In this study, researchers found that the existence of crystal defects in chemically synthesized Ni_1-xCo_xPS₃ nanosheets, i.e., sulfur vacancies (S_v), could suppress the strong intralayer antiferromagnetic exchange interaction (J₃) in NiPS₃, and the Co substitution decreases the formation energy of S_v during the synthesis process.

Besides, they found that the conversion synthesis process for the Ni_1-xCo_xPS₃ nanosheets are necessary to promote the formation of S_v. S_v do not seem to exist in sufficient quantity in chemical vapor transport grown single crystal. The presence of S_v in Ni_1-xCo_xPS₃ nanosheets led to the suppression of long-range AFM correlations while other competing ferromagnetic exchange interactions dominate at low temperatures, creating a magnetically frustrated system.

As a consequence, the magnetic field required to tune this defect mediated ferromagnetic state (< 300 oersted) is much lower than the value needed to tune a typical vdW antiferromagnet (> several thousand oersted), which made these nanosheets more appealing for spintronic applications.

Theoretically, in correlated NiPS₃, the half-filled Ni e_g orbitals coupled with half-filled S 3p orbitals, which mediates the electron hooping between neighboring Ni sites through superexchange interaction. Owing to the negative charge transfer energy, the S ligand transfers one electron to the half-filled e_g Ni 3d orbital to form a d⁹L ground state, namely negative charge transfer (NCT) state. NCT state also dominates between antiferromagnetically aligned neighboring Ni atoms. In this case, the presence of S_v could affect the electronic correlation and then tune the magnetic ordering in correlated NiPS₃.

These findings provide a less explored route for controlling competing correlated states and magnetic ordering by defect engineering in 2D vdW magnets.