Discovery of Two-Dimensional Multiferroicity in van der Waals CuCrP2S6 Layers

TL;DR

This paper predicts and experimentally confirms multiferroic properties in 2D CuCrP2S6 layers, including ferromagnetism and ferroelectricity, offering new opportunities for nanoscale magnetoelectric devices.

Contribution

It introduces the first prediction and experimental validation of multiferroicity in 2D CuCrP2S6, highlighting its potential for device applications.

Findings

Room-temperature out-of-plane ferroelectricity observed in few-layer CuCrP2S6

2D ferromagnetism inferred from magnetic hysteresis at 10 K

Coupled spins, electric dipoles, and valley degrees of freedom

Abstract

Multiferroic materials are potential to be applied in novel magnetoelectric devices, for example, high-density non-volatile storage. Last decades, research on multiferroic materials was focused on three-dimensional (3D) materials. However, 3D materials suffer from the dangling bonds and quantum tunneling in the nano-scale thin films. Two-dimensional (2D) materials might provide an elegant solution to these problems, and thus are highly on demand. Using first-principles calculations, we predict ferromagnetism and driven ferroelectricity in the monolayer and even a few-layers of CuCrP2S6. Although the total energy of the ferroelectric phase of monolayer is higher than that of the antiferroelectric phase, the ferroelectric phases can be realized by applying a large electric field. Besides the degrees of freedoms in the common multiferroic materials, the valley degree of freedom is also polarized according to our calculations. The spins, electric dipoles and valleys are coupled with each other as shown in the computational results. In experiment, we observe the out-of-plane ferroelectricity in a few-layer CuCrP2S6 (approximately 13 nm thick) at room temperature. 2D ferromagnetism of few-layers is inferred from magnetic hysteresis loops of the massively stacked nanosheets at 10 K. The experimental observations support our calculation very well. Our findings may provide a series of 2D materials for further device applications.