Date of Award

2022-05-01

Degree Name

Master of Science

Department

Physics

Advisor(s)

Srinivasa R. Singamaneni

Abstract

The discovery of long-range magnetic ordering in ultrathin transition metal-based compounds shows great promise for the development of nanoscale memory and spintronic devices. Composed of cost-effective materials and boasting from strong chemical and thermal stability at low dimensions, van der Waals (vdW) ternary transition metal chalcogenide magnets like CrSiTe3 (CST), Fe2.7GeTe2 (FGT), and Mn3Si2Te6 (MST), provide not only possible energy solutions, but also a broad platform to explore the versatile magnetic character of this family of compounds. Although they have great potential, it has been found that their long-range magnetic ordering exists at temperatures far too low (the highest of these is for FGT, TC ~ 153 K) to be used in practical applications. Therefore, there is a big push toward finding ways of improving their magnetic characteristics at room temperature. Understanding and targeting the inner mechanisms governing the magnetism in these systems is a crucial step towards creating more effective functional devices. To these ends, we have employed non-destructive proton irradiation to enhance the magnetic properties of CST and MST and explored its effects on the bulk magnetization and Curie temperature as a function of magnetic field and irradiation fluence up to 1018 protons per unit area (H+/cm2). Further analysis on the magnetocrystalline anisotropy and magnetic entropy of the proton irradiated systems also serve to uncover the effects of mechanical perturbations on their intrinsic exchange mechanisms, which may prove useful for improving the functionality of these compounds as they are scaled to the two-dimensional level.The versatility of vdW systems is highlighted through the proton irradiation studies; thus, we move to explore a more invasive method of enhancement involving the electrochemical intercalation of organic tetrabutylammonium cations into the vdW gap of our compounds. We again explore the changes in the magnetization, magnetic anisotropy, and Curie temperature resulting from this process and find novel high-temperature features. Most notably, we confirm the presence of ferromagnetism up to 350 K in intercalated FGT. Spectroscopy data eliminate the possibility of crystal structure damage as the source of this effect; therefore, we look towards temperature-dependent Raman spectroscopy, spin-phonon coupling, and theoretical calculations for an explanation. From these experiments, we explore the possibility of a charge transfer effect and the role of modifications to the electronic structure of vdW magnets as an explanation to the observed changes. This study explores the different interactions within FGT and the processing methods that may lead to achieving robust room-temperature magnetism for applications.

Language

en

Provenance

Received from ProQuest

File Size

63 p.

File Format

application/pdf

Rights Holder

Hector Iturriaga

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