Two-Dimensional Ferroics and Multiferroics: Platforms for New Physics and Applications

Abstract

Two-dimensional (2D) ferroics, including ferromagnets, ferroelectrics, ferroelastics, and multiferroics, recently have been theoretically proposed or experimentally revealed. The research has attracted tremendous attention because of the novel physics and promising applications for nanoelectronics, revealing ferroics in the 2D limit. In the present Perspective, we comprehensively review the recent research progress and also the proposed applications of 2D ferromagnetic, ferroelectric, and ferroelastic materials from theoretical and experimental viewpoints. We then introduce the coupling between ferroic orders and highlight the latest research on 2D multiferroic materials. The promising research directions and outlooks are discussed at the end of the Perspective. It is expected that the comprehensive overview of 2D ferroic materials can provide guidelines for researchers in the area and inspire further explorations of new physics and ferroic devices.

Two-dimensional ferroelasticity in van der Waals β’-In2Se3

“…van der Waals (vdW) layered materials have attracted tremendous research efforts to explore emerging physics at reduced dimensionality 1 – 4 . The intrinsically weak interlayer interaction allows each individual layer to behave independently, granting the unique opportunity to preserve bulk properties down to single-layer thickness 5 – 7 .…”

“…Various two-dimensional (2D) functionalities have been discovered in vdW materials 7 , including superconductivity 8 – 10 , ferromagnetism 11 , 12 , ferroelectricity 13 – 17 and antiferroelectricity 18 , 19 , offering a wealth of choices for making ultrathin flexible 2D heterostructure devices 7 , 20 . Among all the ferroic properties, ferroelasticity represents the mechanical equivalent of ferromagnetism and ferroelectricity, with multiple orientation states of spontaneous lattice strain that are switchable under mechanical stimuli 4 , 21 , 22 . It is the origin of the shape-memory effect and superelasticity 23 , 24 , relevant to applications including piezoelectric sensors, mechanical switches, and actuators 4 , 25 – 27 .…”

“…Among all the ferroic properties, ferroelasticity represents the mechanical equivalent of ferromagnetism and ferroelectricity, with multiple orientation states of spontaneous lattice strain that are switchable under mechanical stimuli 4 , 21 , 22 . It is the origin of the shape-memory effect and superelasticity 23 , 24 , relevant to applications including piezoelectric sensors, mechanical switches, and actuators 4 , 25 – 27 . 2D ferroelasticity has also been predicted in monolayer 1T’ transition metal dichalcogenides (TMDs) based on first-principles calculations 28 , 29 , which may couple with other extraordinary properties to realize strain-tunable functionalities and 2D multiferroics 4 .…”

“…It is the origin of the shape-memory effect and superelasticity 23 , 24 , relevant to applications including piezoelectric sensors, mechanical switches, and actuators 4 , 25 – 27 . 2D ferroelasticity has also been predicted in monolayer 1T’ transition metal dichalcogenides (TMDs) based on first-principles calculations 28 , 29 , which may couple with other extraordinary properties to realize strain-tunable functionalities and 2D multiferroics 4 . However, despite several proposed 2D ferroelastic behavior 28 – 31 and one very recent demonstration on micron-thick layered perovskites 32 , 2D ferroelasticity evidenced by the mechanical switch of spontaneous lattice strain in ultrathin vdW materials has not yet been validated experimentally 4 .…”

Two dimensional ferroelectrics: Candidate for controllable physical and chemical applications

“…The structural and thermal stabilities, atomic thickness and reversible polarization are the prerequisites as the 2D ferroelectrics. In this sense, numerous 2D layered materials were theoretically proposed to be ferroelectrics in recent years based on the simulations, the examples include but not limit to hydroxylized graphene, 42 chemical functionalized 2D Group IV, 43,44 graphene analogues (silicene, germanene, and stanene) and Li doped CrI 3 monolayers, and more as summarized in Tang's recent review 45 . However, most of them are barely verified by the measurements or even not experimental synthesized yet.…”