Extraordinary Magnetic Second Harmonic Generation in Monolayer CrPS4

Abstract A comprehensive study of 2D magnetic ordering mediated second harmonic generation (SHG) is essential for a thorough understanding of 2D magnetic symmetry and its potential nonlinear applications. Here, an extraordinarily large FM‐mediated SHG is demonstrated in CrPS4, which possesses both spatial and time‐reversal symmetry breaking. The spatial inversion symmetry breaking gives rise to an i‐type SHG response. In contrast, the antiferromagnetic (AFM) ordering in the bulk and even‐numbered CrPS4 layers do not produce any magnetism‐mediated c‐type SHG. Remarkably, c‐type SHG emerges in the monolayer and odd‐numbered CrPS4 layers that have an uncancelled FM layer. This is the first observation of FM‐mediated c‐type SHG in 2D vdWs magnets under ED approximation. Furthermore, the magnitude of this FM‐mediated c‐type SHG is on par with that of i‐type SHG resulting from broken crystalline symmetry, marking it as one of the most significant among all known magnetic materials and indicative of a novel generation mechanism. This finding enriches the categories of SHG produced by magnetic ordering and benefits for further understanding of the symmetry and nonlinear optical behavior of 2D magnets.