Interfacial Topological Hall Effect as Sensitive Electrical Probe of Topological Spin Structures in Ultrathin Insulator

Topological Hall effects (THE) enable electrical detection of noncoplanar spin textures in conducting magnets, leaving insulating systems largely inaccessible. Here we introduce the interfacial topological Hall effect (ITHE), where the spin topology of an insulating magnet is imprinted onto an adjacent heavy metal via the magnetic proximity effect. We show that ITHE may yield a Hall-conductivity-to-magnetization ratio exceeding 2 V⁻¹, far surpassing conventional anomalous Hall scaling, demonstrating that interfacial spin transport couples more strongly to spin topology than to magnetization. ITHE also operates in ultrathin films with sub-nanometer spin textures, surpassing other probes of topological spin structures. Using ITHE, we uncover that topological spin structures can be exceptionally robust (in h-LuFeO₃, persisting up to 14 T, the highest field tested), in stark contrast to the fragility suggested by the peak-dip features in conventional THE. These results establish ITHE as a versatile probe of topological magnetism in insulating and low-dimensional systems.