Stacking-engineered ferroelectricity and multiferroic order in van der Waals magnets

TL;DR

This paper presents a universal method to induce multiferroic properties in 2D van der Waals magnets by manipulating layer stacking, enabling new multifunctional nanoscale devices with coupled magnetic and electric orders.

Contribution

It introduces a systematic approach to engineer multiferroics in 2D materials through stacking modifications, demonstrated with first-principles calculations on bilayer NiI$_2$.

Findings

Bilayer NiI$_2$ becomes ferroelectric when layers are rotated by 180°.

Interlayer charge transfer induces a novel multiferroic order.

Stacking control can systematically discover new 2D multiferroics.

Abstract

Two-dimensional (2D) materials that exhibit spontaneous magnetization, polarization or strain (referred to as ferroics) have the potential to revolutionize nanotechnology by enhancing the multifunctionality of nanoscale devices. However, multiferroic order is difficult to achieve, requiring complicated coupling between electron and spin degrees of freedom. We propose a universal method to engineer multiferroics from van der Waals magnets by taking advantage of the fact that changing the stacking between 2D layers can break inversion symmetry, resulting in ferroelectricity and possibly magnetoelectric coupling. We illustrate this concept using first-principles calculations in bilayer NiI$_2$, which can be made ferroelectric upon rotating two adjacent layers by $180^{\circ}$ with respect to the bulk stacking. Furthermore, we discover a novel multiferroic order induced by interlayer charge transfer which couples the interlayer spin order and electronic polarization. Our approach is not only general but also systematic, and can enable the discovery of a wide variety of 2D multiferroics.