Fabrication and analysis of vanadium oxides and vanadium oxide based magnetic hybrid structures
Date
2021
Authors
Sutton, Logan, author
Wu, Mingzhong, advisor
de la Venta, Jose, committee member
Ross, Kathryn, committee member
Prieto, Amy, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Vanadium oxide films and vanadium oxide-based magnetic hybrid structures are fabricated using various techniques and studied optically, electrically, structurally, and magnetically for their potential applications into magnetic recording, room temperature refrigeration, and optical switches. The different types of behavior seen in the transitions of the vanadium oxide class of compounds can be altered and optimized according to desirable qualities for these applications. Several different techniques were used for the fabrication of vanadium oxide-ferromagnetic (FM) composites with the goal of causing magnetic coupling and the optimization of coupling between the vanadium oxide compound and the FM compound. The ball milling process was used as the primary step in formation of the composites, but was shown to be ineffective at causing coupling between the compounds if used alone. The addition of a sintering process was shown to successfully couple V2O3 and Ni, with an optimization of the process determined to be primarily dependent on temperature. Optimized composites showed up to 56% changes in coercivity at the transition temperature of the V2O3. VO2 based composites were unable to be coupled due to problems with the reduction and oxidation of the compounds involved, and a lack of diffusion. A sol-gel technique for the fabrication of VO2 layers was optimized for large transitional properties and refined for reproducibility. Magnetic hybrid structures formed from the sol-gel fabricated films were shown to have comparable properties to their sputtered counterparts. W doped films fabricated using the sol-gel technique, when compared to doping using a sputtering technique, were demonstrated to allow for larger control over the ideal doping range. Doping was shown to have negligible effect on the morphology of the films, but produced several W based impurities. Although doping produced expected shifts and decreases in the transitional electrical transport properties, there were also unexplained shifts in the absolute resistance for higher doping. Magnetic hybrid structures based on doped films still produced large changes in the magnetic properties of the FM layer, but these changes were shifted to lower temperatures and reduced. Transmission and reflection of VO2 films fabricated using different techniques were shown to have different qualitative and quantitative behaviors at different optical wavelengths of incidence. Most films were shown to have downward switching in both the transmission and reflection at the transition, however thinner films sometimes showed upward switching in the transmission. Downward bumps caused by interference were seen in the reflection at 980 nm, as well as at 635 nm for two other films. The model that was developed to try to reproduce this behavior is successful for 60% of the films, and able to reproduce all of the qualitative behaviors described. However the trends in the fitted refractive index do not help elucidate what physical mechanism is responsible for the differences seen between samples.