2024 Theses Doctoral

Exploring the Magnetic and Electronic Properties of van der Waals Materials

Han, Sae Young

This dissertation provides a comprehensive exploration of the synthesis and properties of van der Waals materials for two-dimensional applications. We delve into the unique characteristics of these materials, which are composed of layers bound by weak van der Waals forces, in contrast to strong covalent or ionic bonds. Their layered structure allows for mechanical exfoliation, leading to the isolation of a monolayer or few-layer flakes. These structures retain the intrinsic properties of the bulk material while also exhibiting novel characteristics due to their reduced dimensionality.

Chapter 1 briefly introduces van der Waals materials and their advantageous characteristics for 2D applications. It also provides a brief history of the discovery of atomically thin magnetic materials and their applications.

Chapters 2 and 3 discuss the synthesis and characterization of a layered metallic antiferromagnet, TaFe1.14Te3. Using a combination of magnetic, electronic, and transport measurements supported by first-principles DFT calculations, we investigate the interplay between the magnetic and electronic properties in the layered van der Waals magnet.

Chapter 4 explores a magnetic van der Waals semiconductor, KMnBi. KMnBi is part of the alkali metal manganese pnictide systems and is predicted to be a near-room temperature antiferromagnet and a small-gap semiconductor.

Chapter 5 discusses the interplay between molecular symmetry and broad-band chiral absorbance in a series of [6]helicenes for practical chiroptical applications.

Finally, Chapter 6 discusses the synthesis and characterizations of a systematically doped allotrope of carbon, graphullerite. We explore both solid-state and solution intercalation studies and the effects on their physical properties.