Resistance Anomaly and Iterative Resistance Hysteresis in van der Waals Ferromagnet Fe3GeTe2

We report an intriguing anomaly in the longitudinal resistance (R_xx) of the oxidized van der Waals ferromagnet Fe₃GeTe₂ (FGT) at a zero magnetic field (B). This anomaly, observed within the ferromagnetic phase, appeared as a sharp increase in R_xx around 50 K. Notably, R_xx remained in this high-resistance state during the warming cycle and did not RESET even after the system transitioned into the paramagnetic phase, indicating an irreversible process. This behavior is attributed to the formation of weakly localized electronic states at the interface between the surface-oxidized antiferromagnetic layer and the underlying FGT. With successive thermal cycles (300–4 K), the magnitude of the resistance jump gradually diminished and was fully suppressed by the fourth run. In contrast, pristine, nonoxidized FGT flakes exhibited no such anomaly, confirming the crucial role of surface oxidation in modulating the resistance state. Additionally, measurements of R_xx as a function of magnetic field below the Curie temperature revealed possible combined effects of carrier localization, interfacial disorder, and trap-assisted conduction─particularly in the presence of surface oxidation and disorder in exfoliated FGT flakes─along with a pronounced increase in resistance near zero field. These observations point to the presence of localization sites at the oxide interface in oxidized FGT, offering valuable insights into electron transport behavior and potential applications in electronic and spintronic devices.