Two-dimensional ferromagnetism and driven ferroelectricity in van der Waals CuCrP₂S₆

Abstract

Multiferroic materials are potential to be applied in novel magnetoelectric devices, for example, highdensity non-volatile storage. Last decades, research on multiferroic materials was focused on threedimensional (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 fewlayers 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.

Artificial Multiferroics and Enhanced Magnetoelectric Effect in van der Waals Heterostructures

“…[49][50][51] Monolayer Sc2CO2 is predicted to exhibit both in-plane and out-of-plane electric polarizations. 19 Free-standing monolayer Sc2CO2 exhibits an out-of-plane electric polarization of 1.60 C/cm 3 , which is reported to be the largest for a monolayer material.…”

Recent Advances in Quantum Effects of 2D Materials

“…For example, the emergence of 2D magnetic insulators (e.g., CrI 3 ) extends the possibilities of novel device applications, such as spin‐filters and valley manipulation, through vdW heterostructure engineering . Besides, similar emerging 2DLM systems of VSe 2 , VAgP 2 S 6 , CuCrP 2 S 6 , and MnPSe 3 have also aroused much attention due to their outstanding performances in building ferrovalley devices and spin electronics …”

Progress and prospects in low‐dimensional multiferroic materials

“…Their FE order comes from the out‐of‐plane electric dipole moment due to spontaneous displacement of Cu atoms away from the center atomic plane and their ferromagnetism originates from indirect exchange interaction between Cr/V atoms. Moreover, polarized valley degree of freedom has also been predicted in CuCrP 2 S 6 , which can further be switched on and off by an external electric field …”