Zhixue Shu, Physics Graduate Student
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Abstract: The past few decades have witnessed a shift in the search for magnetism from bulk solids to low-dimensional systems, particularly van der Waals magnetic two-dimensional materials and their heterostructures. To fully exploit the potential of two-dimensional magnetism, it is essential to understand the magnetic properties of the corresponding bulk materials, including their ground states and excitations. Magnetization studies provide valuable insights into exchange interactions through spin stiffness and magnetic anisotropy through the spin wave excitation gap.
In the first part of this dissertation, the low-temperature magnetization of Cr-based magnetic insulators CrI3, CrSiTe3, and CrGeTe3 single crystals was systematically studied. The spin stiffness and spin excitation gap were extracted using Bloch’s law.
The second part of the dissertation explores the variation in the magnetic properties of the metallic van der Waals ferromagnet Fe3GeTe2 through continuous chemical composition tuning. We characterized both spin stiffness and the spin wave excitation gap across a spectrum of Fe3GeTe2 single crystals with varying Fe concentrations.
Additionally, we discovered and characterized a new layered ferromagnet. Single crystals of the new layered compound, Cr1.21Te2, were synthesized via a vapor transport method. The crystal structure and physical properties were characterized using single crystal and powder X-ray diffraction, temperature- and field-dependent magnetization, zero-field heat capacity, and angle-resolved photoemission spectroscopy. Spin-dependent band structure calculations were performed using density functional theory (DFT).