Spin Frustration and Unconventional Surface Spin Canting State in Van der Waals Ferromagnet/Antiferromagnet Heterostructures.

Atomically flat surfaces of van der Waals (vdW) materials pave an avenue for addressing a long-standing fundamental issue of how a compensated antiferromagnet (AFM) surface frustrates a ferromagnetic (FM) overlayer in FM/AFM heterostructures. We investigate FeGeTe/NiPS vdW heterostructures by characterizing AFM and FM spins separately. We find that in-plane zig-zag AFM NiPS develops three equivalent AFM domains, which are robust against external magnetic field and magnetic coupling with FeGeTe.