Moiré Skyrmions in Twisted CrX₃ (X = I, Br, and Cl) Bilayers: Part (I) Ab Initio Calculations

We present a comprehensive theory of the magnetic phases in twisted bilayer chromium trihalides through first-principles calculations and atomistic simulations [1]. In this talk, the first-principles simulations will be described. Our calculations permit to build an effective spin model for the bilayers with the isotropic and anisotropic Cr-Cr exchange couplings, the single ion anisotropy, and the interlayer exchange coupling. The intralayer Heisenberg exchange coupling is found to be ferromagnetic and with a value that decreases from I to Cl, as expected. The correct (experimental) magnetic anisotropy (out-of-plane for CrI₃ and CrBr₃ and in-plane for CrCl₃) is also reproduced. More importantly, we find that the stacking-dependent interlayer exchange leads to an effective moiré field that is mostly ferromagnetic with antiferromagnetic patches in all three materials. As such, the competing stacking-dependent interlayer interactions can give rise to novel magnetic states upon twisting.

[1] Muhammad Akram, Harrison LaBollita, Dibyendu Dey, Jesse Kapeghian, Onur Erten, and Antia S. Botana Nano Letters 2021 21 (15), 6633-6639