Graphene has emerged as a promising material for spintronics due to its exceptionally long spin diffusion lengths and weak intrinsic spin-orbit coupling (SOC). These properties enable efficient spin transport over micrometer-scale distances at low temperatures, making it a candidate for spin-based logic and memory applications. However, achieving room-temperature operation remains a significant challenge, requiring precise control over spin relaxation mechanisms and SOC modulation.

The long spin diffusion lengths in graphene arise from its high crystal quality and low atomic number, which minimize spin scattering. Measurements using non-local spin valve geometries have demonstrated spin diffusion lengths exceeding 20 micrometers at cryogenic temperatures. These values are attributed to the dominance of Dyakonov-Perel spin relaxation, where momentum scattering suppresses spin decoherence. However, as temperature increases, additional mechanisms such as Elliott-Yafet scattering become significant, reducing spin lifetimes and diffusion lengths.

Hanle precession measurements are a critical tool for studying spin dynamics in graphene. By applying a perpendicular magnetic field, spins precess at the Larmor frequency, leading to damped oscillations in the non-local resistance. The resulting Hanle curves provide quantitative information on spin lifetime and diffusion coefficients. Studies have shown that spin lifetimes in graphene can reach several nanoseconds at low temperatures but drop sharply above 200 Kelvin due to enhanced phonon and impurity scattering.

Modulating spin-orbit coupling in graphene is essential for spintronic functionality. Intrinsic SOC in pristine graphene is weak, but it can be enhanced through several strategies. Proximity coupling to transition metal dichalcogenides (TMDs), such as tungsten disulfide (WS₂), induces Rashba-type SOC, splitting spin states by tens of millielectronvolts. Magnetic proximity effects, achieved by interfacing graphene with ferromagnetic insulators like yttrium iron garnet (YIG), further enable spin manipulation through exchange interactions. These hybrid structures demonstrate gate-tunable spin transport but face challenges in maintaining interfacial quality and minimizing spin scattering at elevated temperatures.

Spintronic device architectures leveraging graphene include lateral spin valves, spin-field-effect transistors (spin-FETs), and spin-orbit torque devices. Lateral spin valves utilize ferromagnetic electrodes to inject and detect spins, with graphene acting as the transport channel. While these devices exhibit high spin injection efficiencies at low temperatures, interfacial resistance and conductivity mismatch limit their room-temperature performance. Spin-FETs, which aim to modulate spin current via gate voltage, require strong and tunable SOC, making graphene-TMD heterostructures a leading candidate. However, achieving sufficient ON/OFF ratios remains difficult due to incomplete understanding of spin relaxation pathways.

Magnetic proximity effects introduce additional complexity. When graphene is placed near a ferromagnetic material, exchange coupling can polarize spins without an external magnetic field. This effect is useful for creating non-volatile spintronic memory elements. However, inhomogeneities in the magnetic layer and interfacial defects often lead to unpredictable spin scattering, degrading device performance. Recent studies suggest that van der Waals assembly of atomically sharp interfaces can mitigate these issues, but scalability and thermal stability remain unresolved.

Room-temperature operation is the primary challenge for graphene-based spintronics. While long spin diffusion lengths are achievable at cryogenic temperatures, thermal excitations drastically reduce spin coherence. Phonon-mediated scattering, defect-induced spin relaxation, and interfacial disorder all contribute to rapid spin dephasing above 200 Kelvin. Strategies to mitigate these effects include hexagonal boron nitride (hBN) encapsulation to suppress impurity scattering, as well as strain engineering to modify spin-phonon coupling. Nevertheless, no current approach has reproducibly achieved micrometer-scale spin transport at 300 Kelvin.

Another obstacle is the trade-off between SOC strength and spin lifetime. Enhancing SOC is necessary for spin manipulation but often accelerates spin relaxation. For example, heavy metal adatoms like gold or thallium can induce strong SOC but also introduce spin-scattering centers. Similarly, while TMD proximity layers enhance Rashba splitting, they may also increase intervalley scattering, reducing spin lifetimes. Balancing these competing effects requires precise material engineering, which has yet to be fully realized.

Future advancements depend on improving material quality and device design. Ultra-clean fabrication techniques, such as dry transfer methods for van der Waals heterostructures, can minimize interfacial defects. Additionally, exploring new hybrid materials, such as graphene coupled to topological insulators, may offer alternative pathways for spin control. Computational modeling of spin transport under realistic conditions could also guide experimental efforts by identifying optimal material combinations and device geometries.

In summary, graphene’s long spin diffusion lengths and tunable SOC position it as a key material for spintronics. Hanle precession measurements and proximity effects provide valuable insights into spin dynamics, while novel device architectures explore practical applications. However, room-temperature operation remains elusive due to unresolved challenges in spin relaxation and interfacial engineering. Overcoming these barriers will require interdisciplinary efforts in materials science, device physics, and computational modeling.