Measuring Strain-Mediated Magnetoelectric Effects In Magnetically Self-Assembled Multiferroic Janus Nanofiber Chains: A Quest for New Techniques to Study Multiferroic Nanomaterials

Author

Bryan Lucas Chávez

Date of Award

Spring 2021

Document Type

Open Access Dissertation

Department

Physics and Astronomy

First Advisor

Thomas M. Crawford

Abstract

Bi-phasic composite multiferroics couple piezoelectric and magnetostrictive proper- ties via an interfacial strain, allowing for control of their magnetic properties with electric fields and vice versa. Nanofibers have a larger area-to-volume ratio than thin films and are not affected by substrate clamping, leading to a predicted magnetoelec- tric coupling an order of magnitude higher than those found in thin-film multiferroics. Nanofibers have potential applications in photonics, nanoelectronics, biosensing, and optoelectronics. This work focuses on measuring magnetoelectric effects in electro- spun nanofibers made of barium titanate (BaTiO₃) and cobalt ferrite (CoFe₂O₄). To transform the disordered as-spun mat of fibers into a functional architecture for devices, they are ground to various lengths with an average diameter of ∼800 nm, and then magnetically self-assembled in a polymer solution. Temperature-dependent magnetometry shows that cobalt ferrite and barium titanate are coupled, confirmed with an observed magnetization shift at ∼393 K. I studied the self-assembly of these fibers in an external magnetic field and observed that the fibers chain end-to-end with different dynamics compared to magnetic nanoparticles. Due to geometric and elec- trochemical effects, in-fluid chaining proved unsuccessful as an in-situ probe of the magnetoelectric coupling of these promising multiferroic nanomaterials. I successfully used a novel scattered magneto-optical Kerr effect geometry to probe voltage-induced changes in magnetization. The observed magnetoelectric effects show 50-110 Oe/V changes in coercivity, typically non-hysteretic behaviors, and “collapsing” hysteresis loops. In conclusion, I successfully tested new techniques to measure the magneto- electric effects in self-assembled multiferroic nanofiber aggregates.

Rights

© 2021, Bryan Lucas Chávez

Recommended Citation

Chávez, B. L.(2021). Measuring Strain-Mediated Magnetoelectric Effects In Magnetically Self-Assembled Multiferroic Janus Nanofiber Chains: A Quest for New Techniques to Study Multiferroic Nanomaterials. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/6264