Long-range magnetoelectricity in type-II multiferroic NiI<sub>2</sub>.

Pan, Weiyi; Chen, Zefeng; Jiang, Tianxing; Wang, Haitao; Wu, Dezhao; Zhu, Weiqin; Xu, Zhiming; Li, Lianchuang et al. · Proc Natl Acad Sci U S A · 2026

basic_science · Level V

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Abstract

Type-II multiferroics, where spin order induces ferroelectricity, exhibit strong magnetoelectric coupling. However, for the typical 2D type-II multiferroic NiI<sub>2</sub>, the underlying magnetoelectric mechanism remains unclear. Here, applying generalized spin-current model, together with first-principles calculations and a tight-binding approach, we build a comprehensive magnetoelectric model for spin-induced polarization. Such model reveals that third-nearest-neighbor spin pairs provide an unexpectedly strong contribution to the electric polarization, which rivals that of the first-nearest neighbors. Adopting such model, both experimental-detectable bound charge induced by spin-induced polarization at the spiral domain boundary, as well as polar vortex lattice induced by magnetic skyrmion lattice under moderate magnetic field, are predicted. Furthermore, by analyzing the orbital-resolved contributions to polarization, our tight-binding model reveals that the long-range magnetoelectric coupling is enabled by the strong <i>e</i><sub><i>g</i></sub>-<i>p</i> hopping of NiI<sub>2</sub>. These findings can guide the identification and design of strongly magnetoelectric multiferroics.