Spintronics has emerged as a promising field for next-generation devices, offering functionalities beyond complementary metal-oxide semiconductor (CMOS). A critical challenge in spintronics is to develop systems that can efficiently generate spin currents and enable their long-distance transport. Here, we demonstrate a graphene (Gr) / heavy-metal (HM) heterostructure system that combines strong charge-spin interconversion efficiency, induced by the spin Hall effect, with a long spin diffusion length. By employing an industry-friendly magnetron-sputtering technique, we deposit HM layers onto few-layer Gr while minimizing structural damage. The proximity effect from the HM enhances the spin Hall angle of Gr while limiting the reduction in its spin diffusion length. Additionally, the spin Hall angle can be tuned via an applied gate voltage, offering high controllability of the system. Importantly, these properties are observed across heterostructures composed of different HMs, indicating the generality of this approach. Our findings establish Gr/HM heterostructures as a scalable and versatile platform for spin current generation, paving the way for advanced spintronic devices with high efficiency, long spin propagation, and straightforward fabrication processes.

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• Spin Hall effect
• Spin current
• Spin diffusion
• Graphene
• Heterostructures
• Transition metals
• van der Waals systems
• Finite-element method