Understanding and tuning exchange coupling which enables the control of the Curie temperature are still one of the major challenges in the field of two-dimensional magnets. In this article, using density functional theory calculations, we investigate the interlayer exchange coupling of two-dimensional $\mathrm{Cr}{\mathrm{X}}_3$ bilayers that have been intercalated with $3d$ transition metals (TMs). Our results show that the interlayer exchange coupling is greatly enhanced in the intercalated bilayers compared to the pristine bilayers due to additional ferromagnetic or antiferromagnetic couplings between the intercalated atoms and the pristine Cr atoms. Electronic structure analysis reveals that the magnitude of the exchange coupling is mainly determined by the transition energy between the electron-doped $e_g$ band of Cr and the narrow $d$-orbital bands of the TM. In addition, ferromagnetic and antiferromagnetic couplings with host Cr atoms are favored for less than half filled and more than half filled $d$ orbitals of the TM, respectively, because of the Pauli exclusion principle and Hund's rule. Our work provides not only a detailed study but also a strategy to tune the interlayer exchange coupling and to raise the Curie temperature of two-dimensional magnets.

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• Magnetic interactions