Effect of magnetic tunneling layer in van der Waals Josephson Junction

Van der Waals (vdW) material has been attracted much attention recently because of their unique features including the accessibility to atomically thin and flat single-crystalline heterostructure. The two-dimensional (2D) nature of these heterointerfaces often enhances the quantum effect. Here, we report vdW ferromagnet can provide a unique opportunity to study the interplay of superconductivity and magnetism. We fabricated a ferromagnetic tunneling device consisting of vdW ferromagnet and superconductor. We observed that the devices exhibit Josephson coupling through magnetic tunneling across 1-6 atomic unit cell thick ferromagnetic insulating layers. Our observation is in contrast with the lack of Josephson coupling reported across traditional ferromagnetic insulating materials such as EuS. We also observed that our superconductor/ferromagnet hybrid devices show the hysteretic critical current against magnetic field sweep. The observed hysteresis differs from the one expected from the coercive field of the ferromagnet. Further study on magnetic structure and switching current distribution indicates the observed phenomena arisen from the interplay between magnetic domain and superconducting vortex structures.