Magnetism control with enhanced hard magnetic temperature in heterostructures based on the van der Waals magnet Fe5GeTe2

The discovery of two-dimensional magnets with intrinsic ferromagnetic or antiferromagnetic orders has opened up promising prospects for exploring magnetism at the desired thickness, paving the way for novel spintronic applications. In practice, the manipulation of the magnetic state in van der Waals ferromagnets is highly demanding but remains a significant challenge. In this work, we demonstrate that the magnetic states of the ${\mathrm{Fe}}_{5}{\mathrm{GeTe}}_{2}$ (FGT)-based heterostructures can be substantially tuned through a natural oxidation process. During this process, the exchange bias effect is observed in the naturally oxidized FGT flakes, confirming the existence of exchange coupling between the ferromagnetic FGT layer and antiferromagnetic oxide layer. Through the exchange coupling, the formed oxide layer affects the magnetic ordering of the Fe1 sites and magnetic anisotropy, which is evidenced by the increment of hard magnetic temperature. Theoretical calculations shed light on the crucial role of the oxide layer in the magnetic state transitions. These results provide valuable insights into the understanding and manipulation of the emergent magnetic states, leading to significant advances in the realization of practical two-dimensional spintronics.