Chemically Functionalized Phosphorene: Two-Dimensional Multiferroics with Vertical Polarization and Mobile Magnetism

Abstract

In future nanocircuits based on two-dimensional (2D) materials, the ideal nonvolatile memories (NVMs) would be based on 2D multiferroic materials that can combine both efficient ferroelectric writing and ferromagnetic reading, which remain hitherto unreported. Here we show first-principles evidence that a halogen-intercalated phosphorene bilayer can be multiferroic with most long-sought advantages: its "mobile" magnetism can be controlled by ferroelectric switching upon application of an external electric field, exhibiting either an "on" state with spin-selective and highly p-doped channels, or an "off" state, insulating against both spin and electron transport, which renders efficient electrical writing and magnetic reading. Vertical polarization can be maintained against a depolarizing field, rendering high-density data storage possible. Moreover, all those functions in the halogenated regions can be directly integrated into a 2D phosphorene wafer, similar to n/p channels formed by doping in a silicon wafer. Such formation of multiferroics with vertical polarization robust against a depolarizing field can be attributed to the unique properties of covalently bonded ferroelectrics, distinct from ionic-bonded ferroelectrics, which may be extended to other van der Waals bilayers for the design of NVM in future 2D wafers. Every intercalated adatom can be used to store one bit of data: "0" when binding to the upper layer and "1" when binding to the down layer, giving rise to a possible approach of realizing single atom memory for high-density data storage.

Facile and Versatile Functionalization of Two‐Dimensional Carbon Nitrides by Design: Magnetism/Multiferroicity, Valleytronics, and Photovoltaics

“…So there will be six equivalent anchoring sides that are the vertexes of a hexagon (e.g., K point as shown in Figure 3). As such, NiCl 2 (C 2 N) 6 is 2D multiferroics [31] with a switchable polarization, where the spin distribution will also be altered upon FE switching (see Figure S5 c) The change of in-plane polarization ΔP versus strain for ZnCl 2 (C 2 N) 6 and MgCl 2 (C 2 N) 6 . For example, as displayed in Figure 3a, FE switching of NiCl 2 (C 2 N) 6 can be achieved when the Ni ions are driven from K to K′.…”

Design of Single‐Molecule Multiferroics for Efficient Ultrahigh‐Density Nonvolatile Memories

“…The vertical polarization of TiP/VP in bilayer MoS 2 is greatly enhanced compared with that in bilayer CrI 3 (see Table 2), which are respectively 3.8 and 3.0 × 10 −12 C m −1 in 2D, much higher than previous values predicted in bilayer BN and InSe. [29] The transmission will be nonmagnetic semiconducting when MP molecules bind with the upper layer, but spin-polarized and n-doped when binding with the lower layer. Sci.…”

Progress and prospects in low‐dimensional multiferroic materials

“…Based on first‐principles calculation, Yang et al have shown that halogen‐decorated phosphorene bilayer can be multiferroic with vertical polarization and “mobile” magnetism . The vertical polarization results from the breaking of inversion symmetry by covalent bonds and switchable by the hopping of halogen adatoms between bilayers.…”

“…(a) Design of high‐density two‐dimensional multiferroic tunnel junction array and field‐effect transistor based on halogen‐decorated phosphorene bilayer with vertical polarization and “mobile” magnetism. (Reprinted with permission from Reference . Copyright 2017 American Chemical Society) (b) Side and top views of the structural model for multiferroic CH 2 OCH 3 ‐functionalized germanene layer.…”