Spin-Induced Multiferroicity in 2d Transition-Metal-Halides

Two-dimensional multiferroics with large magnetoelectric coupling may open interesting avenues in the context of multifunctional systems. Here, we study a class of spin-chirality-driven van der Waals multiferroic monolayers, such as transition metal halides, by combining first-principles calculations with the generalized spin-current model. The recent reports of multiferroicity in NiI2 layers [Q.Song et al, Nature <b>602</b>, 601 (2022)], obtained via a joint theory-experiments approach down to the single-layer limit, show the potentiality of cross-coupling phenomena in van der Waals magnets. Another example is represented by vanadium dihalide-monolayers, featuring 120-degree frustrated magnetic structures which develop on the underlying triangular lattice and show competing spin-spiral planes spanning the (001) and (100) crystalline planes. The non-collinear spin configurations induce a ferroelectric polarization which is perpendicular to the spin-spiral plane, switched by the spin-chirality change and whose magnitude is not only determined by the strength of the atomic spin-orbit coupling of the halogen anion, but also affected by structural properties.