Fig. 1. (Color online) (a, b) Typical spin valve devices made of graphene^{[33, 34]}. (c) The performance of non-local magneto-resistance for CVD graphene spin valve with different channel lengths^[34].

Fig. 2. (Color online) (a, b) Schematics of configurations for 2D spin valve devices, and (c) 2D spin filter tunnel junction (sf-TJ). (d–f) The first spin valve demonstrated using 2D vdW magnetic (Fe-doped TaS₂) materials^[94].

Fig. 3. (Color online) (a) Schematics of CrI₃ sf-TJ^[96]. (b–d) Optical images of several iterations of vdW 2D sf-TJ devices since 2017^{[96, 99, 106]}. Notice that all of them have very small junction area possibly to reduce the number of magnetic domains. (e, f) The magneto-tunneling current and spin-filtered magnetoresistance for a four-layered CrI₃ sf-TJ device^[96].

Fig. 4. (Color online) Optical image of several versions of spin-FETs based on magnetic vdW materials (a) semiconducting CrSiTe₃^[62], (b) semiconducting Cr₂Ge₂Te₆^[110], (c) h-BN encapsulated Cr₂Ge₂Te₆ (red and black dashed lines label the edge of Cr₂Ge₂Te₆ and graphene electrodes, respectively)^[15], and (d) Al₂O₃-assisted exfoliated 4-layered metallic Fe₃GeTe₂^[17], respectively. Scale bars in (c) and (d) are 10 and 100 μm, respectively. (e) Schematic of the tunable Fermi level and simplified spin-polarized band structure of the vdW intrinsic magnetic semiconductor^[15]. (f, g) Gate tuned magnetic hysteresis loops and gate-tuned I–V curves of the few-layered Cr₂Ge₂Te₆ planar FET device^[15]. (h, i) Longitudinal conductivity and Curie temperature of the Fe₃GeTe₂ planar FET as a function of ion liquid gate^[17]. (j) The anomalous Hall curves of the ionic-gated Fe₃GeTe₂ planar FET at different temperatures^[17].

Fig. 5. (Color online) (a, b) Schematic and optical image of a typical Pt/FGT device^[124]. (c) Hall resistivity recorded as a function of current flowing in the 2D vdW heterostructure device. A hysteresis loop can be seen, demonstrating the current-driven magnetic switch of the magnetizations in the FGT layer^[124]. (d) Switching current as a function of externally applied in-plane magnetic fields at different temperatures^[124]. (e) Schematic structure of Pt/FGT device^[125]. (f) Anomalous Hall effect curve of the Pt/FGT device^[125]. (g) Current-induced magnetic switch at different external magnetic fields^[125].

Fig. 6. (Color online) Illustration of different nanostructures for vdW spintronics.

Fig. 7. (Color online) A roadmap for the exfoliated spintronics.

Table 1. A list of typical 2D vdW magnetic materials and their magnetic fingerprints.