Isothermal tuning of exchange bias without field cooling in Fe3GeTe2/(Fe0.6Co0.4)5GeTe2 heterostructures

Exchange bias (EB) effect, emerging at the interface between ferromagnetic (FM) and antiferromagnetic (AFM) materials, plays a critical role in magnetic random-access memory by pinning the FM layer. Traditionally, the sign and magnitude of the exchange bias field (HEB) are established via field cooling. Here, we demonstrate isothermal control of HEB in van der Waals Fe3GeTe2/(Fe0.6Co0.4)5GeTe2 (FGT/FCGT) heterostructures by an asymmetric magnetic field sweep protocol, eliminating the need for field cooling. Without field cooling, sweeping from a large positive to a small negative field (or vice versa) generates a tunable HEB that scales with sweep asymmetry, reaching magnitudes up to ∼32 mT. Through magneto-optical Kerr effect microscopy measurement, we observe that the EB extends beyond the overlapped FGT/FCGT interface into bare FGT regions, indicating long-range collective domain pinning. This behavior is attributed to defect-induced spin polarization and the formation of non-equilibrium domain configurations in the A-type AFM FCGT. This field-cooling-free approach provides a low-power, reversible mechanism for manipulating interfacial magnetism, offering a simplified pathway toward reconfigurable van der Waals spintronic devices.