Phonons Regulate Covalency: A New Way to Modulate Magnetism and Curie Temperature of CrI 3

Abstract

Recently, diverse strategies have been exploited to engineer the magnetism of two-dimensional (2D) magnets to widen the application in spintronics. Here, we demonstrate the manipulating of optical phonons on the magnetism and Curie temperature (T C ) of ferromagnetic CrI 3 . The first-principles calculations reveal the anisotropy governed by dipole-dipole coupling exhibits negligible variations under 14 optical phonons, while E 4 g (~18.65%) and A 1 1g (~8.75%) modes can increase the magneto-crystalline anisotropic parameter (K ij ) remarkably. Based on the mean-field theory, we theoretically predict the Curie temperature of CrI 3 monolayer both in the absence and presence of phonon vibrations. Intriguingly, despite E 4 g and A 1 1g mode increase K ij , they decrease T C by 3.76% and 16.10%, respectively. Conversely, E 3 u and A 2 2g modes enhance T C by 6.63% and 4.77%. The underlying mechanism is that E 4 g and A 1 1g weakens the covalency and super-exchange coupling between Cr and I atoms,whereas the E 3 u and A 2 2g modes strengthen them. Our work offers valuable theoretical insights for the applications of 2D magnetic materials in spintronics.