Nanoscale imaging and control of antiferromagnetic domains and exchange bias in 2D magnetic multilayers

The interfacial exchange coupling between antiferromagnets (AFMs) and ferromagnets (FMs) has unlocked new functionalities in spintronic devices, enabling exchange bias effects and the control of resilient AFM states. In two-dimensional (2D) A-type AFMs, naturally connected even and odd layers form AFM-like and FM-like regions with nearly perfect lateral interfaces, leading to unique lateral interfacial effects. In this work, we leverage this new integration possibility alongside the cutting-edge magnetic imaging, scanning nitrogen-vacancy (NV) center magnetometry. Through high-sensitivity nanoscale imaging, we uniquely distinguish antiphase even-layer states and AFM domain walls by their weak, yet detectable, signals down to the bilayer limit. The lateral exchange coupling also enables manipulation of antiphase AFM states in even layers. Moreover, we demonstrate tunable exchange bias on odd layers through strategic manipulation of the surrounding even-layer states. Our nanoscale visualization uncovers the microscopic origins of exchange bias and introduces a highly-controlled and openly-characterizable platform for hybrid AFM-FM technologies.