Polarity-Reversal of Exchange Bias in van der Waals FePS/FeGaTe Heterostructures.

Exchange bias (EB) in antiferromagnetic (AFM)/ferromagnetic heterostructures is crucial for the advancement of spintronic devices and has attracted significant attention. The common EB effect in van der Waals heterostructures features a low blocking temperature (T) and a single polarity. In this work, a significant EB effect with a T up to 150 K is observed in FePS/FeGaTe heterostructures, and in particular, the EB exhibits an unusual temperature-dependent polarity-reversal behavior. Under a high positive field-cooling condition (e.g., μH ≥ 0.5 T), a negative EB field (H) is observed at low temperatures, and with increasing temperature, the H crosses zero at ≈20 K, subsequently becomes positive and later approaches zero again at T. A model composed of a top FePS/interfacial FePS/FeGaTe sandwich structure is proposed. The charge transfer from FeGaTe to FePS at the interface induces net magnetic moments (∆M) in FePS. The interface favors AFM coupling, and thus the reversal of ∆M of the interfacial FePS leads to the polarity-reversal of EB. Moreover, the EB can be extended to the bare FeGaTe region of the FeGaTe flake partially covered by FePS. This work provides opportunities for a deeper understanding of the EB effect and opens a new route toward constructing novel spintronic devices.