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Magnetic Interactions in Transition Metal Dichalcogenides

Avalos Ovando, Oscar Rodrigo
http://orcid.org/0000-0003-3572-7675
http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1540818398439166

Abstract Details

2018, Doctor of Philosophy (PhD), Ohio University, Physics and Astronomy (Arts and Sciences).
In this dissertation we study magnetic induced effects on semiconducting transition metal dichalcogenides, such as MoS2, WS2, and MoTe2. We model finite size structures, such as flakes, ribbons, and heteroribbons, with a suitable low energy three-orbital tight binding model, which considers the right symmetries at energies close to the band gap. We study magnetic interactions in different systems, such as between magnetic impurities in MoS2 flakes and MoS2-WS2 heteroribbons. Moreover, we consider a MoTe2 ribbon on top of a ferromagnetic insulator substrate to study magnetic exchange effects induced by proximity of the two materials. In the case of magnetic impurity systems, we study two different regimes: the effective exchange interaction between two magnetic impurities embedded in dichalcogenides, and the study of ground state configurations for many magnetic impurities. For the first regime, we study the indirect Ruderman-Kittel-Kasuya-Yosida exchange interaction, which describes how the magnetic impurity spins align with respect to each other. We find sizable non-collinear Dzyaloshinskii-Moriya interactions terms, along the typical Heisenberg and Ising terms. We also find long range interactions (slow decay) when the impurities are set on locations of high wave function probability, such as the flake edges and the interface of the heteroribbons, and at Fermi levels in the gap of the material. In the second regime, the study of multiple magnetic impurities in a spin chain arrangement shows the appearance of low energy ferromagnetic and helical phases, tunable by experimental parameters such as impurity separation and gating. In the hybrid system of MoTe2 on a ferromagnetic substrate, we find spin polarization and spin currents at the MoTe2 edge, driven by Rashba and exchange fields induced by the proximity of the substrate. Our results reveal that the effective magnetic exchange in a TMD finite sample results in strong spin-polarized edge states lying in the 2D bulk energy gap, and yet experimentally accessible through electrostatic gating. These edge states are extended along the borders of the TMD nanoribbon, resulting in spin-polarized currents that can be activated by shifting gate voltages. We note that our results rely on experimentally realistic parameters to reliable describe TMD structures. We further consider the tunability of gating, and spin manipulation via scanning tunneling microscopy, among others, as powerful possible probe of the fascinating behavior we describe here.
Sergio Ulloa, Ph.D. (Advisor)
Wojciech Jadwisienczak, Ph.D. (Committee Member)
Eric Stinaff, Ph.D. (Committee Member)
David Drabold, Ph.D. (Committee Member)
152 p.
Physics
2D materials; Transition metal dichalcogenides; MoS2; MoTe2; WS2; Magnetic interactions; RKKY interaction; Dzyaloshinskii-Moriya interaction; van der Waals

Recommended Citations

Citations

  • Avalos Ovando, O. R. (2018). Magnetic Interactions in Transition Metal Dichalcogenides [Doctoral dissertation, Ohio University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1540818398439166

    APA Style (7th edition)

  • Avalos Ovando, Oscar. Magnetic Interactions in Transition Metal Dichalcogenides. 2018. Ohio University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1540818398439166.

    MLA Style (8th edition)

  • Avalos Ovando, Oscar. "Magnetic Interactions in Transition Metal Dichalcogenides." Doctoral dissertation, Ohio University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1540818398439166

    Chicago Manual of Style (17th edition)

ohiou1540818398439166
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This open access ETD is published by Ohio University and OhioLINK.