Probing Type‐II Multiferroicity in Monolayer NiBr ₂

ABSTRACT

The recent discovery of type‐II multiferroicity in monolayer indicated a new pathway for intrinsic magnetoelectric coupling in the two‐dimensional limit. However, whether this phenomenon is a unique feature of or a chemically tunable property of the broader material class has remained unresolved. Here, we demonstrate that type‐II multiferroicity in the nickel dihalides is tunable through halide ligand substitution by visualizing the ferroelectric order in monolayer . Using scanning tunneling microscopy (STM), we resolve atomic‐scale ferroelectric domains and confirm their magnetoelectric origin through reciprocal manipulation experiments: reorienting magnetic order via electric fields and suppressing the electric polarization with external magnetic fields. Furthermore, we find that the multiferroic state in is energetically less robust than in its iodide counterpart, consistent with modified superexchange interactions and the reduced spin‐orbit coupling (SOC). Our results establish the nickel dihalides as a versatile platform where the stability of magnetoelectric phases can be engineered through chemical substitution.