Speaker
Description
The discovery of ferromagnetism in monolayer ${\rm CrI_3}$ marked the beginning of a new era in two-dimensional (2D) materials research. However, most 2D ferromagnets exhibit critically low ordering temperatures, limiting their technological applicability [1]. Significant efforts have focused on enhancing the modest Curie temperature ($T_c$) of monolayer ${\rm CrI_3}$ (45 K), with carrier doping emerging as a particularly promising strategy [2]. Theoretical studies suggest that electron or hole doping could elevate $T_c$ to values up to five times higher than the experimental one [3]. Yet, the orbital-resolved mechanisms governing the evolution of superexchange interactions in doped systems remain poorly understood. In this theoretical study, we combine ab initio density functional theory (DFT), spin Hamiltonian modeling, and Wannier function analysis to systematically investigate doping-dependent magnetic interactions in monolayer ${\rm CrI_3}$. By decomposing superexchange pathways into orbital-specific contributions from Cr and I atoms, we correlate shifts in orbital occupancy with changes in magnetic coupling strength. Hole doping suppresses $t_{2g}-t_{2g}$ antiferromagnetic coupling while maintaining ferromagnetic $t_{2g}-e_g$ interaction. In contrast, for electron doping, the enhancement of ferromagnetic $e_g-e_g$ coupling is compensated by a decrease in $t_{2g}-e_g$ interaction. As a result, hole doping proves to be a more effective strategy for increasing $T_c$. Furthermore, we investigate the doping-dependent evolution of spin-orbit coupling (SOC)-driven magnetic interactions. Notably, the Dzyaloshinskii-Moriya interaction (DMI) between the second-nearest neighbors remains unchanged under electron doping but increases dramatically with hole doping, reaching 110% ratio in $D/J_2$ at one hole per unit cell. Most critically, we show that this pronounced DMI enhancement counteracts the rise in $T_c$, leaving it nearly unaltered across a broad doping range. Our work identifies DMI as a key limiting factor for $T_c$ enhancement in carrier-doped ${\rm CrI_3}$, underscoring its essential role in the design of functional 2D magnets.
References
[1] B. Zhang et al., npj Spintronics 2, 6 (2024).
[2] S. Jiang et al., Nature Nanotech 13, 549–553 (2018).
[3] C. K. Singh et al., Phys. Rev. B 103, 214411 (2021).
[4] M. Orozović, B. Šoškić, Ž. Šljivančanin, S. Stavrić, Prospects for increasing the Curie temperature in monolyer CrI3 by carrier doping - manuscript in preparation.
