Unconventional Zero-Field-Cooling Exchange Bias in 2D Van der Waals Magnetic Heterostructures

Exchange bias (EB) in two-dimensional van der Waals (vdW) ferromagnetic (FM)/antiferromagnetic (AFM) heterostructures holds great potential for advancing the applications of spintronic devices thanks to their defect-free and atomically flat interfaces. Normally, a field-cooling process is needed to either trigger or sustain the EB effect. Here we report a sizable EB effect in the Fe3GaTe2/CrSBr vdW heterostructure in a zero-field cooling process. Remarkably, an exceptionally large EB field (HEB) of 130.1 mT was achieved in Fe3GaTe2/CrSBr at 5 K, even though the spin configuration in Fe3GaTe2 and CrSBr is orthogonally arranged. Additionally, the HEB of Fe3GaTe2/CrSBr exhibits pronounced nonmonotonic and asymmetric dependence on the cooling field, with the maximum values appearing at intermediate field strength. The EB is effectively tuned by the thickness of the FM layer relative to that of the AFM layer, identifying this ratio as an additional important governing parameter. Our work suggests an unconventional mechanism of EB in vdW heterostructures, providing an innovative route for fabricating low-power and robust 2D spintronic devices.