Phosphorene, a monolayer of black phosphorus, has emerged as a promising candidate for spintronic applications due to its unique electronic and structural properties. Unlike graphene, which lacks a bandgap, or transition metal dichalcogenides (TMDCs) with their sizable bandgaps, phosphorene offers a tunable direct bandgap and strong anisotropic behavior. These characteristics, combined with its intrinsic spin-orbit coupling (SOC) and potential for long spin diffusion lengths, make it an attractive material for spin-based devices. This article explores phosphorene’s spintronic potential, focusing on spin-orbit coupling, spin transport, and proximity effects in heterostructures, while addressing challenges such as spin relaxation and comparing its performance with graphene and TMDCs.

Spin-orbit coupling is a critical factor in spintronics, as it influences spin relaxation and coherence. Phosphorene exhibits a moderate intrinsic SOC, which is stronger than that of graphene but weaker than that of TMDCs like MoS2. Theoretical studies predict that the SOC in phosphorene arises primarily from its puckered lattice structure, leading to a Rashba-type splitting of about 1 to 10 meV, depending on the strain and electric field applied. This intermediate SOC strength is advantageous, as it balances spin manipulation and coherence. Unlike TMDCs, where strong SOC can lead to rapid spin relaxation, phosphorene’s moderate SOC may enable longer spin lifetimes while still allowing for efficient spin control via external fields.

Spin transport in phosphorene is highly anisotropic due to its puckered honeycomb structure. Calculations suggest that the spin diffusion length in phosphorene can exceed 1 micrometer at room temperature along the armchair direction, while being significantly shorter along the zigzag direction. This anisotropy stems from differences in effective mass and SOC strength along the two principal crystal axes. Experimental measurements of spin transport in phosphorene are still limited, but recent studies using non-local spin valve geometries have demonstrated spin injection and detection with spin lifetimes on the order of nanoseconds. These values are comparable to or slightly better than those observed in graphene, where spin lifetimes typically range from hundreds of picoseconds to a few nanoseconds, depending on sample quality and substrate effects.

Proximity effects in phosphorene-based heterostructures offer additional avenues for spin manipulation. When phosphorene is coupled to high-SOC materials like TMDCs or topological insulators, the interfacial SOC can be significantly enhanced. For example, theoretical work indicates that a phosphorene/WSe2 heterostructure can exhibit a proximity-induced Rashba SOC as large as 20 meV, enabling efficient spin-to-charge conversion via the spin Hall effect. Similarly, coupling phosphorene to ferromagnetic insulators like CrI3 can induce exchange interactions, leading to spin splitting without the need for external magnetic fields. These proximity effects are particularly promising for designing low-power spintronic devices, where external field control is minimized.

Despite its potential, phosphorene faces several challenges in spintronic applications. Spin relaxation mechanisms, such as Elliot-Yafet and D’yakonov-Perel processes, are influenced by defects, phonons, and interfacial roughness. Phosphorene’s susceptibility to oxidation and environmental degradation further complicates spin transport measurements, as surface adsorbates can introduce additional scattering centers. Encapsulation with hexagonal boron nitride (hBN) has been shown to improve stability and reduce extrinsic spin relaxation, but achieving uniform, defect-free interfaces remains a technical hurdle. In comparison, graphene benefits from weaker SOC and higher crystalline quality, resulting in longer spin lifetimes in ideal conditions, while TMDCs suffer from strong SOC-induced spin relaxation but excel in spin-valley coupling applications.

Experimental progress in phosphorene spintronics has been steady but slower than for graphene or TMDCs due to material stability issues. Recent breakthroughs include the demonstration of spin-polarized current injection using ferromagnetic contacts and the observation of Hanle spin precession in few-layer phosphorene devices. These experiments confirm that spin information can propagate over micrometer-scale distances, albeit with significant anisotropy. On the theoretical front, first-principles calculations predict that strain engineering or electric gating can modulate phosphorene’s SOC and spin transport properties, offering a pathway to tailor its performance for specific applications. For instance, applying uniaxial strain along the armchair direction can enhance the Rashba SOC while maintaining a reasonable spin lifetime.

Comparing phosphorene with graphene and TMDCs highlights its unique position in the spintronics landscape. Graphene’s weak SOC limits its spin manipulation capabilities but allows for exceptionally long spin diffusion lengths in ultra-clean samples. TMDCs, on the other hand, provide strong SOC and valley-dependent spin polarization but suffer from short spin lifetimes due to rapid relaxation. Phosphorene strikes a balance between these extremes, offering tunable SOC and anisotropic spin transport that can be optimized through heterostructure design. Its compatibility with existing semiconductor fabrication techniques further enhances its practical appeal.

Looking ahead, the development of phosphorene-based spintronic devices will require advances in material synthesis, passivation techniques, and heterostructure integration. Theoretical models suggest that optimized phosphorene heterostructures could achieve spin lifetimes exceeding 10 nanoseconds under ideal conditions, rivaling the best-performing graphene devices. Experimental validation of these predictions will be crucial to unlocking phosphorene’s full potential. Additionally, exploring hybrid systems combining phosphorene with other 2D materials may yield novel functionalities, such as gate-tunable spin filters or spin-orbit torque devices.

In summary, phosphorene’s distinctive combination of anisotropic electronic properties, moderate spin-orbit coupling, and compatibility with proximity effects positions it as a compelling material for spintronics. While challenges related to stability and spin relaxation persist, ongoing experimental and theoretical efforts are steadily addressing these issues. As research progresses, phosphorene may carve out a niche in applications requiring a balance between spin coherence and manipulability, complementing graphene and TMDCs in the broader spintronics ecosystem.