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arXiv · 2601.20713

Universality of Type-II Multiferroicity in Monolayer Nickel Dihalides

Aleš Cahlík·Antti Karjasilta·Anshika Mishra·Robert Drost·Mohammad Amini·Javaria Arshad·Büşra Arslan·Peter Liljeroth
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Abstract

The recent discovery of type-II multiferroicity in monolayer NiI${_2}$ indicated a new pathway for intrinsic magnetoelectric coupling in the two-dimensional limit. However, determining whether this phenomenon is a unique anomaly or a general, chemically tunable property of the material class remains unresolved. Here, we demonstrate the universality of type-II multiferroicity in the transition metal dihalides by visualizing the ferroelectric order in monolayer NiBr${_2}$. 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 NiBr${_2}$ is energetically less robust than in its iodide counterpart, consistent with modified superexchange interactions and the reduced spin-orbit coupling. Our results establish the transition metal dihalides as a versatile platform where the stability of magnetoelectric phases can be engineered through chemical substitution.

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Aleš Cahlík, Antti Karjasilta, Anshika Mishra, Robert Drost, Mohammad Amini, Javaria Arshad, Büşra Arslan, Peter Liljeroth. 2026-01-28. Universality of Type-II Multiferroicity in Monolayer Nickel Dihalides. https://doi.org/10.1002/advs.77081

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