Room-temperature high-efficiency spin injection via van der Waals tunnel contact.

Efficient and reliable spin injection at room temperature with scalability is crucial for spintronic applications but remains challenging. Direct ferromagnetic metal deposition on two-dimensional materials often leads to inefficient transparent contacts. Here, we introduce an indium buffer layer between ferromagnetic cobalt (Co) and graphene to establish high-efficiency van der Waals (vdW) tunnel contacts. This buffer layer facilitates a physisorption interface between Co and graphene with a well-defined vdW gap, which functions as an effective spin tunnel barrier. Through buffer layer thickness optimization, we achieved a room-temperature spin injection efficiency of approximately 25% in graphene, comparable to the best single-crystalline oxide-tunnel-barrier-based devices, alongside explicit nonlocal spin valve signals and Hanle spin precession. We further demonstrate the scalability of our approach through uniform performance across multi-channel graphene spin valves and its versatility by achieving efficient spin injection in semiconducting MoS2 with an average efficiency of about 19.7%. Our strategy offers a simple, cost-efficient, and industry-compatible method for future large-scale and efficient spintronic applications.