Investigation of Surface Oxidation States in Fe3GeTe2 via Ultrafast and Nonlinear Optical Technique

Abstract

Fe3GeTe2, with a high Curie temperature of about 200 K, is attracting attention as a next- generation spintronic material due to its interesting phenomena. However, the effect of surface oxidation on the electronic structure and magnetic properties of Fe3GeTe2 remains elusive. In this thesis, we investigated the influence of surface oxidation on the electronic, lattice, and magnetic dynamics in Fe3GeTe2 using various optical techniques. The oxidation was induced by annealing in ambient conditions. We found that the transient reflectivity and photo-induced demagnetization dynamics are significantly modified by surface oxidation. Additionally, the second harmonic generation (SHG) intensity has increased with oxidation. These results highlight the complex interaction among charge, spin, and lattice under surface oxidation. Our results suggest that oxidation serves as a crucial tuning parameter for controlling two-dimensional ferromagnetic materials. It offers insights into the design of spintronic devices based on Dzyaloshinskii-Moriya interaction or spin-orbit torque effects.