Frustrated Dipole Order Induces Noncollinear Proper Ferrielectricity in Two Dimensions

Abstract

Within Landau theory, magnetism and polarity are homotopic, displaying a one-to-one correspondence between most physical characteristics. However, despite widely reported noncollinear magnetism, spontaneous noncollinear electric dipole order as ground state is rare. Here a dioxydihalides family is predicted to display noncollinear ferrielectricity, induced by competing ferroelectric and antiferroelectric soft modes. This intrinsic noncollinearity of dipoles generates unique physical properties, such as Z2 × Z2 topological domains, atomic-scale dipole vortices, and negative piezoelectricity.The Landau theory of phase transitions provides an elegant common framework for both magnetic and polar systems. The one-to-one correspondence between physical characteristics, such as ordered phases -ferromagnetic (FM) vs ferroelectric (FE) states, antiferromagnetic (AFM) vs antiferroelectric (AFE) states [see Figs. 1(ab)]-, hysteresis loops, domains, and other properties is well recognized. However, ferrielectric (FiE) systems, with partially compensated collinear dipoles [Figs. 1(cd)], are rare (except in liquid crystals and in a few solids like hybrid improper ferroelectrics [1]) [2], while ferrimagnetic (FiM) materials are fairly common, e.g. Fe 3 O 4 .This incompleteness of dipole orders is even more dramatic with regards to noncollinearity. For magnets, spin noncollinearity has been widely studied [3,4], leading to exotic magnetism-driven polarization (P ) [5], skyrmions [6], and topological anomalous Hall effect [7]. There are several mechanisms to generate these crucial noncollinear spin orders. For example, in geometrically frustrated systems, such as two-dimensional (2D) triangular lattices, the AFM coupling between nearest-neighbor (NN) spins can generate the 120 • order [3]. For other lattices, the exchange frustration, typically involving competition between NN FM (J 1 ) and next-nearest-neighbor (NNN) AFM (J 2 ) couplings, can generate magnetic cycloid or helical arrangements [4].

Iron telluride ladder compounds: Predicting the structural and magnetic properties of BaFe2Te3

“…Moreover, the polar state of BaFe 2 Se 3 is an exotic noncollinear ferrieletric (FiE) phase instead of a plain ferroelectric (FE) one [34,35]. To our best knowledge, noncollinear FiE order was only proposed in a few compounds, such as M O 2 X 2 (M = Mo/W, X=Br/Cl) [36] and strained BiFeO 3 [37]. It is reasonable to assume that finding this exotic 2×2 Block-type magnetic order with quasi one-dimensional ladders defines an effective feasible path to explore FiE materials.…”

Ferroelectricity in strained Hf$_2$CF$_2$ monolayer

“…Such continuous modulation of local dipoles is a result of the energy landscape [Fig. 5(c)], different from the very sharp domain wall predicted in WO 2 Cl 2 which owns the quadruple energy wells [39]. Since the domain wall is close to the model 2 state, it is expected to be metallic, as shown in Fig.…”

Raman Spectra of Bulk and Few-Layer GeSe From First-Principles Calculations

“…Recently, plenty of 2D ferroelectrics have been successfully exfoliated from a bulk structure in experiments, including in-plane ferroelectricity (Chang et al, 2016;Chang et al, 2019;Higashitarumizu et al, 2020), and out-of-plane ferroelectricity (Liu et al, 2016;Zhou et al, 2017;You et al, 2019;Yuan et al, 2019). Beyond experimental works, theoretical studies have predicted that ferroelectricity can survive in 2D materials (Ding et al, 2017;Huang et al, 2018a), in which some even possess noncollinear ferroelectric ordering (Lin et al, 2019;Song et al, 2021). Among these works, group IV chalcogenides (MX, M Sn, Ge; X S, Se) with few-layer have been discovered with intrinsic ferroelectricity and antiferroelectricity in the experiment (Fei et al, 2016), with a fantastic optical selective property as a polarizer (Shen et al, 2018), valley physics (Rodin et al, 2016), a high absorption coefficient as photovoltaic cells (Franzman et al, 2010;Shi and Kioupakis, 2015), robust ferroelectricity as nonvolatile storage (Wang and Qian, 2017) and so on (Yagmurcukardes et al, 2016).…”