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Title: Exploring the Spin State of Cobalt in Oxide Perovskites
Authors: Oey, Yuzki
Advisors: Cava, Robert
Department: Chemistry
Certificate Program: Materials Science and Engineering Program
Class Year: 2019
Abstract: Controlling the spin state of a magnetic ion is important in the growing market of spintronic devices. The temperature dependent low spin to high spin transition of Co\(^{3+}\) in LaCoO\(_{3}\) has been commonly studied, but the factors that determine the spin state of Co\(^{2+}\) and Co\(^{3+}\) in a particular environment are unclear. In attempt to induce a spin state transition of these ions, Co\(^{2+}\) and Co\(^{3+}\) were introduced in small amounts in various cubic and orthorhombic perovskites SrTiO\(_{3}\), LaAlO\(_{3}\), CaSnO\(_{3}\), SrSnO\(_{3}\), and BaSnO\(_{3}\). Here I report that 4% doping of Co into SrTiO\(_{3}\) shows a high spin state of Co\(^{2+}\) but an intermediate spin state of Co\(^{3+}\) with a graduate decrease of effective moment as the cobalt oxidation state is increased from +2 to +3. In a system of LaAlO\(_{3}\)–SrTiO\(_{3}\) doped with 5% Co\(^{3+}\), LaAl\(_{0.95}\)Co\(_{0.05}\)O\(_{3}\) is nonmagnetic, but a mixture of 70% LaAlO\(_{3}\) and 30% SrTiO\(_{3}\) shows a high spin state of Co\(^{3+}\). Finally, the effect of M-O bond length on the spin state of Co\(^{3+}\) was examined by doping 10% Co\(^{3+}\) into ASnO\(_{3}\) (A = Ca, Sr, and Ba). While CaSn\(_{0.8}\)Co\(_{0.1}\)Nb\(_{0.1}\)O\(_{3}\) showed Co\(^{3+}\) in intermediate spin, increasing the cation size to Ba induced a high spin state. The work presented in this thesis shows the effect of crystal structure, such as M-O bond length, on the spin state of Co\(^{2+}\) and Co\(^{3+}\). Future work would provide further understanding of factors that determine the spin state of Co ions, allowing for more targeted spintronic materials to be made for various electronic device applications.
Type of Material: Princeton University Senior Theses
Language: en
Appears in Collections:Chemistry, 1926-2019

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