The phenomenon of induced magnetism in non-magnetic two-dimensional materials through proximity coupling to magnetic layers represents a significant advancement in the field of spintronics and quantum materials. This effect leverages the interaction between adjacent atomic layers to impart magnetic properties to otherwise non-magnetic systems, enabling novel functionalities in device applications. Among the most studied magnetic layers for such purposes is chromium triiodide (CrI3), a van der Waals material exhibiting intrinsic ferromagnetism at monolayer thickness. The proximity-induced magnetism in 2D materials opens pathways for spin filtering, exchange bias, and valley polarization, which are critical for next-generation electronic and optoelectronic devices.

Proximity coupling arises when a non-magnetic 2D material, such as graphene or a transition metal dichalcogenide (TMD), is placed in close contact with a magnetic layer. The electronic states of the non-magnetic material are perturbed by the exchange interaction from the adjacent magnetic layer, leading to induced spin polarization. For instance, graphene interfaced with CrI3 exhibits a measurable magnetic moment due to the hybridization of carbon pz orbitals with chromium d orbitals. The induced magnetism is highly sensitive to the interlayer distance and stacking configuration, making precise control over the heterostructure assembly crucial.

Exchange bias, a key manifestation of proximity-induced magnetism, occurs when the magnetic hysteresis loop of the coupled system shifts along the field axis due to interfacial exchange interactions. This effect is particularly pronounced in heterostructures where antiferromagnetic coupling exists between the magnetic layer and the induced moments in the 2D material. Exchange bias has been observed in graphene/CrI3 systems, with shifts in the hysteresis loop reaching up to several tens of millitesla at low temperatures. The magnitude of the exchange bias depends on interfacial spin alignment, temperature, and the strength of the exchange interaction.

Spin filtering is another critical outcome of proximity-induced magnetism. When a charge current passes through a non-magnetic 2D material coupled to a magnetic layer, the induced spin polarization results in preferential transmission of electrons with a specific spin orientation. This effect has been demonstrated in TMD-based heterostructures, where spin-polarized currents with polarization efficiencies exceeding 30% have been reported. The spin filtering efficiency is influenced by the spin-orbit coupling in the 2D material and the degree of spin polarization induced by the magnetic layer.

Valley polarization, a unique feature of certain 2D materials like MoS2 and WSe2, can also be controlled via proximity coupling. In these materials, the conduction and valence band edges are degenerate at two distinct momentum-space valleys, which can be selectively populated using circularly polarized light. When coupled to a magnetic layer, the valley degeneracy is lifted due to the exchange interaction, leading to valley-polarized states. Experimental studies have shown valley polarization efficiencies of up to 20% in MoS2/CrI3 heterostructures at cryogenic temperatures. The valley polarization is highly sensitive to the magnetic ordering of the adjacent layer and can be modulated by external magnetic fields.

Spin-resolved measurement techniques are essential for characterizing proximity-induced magnetism. Spin-polarized scanning tunneling microscopy (SP-STM) provides atomic-scale resolution of spin textures at the interface, enabling direct visualization of induced magnetic moments. Spin-resolved photoemission spectroscopy (SRPES) measures the energy- and momentum-resolved spin polarization of electronic states, offering insights into the spin-dependent band structure modifications. Magneto-optical Kerr effect (MOKE) microscopy is another powerful tool for mapping local magnetization and hysteresis behavior in 2D heterostructures. These techniques collectively reveal the intricate interplay between spin, charge, and valley degrees of freedom in proximity-coupled systems.

The temperature stability of proximity-induced magnetism remains a challenge, as many effects are quenched at elevated temperatures due to thermal fluctuations. For instance, exchange bias and valley polarization in CrI3-based heterostructures typically diminish above 30 Kelvin, limiting their practical applications. Research efforts are focused on identifying magnetic layers with higher Curie temperatures and optimizing interfacial coupling to enhance thermal stability. Recent studies suggest that iron-based van der Waals magnets may offer improved performance at higher temperatures.

Interfacial disorder and defects can significantly impact the proximity effects by disrupting the coherent exchange interaction. Atomic-level defects, such as vacancies or adsorbates, act as scattering centers for spin-polarized carriers, reducing spin lifetimes and polarization efficiencies. Advanced growth and transfer techniques, including molecular beam epitaxy and dry transfer methods, are being developed to minimize interfacial imperfections and improve reproducibility.

The potential applications of proximity-induced magnetism span spintronics, valleytronics, and quantum computing. Spin-filtering heterostructures can serve as building blocks for low-power spin logic devices, while valley-polarized systems enable valley-based information processing. The integration of these effects with superconducting or topological materials further expands the possibilities for hybrid quantum devices. However, scalability and manufacturability remain critical hurdles, as the precise assembly of van der Waals heterostructures is currently limited to laboratory-scale demonstrations.

Future research directions include the exploration of new magnetic 2D materials with robust magnetic ordering at higher temperatures, as well as the development of dynamic control schemes using electric fields or strain to modulate proximity effects in real time. The combination of artificial intelligence and high-throughput computational screening may accelerate the discovery of optimal material pairings for specific applications. Additionally, advances in spin-resolved characterization techniques will provide deeper insights into the microscopic mechanisms governing proximity-induced magnetism.

In summary, the induction of magnetism in non-magnetic 2D materials via proximity coupling represents a versatile platform for engineering spin-dependent phenomena. The interplay between exchange interactions, spin filtering, and valley polarization offers rich physics and promising technological prospects, provided challenges related to temperature stability and interfacial quality are addressed. Continued progress in this field will rely on interdisciplinary efforts spanning materials synthesis, device engineering, and advanced characterization.