however, this phenomenon disappears at sufficiently high fields. The depth profiles from polarized neutron reflectivity studies exhibit two sublayers in V[TCNE]x~2 film, which is ascribed to partial oxidation occurring in the top portion of the layer. Detailed analysis suggests the chemical and magnetic properties of V[TCNE]x~2 are homogeneous throughout the thickness of the film if there is no oxygen contamination.

Arthur Epstein, PhD (Advisor)
Ezekiel Johnston-Halperin, PhD (Committee Member)
Yiying Wu, PhD (Committee Member)
153 p.

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Citations

  • Chen, C.-Y. (2010). Chemically Tailored Organic-Based Magnets to Exploit Optical Control of Magnetization and Depth-Resolved Magnetization in V[TCNE]x~2 via Polarized Neutron Reflectivity [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1293405276

    APA Style (7th edition)

  • Chen, Chia-Yi. Chemically Tailored Organic-Based Magnets to Exploit Optical Control of Magnetization and Depth-Resolved Magnetization in V[TCNE]x~2 via Polarized Neutron Reflectivity. 2010. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1293405276.

    MLA Style (8th edition)

  • Chen, Chia-Yi. "Chemically Tailored Organic-Based Magnets to Exploit Optical Control of Magnetization and Depth-Resolved Magnetization in V[TCNE]x~2 via Polarized Neutron Reflectivity." Doctoral dissertation, Ohio State University, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=osu1293405276

    Chicago Manual of Style (17th edition)