The development of room-temperature magnetic semiconductors is critical for advancing spintronic technologies, yet van der Waals magnets like ${\mathrm{CrI}}_3$ exhibit intrinsically low Curie temperatures ($T{}_{\mathrm{C}} \sim 45$ K). This study employs first-principles calculations to demonstrate that atom intercalation, particularly lithium (Li), dramatically enhances magnetic-exchange couplings in ${\mathrm{CrI}}_3$, achieving near-room-temperature ferromagnetism with a predicted $T{}_{\mathrm{C}}$ of 286 K, aligning with experimental reports of 420 K. The underlying mechanism involves synergistic superexchange and double-exchange interactions: intercalation reduces the $|E_p-E_d|$ energy difference between iodine p-orbitals and chromium $d$ orbitals, strengthening superexchange pathways, while charge transfer induces valence mixing (e.g., ${\mathrm{Cr}}^{3+}$ to ${\mathrm{Cr}}^{2+}$, as confirmed by experimental x-ray photoelectron spectrometry data), promoting double exchange. Theoretical predictions extend to other intercalants including Cu and Na, with ${\mathrm{Cu}}_{0.25}{\mathrm{CrI}}_3$ and ${\mathrm{Na}}_{0.25}{\mathrm{CrI}}_3$ exhibiting $T{}_{\mathrm{C}}$ of 267 K and 247 K, respectively, establishing a versatile strategy for designing high-$T{}_{\mathrm{C}}$ magnetic semiconductors. This work bridges theoretical insights and experimental validation, offering a transferable framework for intercalation-driven material design and accelerating practical spintronic device realization.

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• First-principles calculations
• Magnetic interactions
• Magnetism