Tri-coordinated Au dopant induced out-of-plane ferroelectricity and enhanced ferromagnetism in chromium triiodide

The coexistence of out-of-plane ferroelectricity and ferromagnetism in one single two-dimensional (2D) material is extremely rare but of great importance for both the fundamental understanding of low-dimensional condensed matter physics and the practical applications in next-generation electronic/spintronic devices. Herein, by first-principles calculations, we unveil that Au doping can simultaneously induce switchable electric polarization and enhance the intrinsic ferromagnetism of 2D chromium triiodide (CrI3). The Au dopant occupies one side of the I-6 hollow site and displays a distorted trigonal planar coordination, which is stabilized by the enhanced Au-6s/I-5s and Au-6s/I-5p bonding interactions. Such tri-coordinated Au dopant destroys the lateral centrosymmetry of CrI3, resulting in large out-of-plane electric dipoles that can be switched under a low transition barrier. Moreover, the super-exchange Cr-I-Cr interactions and magnetic anisotropic energy of 2D CrI3 are all strengthened through Au doping. Our results demonstrate the possibility of engineering lateral ferroelectricity through elemental doping to 2D CrI3 and the proposed ferroelectric magnet, Au-doped CrI3, shows promising applications in nanosized electronic and spintronic devices.