Magnetoresistance Effects in Emerging Two-dimensional Materials and Chiral Nanostructures

• Author / Creator

  Firouzeh, Seyedamin

• Spintronics, also known as "spin-based electronics," merges electronics and magnetism at the nanoscale and holds great promise for emerging quantum technologies and the next generation of data storage and sensing devices. Reducing the size of current spintronics devices with conventional magnetic materials presents a challenging task. To overcome these challenges, researchers are exploring several approaches, two of which will be investigated in this thesis.
  The first approach relies on the two-dimensional (2D) van der Waals (vdW) materials due to their mechanical flexibility and sensitivity to band structure and defect engineering. These properties make them attractive candidates for future spintronic applications with further miniaturization. Recently 2D magnetic materials have been discovered, which exhibit large magnetoresistance (MR) effects, albeit only at cryogenic temperatures, limiting their practicality. To further investigate this issue, this thesis focuses on vanadium diselenide (VSe2), a promising 2D material which has the potential for exhibiting room temperature ferromagnetism at the monolayer level. We have established a reproducible nanofabrication method to investigate thin flakes of this material in an out-of-plane geometry. We have observed significant positive linear MR effects (~60–70%) at room temperature, under a relatively small magnetic field range of 12kG. The MR originates due to the intrinsic inhomogeneity in the current-perpendicular-to-plane (CPP) transport path. Moreover, this phenomenon displays remarkable thermal stability and progressively enhances with rising temperatures.
  The second approach involves the use of chiral organic molecules, allowing us to exploit the so-called “chirality-induced spin selectivity” (CISS) effect in 1D and 2D systems. However, there are challenges in terms of feasibility, understanding, and reliable control of the phenomenon, especially in 1D and 2D systems, which are topics of much discussion and debate. In this regard, the general consensus is that spin–orbit coupling is an essential element needed to observe the CISS effect, but there is currently a lack of experimental evidence to support this claim. We studied the CISS effect in chiral functionalized 1D systems (carbon nanotubes (CNTs)) to investigate this claim. Additionally, transfer of CISS phenomenon from 1D to 2D materials is an uncharted avenue of research. We explore the CISS effect in 2D chiral graphene films and systematically investigate its properties under different conditions.
  Overall, we report new results which are relevant for future magnetic and spintronic devices. We also describe possible avenues of further investigations based on the results in this thesis.

• Subjects / Keywords

  • Spintronics
  • CISS
  • Graphene
  • VSe2
  • CNT
  • MR
  • Nanofabrication
  • Spin

• Graduation date

  Fall 2024

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-4t78-j112

• License

  This thesis is made available by the University of Alberta Library with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.