Portland State University. Department of Physics
Term of Graduation
Date of Publication
Doctor of Philosophy (Ph.D.) in Applied Physics
1 online resource (ix, 97 pages)
Layered two dimensional films have been a topic of interest in the materials science community driven by the intriguing properties demonstrated in graphene. Tunable layer dependent electrical and magnetic properties have been shown in these materials and the ability to grow in the hexagonal phase provides opportunities to grow isostructural stacked heterostructures. In this investigation, cobalt selenide (CoSe) and nickel selenide (NiSe) were grown in the hexagonal phase, which consist of central metal atoms that are natively ferromagnetic in bulk, hence providing the potential for interesting magnetic phases in thin film arrangements as well. These structures may play a role in future progress in materials science and computing as magnetic tunnel junction layers or in the realm of spintronic computing. Thin films of long-range order CoSe and NiSe were grown via atomic layer deposition (ALD) and characterized for their crystalline phase, surface qualities, and magnetic properties. Characterization yielded films of long-range order which displayed paramagnetic behavior. Density functional theory (DFT) was utilized to first model the underlying structures of these materials. The lattice constants calculated were in close agreement with the values determined via x-ray diffraction. Also, the magnetron values determined using DFT were within predictable errors to those determined from the SQUID data. Spin polarized charge density maps were generated to yield the possible mechanisms of magnetism within the samples. It was found that unpaired electrons tended to occupy the edges of the layered structures in both NiSe and CoSe. CoSe showed a much higher density at the terminal edges than NiSe. It is believed that unpaired electrons at the edges dominate the magnetic properties of these materials.
© 2020 Michael Adventure Hopkins
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Hopkins, Michael Adventure, "Investigation of Magnetism in Transition Metal Chalcogenide Thin Films" (2020). Dissertations and Theses. Paper 5607.