The positive exchange bias property with hopping switching behavior in van der Waals magnet FeGeTe

The magnetic exchange bias (EB) effect is one of the representative interlayer magnetic coupling phenomena and is widely utilized in numerous technological applications. However, its mechanism is still elusive even in a simple magnetic bilayered system because of the complex interface magnetic orders. Van der Waals (vdW) layered magnetic materials may provide an essential platform for deeply understanding the detailed mechanism of the EB owing to its ideal interface structure. Here we first observed the positive exchange-biased anomalous Hall effect with a hopping switching behavior in the FeGeTe vdW nano-flakes. After systemically studying the cooling field dependence properties of the EB effect, we propose that the coexistence of stable and frustrated surface magnetization of the antiferromagnetic (AFM) phase will modify the total interface coupling energy density between the ferromagnetic and AFM phases. This model could provide a consistent description for such unusual EB effect based on microspin simulation.