Multiferroic materials have attracted intense interest due to their remarkable static (Matsukura et al., Nature Nanotechnol. 10(3):209–220, 2015; Kurumaji et al., Phys. Rev. B Condensed Matter Mater. Phys. 87(1):1–9, 2013; Tokura et al., Rep. Progress Phys. 77(7), 2014) and dynamic magnetoelectric properties (Pimenov et al., Nature Phys. 2(2):97–100, 2006; Rovillain et al., Phys. Rev. B Condensed Matter Mater. Phys. 81(5):1–5, 2010; Kibayashi et al., Nature Commun. 5:1–7, 2014). Of particular significance are type-II multiferroics, in which inversion-symmetry-breaking magnetic order intrinsically induces ferroelectric polarization via mechanisms such as the spin-current effect and the inverse Dzyaloshinskii-Moriya interaction (Tokura et al., Rep. Progress Phys. 77(7), 2014; Khomskii, Transition Metal Compounds. Cambridge University Press, Cambridge, 2014). This intrinsic coupling between magnetic and electric order parameters leads to record-high magnetoelectric responses (Tokura et al., Rep. Progress Phys. 77(7), 2014; Spaldin and Ramesh, Nature Mater. 18(3):203–212, 2019). Despite ongoing efforts, realizing such phenomena in two-dimensional (2D) materials has remained elusive, yet is critical for advancing nanoscale magnetoelectric devices (Matsukura et al., Nature Nanotechnol. 10(3):209–220, 2015; Huang et al., Nature Nanotechnol. 13(7):544–548, 2018: Jiang et al., Nature Nanotechnol. 13(7):549–553, 2018). In this chapter, we report the discovery of type-II multiferroicity in monolayer NiI \(_2\) , a transition metal-based van der Waals material. This multiferroic phase arises from a proper-screw spin helix with defined handedness, which couples to the electronic system to generate a chirality-controlled electric polarization. Using circular dichroic Raman spectroscopy, we directly probe both the magnetochiral ground state and its associated electromagnon excitations, revealing the presence of dynamic magnetoelectric coupling. Complementary birefringence and second-harmonic generation measurements confirm a highly anisotropic polar electronic state that breaks both inversion symmetry and threefold rotational symmetry. Temperature- and thickness-dependent optical signatures show that this chiral, polar magnetic order persists down to the monolayer limit. Together, these findings identify NiI \(_2\) as the first atomically thin type-II multiferroic and position transition metal dihalides as a promising platform for exploring multiferroicity, chiral magnetism, and ferroelectricity in the 2D limit.

Discovery of Monolayer van der Waals Multiferroic

章节
发表日期：

2025年

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Batyr Ilyas

摘要

Multiferroic materials have attracted intense interest due to their remarkable static (Matsukura et al., Nature Nanotechnol. 10(3):209–220, 2015; Kurumaji et al., Phys. Rev. B Condensed Matter Mater. Phys. 87(1):1–9, 2013; Tokura et al., Rep. Progress Phys. 77(7), 2014) and dynamic magnetoelectric properties (Pimenov et al., Nature Phys. 2(2):97–100, 2006; Rovillain et al., Phys. Rev. B Condensed Matter Mater. Phys. 81(5):1–5, 2010; Kibayashi et al., Nature Commun. 5:1–7, 2014). Of particular significance are type-II multiferroics, in which inversion-symmetry-breaking magnetic order intrinsically induces ferroelectric polarization via mechanisms such as the spin-current effect and the inverse Dzyaloshinskii-Moriya interaction (Tokura et al., Rep. Progress Phys. 77(7), 2014; Khomskii, Transition Metal Compounds. Cambridge University Press, Cambridge, 2014). This intrinsic coupling between magnetic and electric order parameters leads to record-high magnetoelectric responses (Tokura et al., Rep. Progress Phys. 77(7), 2014; Spaldin and Ramesh, Nature Mater. 18(3):203–212, 2019). Despite ongoing efforts, realizing such phenomena in two-dimensional (2D) materials has remained elusive, yet is critical for advancing nanoscale magnetoelectric devices (Matsukura et al., Nature Nanotechnol. 10(3):209–220, 2015; Huang et al., Nature Nanotechnol. 13(7):544–548, 2018: Jiang et al., Nature Nanotechnol. 13(7):549–553, 2018). In this chapter, we report the discovery of type-II multiferroicity in monolayer NiI \(_2\) , a transition metal-based van der Waals material. This multiferroic phase arises from a proper-screw spin helix with defined handedness, which couples to the electronic system to generate a chirality-controlled electric polarization. Using circular dichroic Raman spectroscopy, we directly probe both the magnetochiral ground state and its associated electromagnon excitations, revealing the presence of dynamic magnetoelectric coupling. Complementary birefringence and second-harmonic generation measurements confirm a highly anisotropic polar electronic state that breaks both inversion symmetry and threefold rotational symmetry. Temperature- and thickness-dependent optical signatures show that this chiral, polar magnetic order persists down to the monolayer limit. Together, these findings identify NiI \(_2\) as the first atomically thin type-II multiferroic and position transition metal dihalides as a promising platform for exploring multiferroicity, chiral magnetism, and ferroelectricity in the 2D limit.