Exploration of the Two-Dimensional Ising Magnetic Materials in the Triangular Prismatic Crystal Field

Magnetic anisotropy is essential for stabilizing two-dimensional (2D) magnetism, which has significant applications in spintronics and the advancement of fundamental physics. In this work, we examine the electronic structure and magnetic properties of triangular prismatic MSi2N4 (M = V, Cr) monolayers using crystal field theory, spin–orbital state analyses, and density functional calculations. Our results reveal that the pristine VSi2N4 monolayer exhibits magnetism with a V4+ 3d1 S = 1/2 charge-spin state within the triangular prismatic crystal field. However, the strong d orbital hybridization between adjacent V4+ ions disrupts the d orbital splitting in this crystal field, resulting in a relatively small in-plane magnetic anisotropy of approximately 2 μeV per V atom. In contrast, the pristine CrSi2N4 monolayer is nonmagnetic, characterized by the Cr4+ 3d2 S = 0 state. Upon substituting nonmagnetic Cr4+ with Si4+, Cr1/3Si8/3 N4 transforms into an antiferromagnetic insulator with Cr4+ 3d2 S = 1 state, featuring a large orbital moment of −1.06 μB oriented along the z-axis and huge perpendicular magnetic anisotropy of 18.63 meV per Cr atom. These findings highlight the potential for further exploration of 2D Ising magnetic materials within a unique triangular prismatic crystal field.