Two-dimensional hyperferroelectric metals: A different route to ferromagnetic-ferroelectric multiferroics

Abstract

Recently, two-dimensional (2D) multiferroics have attracted numerous attention due to their fascinating properties and promising applications. Although the ferroelectric (FE)-ferroelastic and ferromagnetic (FM)-ferroelastic multiferroics have been observed/predicted in 2D systems, 2D ferromagnetic-ferroelectric (FM-FE) multiferroics remain to be discovered since FM insulators are very rare. Here, we proposed for the first time the concept of 2D hyperferroelectric metals, with which the insulating prerequisite for the FM-FE multiferroic is no longer required in 2D systems.We validate the concept of 2D hyperferroelectric metals and 2D metallic FM-FE multiferroics by performing first-principle calculations on 2D CrN and CrB2 systems.The 2D buckled monolayer CrN is found to be a hyperferroelectic metal with the FM ground state, i.e., a 2D FM-FE multiferroic. With the global optimization approach, we find the 2D CrB2 system has an antiferromagnetic (AFM)/planar ground state and a FM/FE metastable state, suggesting that it can be used to realize electric field control of magnetism. Our analysis demonstrates that the spin-phonon coupling and metal-

Recent Progress in Two‐Dimensional Ferroelectric Materials

“…[113] Later in 2017, Luo et al proposed the concept of 2D hyperferroelectric metals based on the first-principles calculation of 2D CrN and CrB 2 , revealing that the spin-phonon coupling and metal-metal interactions are two new mechanisms for competing with the depolarization field for stabilizing the OOP polarization and extending the switchable ferroelectric metallic system. [114] Excitingly, after 1 year, the work on the topological semimetal tungsten ditelluride (WTe 2 ) again brought native ferroelectric metal to the public view. [115] Figure 10a shows the bistability in the conductance G of undoped trilayer and bilayer devices, indicating ferroelectric switching.…”

The rise of two‐dimensional van der Waals ferroelectrics

“…In another first‐principles report by Xiang et al, 2D vertical FE was predicted in the buckled phosphorene oxide allotrope which could be used in novel nanoscale multiple‐state memory devices (Luo & Xiang, ). The authors later proposed the existence of 2D vertical FE in buckled CrN (Figure , lower panel) and CrB 2 , where 2D CrN is found to be a 2D hyper‐ferroelectric metal and FM–FE multiferroic, while CrB 2 is a 2D asymmetric multiferroic suitable for realizing electric field control of magnetism (Luo et al, ). They estimated the Curie temperature and polarization of CrN to be 805 K and 6.2 × 10 −12 C/m, respectively.…”

Review on ferroelectric/polar metals

“…xCaxTiO3-  , n-doped BaMnO3 39) , n-dope BiAlO3 39) , n-doped LaFeO3/ YFeO3 39) , NdNiO3 40) , LiOsO3 15,41,42) , LiNbO3 43) , MgReO3 41) , TiGaO3 41) Layered perovskites Ca3Ru2O7 44) ; (Sr,Ca)Ru2O6 30) , Bi5Ti5O17 31) ; Cd2Re2O7 25) , BiPbTi2O6 45) , La2Ti2O7 39) , Sr2Nb2O7 39) , Ca3Ti2O7 39) Antiperovskites Strained ACNi3 (A = Mg, Zn, and Cd) 46) , CeSiPt3 47) LiGaGe-type structure LiGaGe 48) , SrHgPb 49) , SrHgSn 49) , CaHgSn 49) , KMgSb0.2Bi0.8 50) , CaAgBi 51) , LiZnBi 52) , LaAuGe 53) , LaPtSb 53) Two-dimensional materials WTe2 19,20) , MoTe2 54) , CrN 55) , CrB2 55) Others group-V elements (P, As, Sb, Bi) 56) , SnP 57) , BeAu 58)…”