Surface Vacancy-Induced Switchable Electric Polarization and Enhanced Ferromagnetism in Monolayer Metal Trihalides

Abstract

Monolayer chromium triiodide (CrI), as the thinnest ferromagnetic material demonstrated in experiment [ Huang et al. Nature 2017 , 546 , 270 ], opens up new opportunities for the application of two-dimensional (2D) materials in spintronic nanodevices. Atom-thick 2D materials with switchable electric polarization are now urgently needed for their rarity and important roles in nanoelectronics. Herein, we unveil that surface I vacancies not only enhance the intrinsic ferromagnetism of monolayer CrI but also induce switchable electric polarization. I vacancies bring about an out-of-plane polarization without breaking the nonmetallic nature of CrI. Meanwhile, the induced polarization can be reversed in a moderate energy barrier, arising from the unique porosity of CrI that contributes to the switch of I vacancies between top and bottom surfaces. Engineering 2D switchable polarization through surface vacancies is also applicable to many other metal trihalides, which opens up a new and general way toward pursuing low-dimensional multifunctional nanodevices.

Nonvolatile Electrical Control and Heterointerface‐Induced Half‐Metallicity of 2D Ferromagnets

“…Sc 2 CO 2 is also a semiconductor with an indirect bandgap of 1.83 eV (Figure b). Our computed bandgaps of both CrI 3 and Sc 2 CO 2 are in good agreement with previous results . Monolayer CrI 3 exhibits distinct electronic properties upon contacting with Sc 2 CO 2 in different polarized states.…”

“…Theoretically predicted in 2015 and experimentally realized by Xu's group in 2017, the single‐layer CrI 3 exhibits the intrinsic ferromagnetism with the magnetic moment of about 3.0 µ B per Cr atom and Curie temperature of 45 K. The discovery of CrI 3 monolayer, the first single‐layer vdW ferromagnets demonstrated in experiments, opened the door for low‐temperature nanospintronics. Due to its potential applications and being an excellent model of 2D vdW ferromagnets for proof‐of‐principle demonstrations, CrI 3 monolayer is among the most studied atomically thin vdW ferromagnets in both theory and experiments …”

Artificial Multiferroics and Enhanced Magnetoelectric Effect in van der Waals Heterostructures

“…[20][21][22] Meanwhile, 2D ferromagnetism has been recently achieved in vdW materials, such as few-layer Cr2Ge2Te3, 23 CrI3, 24 and Fe3GeTe2, 25,26 spurring substantial interests to fabricate ultra-thin magnetic devices and study fundamental properties, such as magnons, spin liquids, and many other quantum states in reduced-dimensional structures. [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44] All these advances pave the way for exploring the existence of 2D multiferroics and magnetoelectronic couplings.…”

Intrinsic Half‐Metallicity in 2D Ternary Chalcogenides with High Critical Temperature and Controllable Magnetization Direction

“…Among the intrinsically magnetic 2D materials reported, it is observed that transition‐metal‐centered octahedral unit is one of the key building blocks . The different electronic occupation configurations of transition metal centers and different interaction between transition metals and coordination atoms lead to various exchange processes and magnetic anisotropic strength, and thus various interesting magnetic behaviors observed recently .…”