Supplementary Material

In the Supplementary Material, we present additional data supporting the understanding of the system's magnetic and electronic properties. Figure S1(a)-(c) dissects the individual contributions to the magnetic exchange coupling between distinct V atoms. Figure S2 describes the d-orbital contribution to the AFM magnetic exchange coupling energy between V1 and V2 atoms. Figure S3 shows the relationship between specific heat and temperature was obtained through Monte Carlo simulations conducted on a K-deficient system. Figure S4(a)-(k) displays the spin-resolved band structures and associated spin-splitting energy along a specific momentum space path at kz=0, under varying strain conditions. Figure S5(a)-(k) displays results of the Monte Carlo calculations conducted under different stress conditions, including the relationship between specific heat and temperature for cases considering only FM coupling, only AFM coupling, and all magnetic exchange couplings. The mechanism of K-ion intercalation in magnetic materials and the influence of magnetic anisotropy on the KV2Se2O system are discussed in Supplementary Note 1 and Supplementary Note 2, respectively.