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

Abstract

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 MSi 2 N 4 (M = V, Cr) monolayers using crystal field theory, spin−orbital state analyses, and density functional calculations. Our results reveal that the pristine VSi 2 N 4 monolayer exhibits magnetism with a V 4+ 3d 1 S = 1/2 charge-spin state within the triangular prismatic crystal field. However, the strong d orbital hybridization between adjacent V 4+ 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 CrSi 2 N 4 monolayer is nonmagnetic, characterized by the Cr 4+ 3d 2 S = 0 state. Upon substituting nonmagnetic Cr 4+ with Si 4+ , Cr 1/3 Si 8/3 N 4 transforms into an antiferromagnetic insulator with Cr 4+ 3d 2 S = 1 state, featuring a large orbital moment of −1.06 μ B 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.