Table 1. Magnetic properties of SrX (X = S, Se) monolayers substituted with P and As atoms.

System	Supercell	Ground state	ΔE (meV)	Jeff (meV)	TCMFA (K)	TC (K)
SrS	8 × 4	FM	98	49	187	114
	12 × 6	FM	81	41	154	94
SrSe	8 × 4	FM	154	77	286	175
	12 × 6	FM	136	68	252	154

The energy differences ΔE_FM−AFM between the ferromagnetic ground state and the antiferromagnetic metastable state. The effective exchange coupling parameter J_eff. mean field Curie temperature T_C^MFA of the ferromagnetic state are estimated from our DFT total energy calculations. The Curie temperature T_C are estimate by using an empirical relation T_C/T_C^MFA = 0.61.