First-principles investigation of the emergence of multiferroicity and skyrmions in Cr I 2

The recently discovered van der Waals magnetic semiconductor $\mathrm{Cr}{\mathrm{I}}₂$ shows promise for spintronic applications. Its electronic and magnetic properties are known to be strongly influenced by electronic correlations. In this work, we employ density functional theory calculations where electronic correlations in $\mathrm{Cr}{\mathrm{I}}₂$ are considered within an on-site Coulomb interaction, $U$, with $U$ being determined using the perturbative approach based on the linear-response method. We show that the accuracy of an on-site Coulomb interaction is essential for predicting the noncentrosymmetric orthorhombic ground state of $\mathrm{Cr}{\mathrm{I}}₂$, which allows the existence of ferroelectricity and nonzero Dzyaloshinskii-Moriya interaction (DMI). Our calculation shows that the ground state of bulk $\mathrm{Cr}{\mathrm{I}}₂$ has electric polarization of $0.15\phantom{\rule{0.28em}{0ex}}\textmu{}\mathrm{C}/\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$ pointing along the $z$-axis and the small DMI energy that changes sign with the ferroelectric polarization switching. The DMI and polarization are enhanced to 0.28 meV/formula-unit and $0.63\phantom{\rule{0.28em}{0ex}}\textmu{}\mathrm{C}/\mathrm{c}{\mathrm{m}}^{\ensuremath{-}2}$ when Pt intercalates bilayers of $\mathrm{Cr}{\mathrm{I}}₂$, due to its large spin-orbit-coupling strength and large off-center displacement. Such an enhanced DMI leads to the N\'eel skyrmions, whose handedness is controlled by ferroelectric polarization. Our work contributes to the creation and manipulation of bits in skyrmions-based memory devices.