Robust Exchange Bias in van der Waals Heterostructures of Topological Insulators and Metallic Ferromagnets.

Exchange bias from ferromagnet (FM) and antiferromagnet (AFM) interface underpins modern spintronics and magnetic technologies. Van der Waals (vdW) magnets allow arbitrary stacking, offering richer material and device choices. However, challenges arise when integrating FM metals with vdW topological materials. Conductive channels from FMs obscure intrinsic topological transport properties of interest for low-dissipation spintronics. Here we report a device obtained by inserting an insulating h-BN spacer between FM Fe3GaTe2 and the AFM topological insulator MnBi2Te4, departing from the conventional requirement of direct FM/AFM contact. Contrary to expectations that a spacer would preclude coupling, we observe an exchange bias field of ∼0.5 T, among the highest in vdW magnetic systems. We propose that Fe3GaTe2 induces a ferromagnetic component on the MnBi2Te4 surface while its interior remains antiferromagnetic, resulting in exchange bias originating within MnBi2Te4 layers. This large exchange bias without direct contact opens new design avenues for vdW magnetic heterostructures and broadens the scope of low-dimensional magnetism.