Recent success in experimental and theoretical works on metal thiophosphates (MTPs) paved the way to add multiple functionalities of complex oxides, such as ferroelectricity, in 2D materials. To realize multiferroicity and magnetoelectric coupling on layered van der Waals materials, incorporating magnetic ions in the ferroelectric framework is desirable. Unfortunately, replacing the metal ion with a magnetic one in MTPs results in antiferroelectricity in which spontaneous macroscopic polarization is absent. Herein, the emergence of a tunable local ferroelectric state in antiferroelectric CuCrP₂S₆ possessing magnetic Cr³⁺ ion is reported. The spontaneous macroscopic polarization is observed, which is switchable by an external poling field through controlling a defect-dipole polarization in the quasi-antipolar state. The observations suggest that the formation of defect dipoles, which is facilitated by an order-disorder-type structural transition, is likely related to a metastable Cu site within the van der Waals gap and therefore is a smoking gun of the existence of a uniaxial quadruple potential well. The interaction between the defect-dipole polarization and dipoles in the antipolar matrix may lead to the emerging local ferroelectricity in antiferroelectric CuCrP₂S₆. The findings suggest a possibility of utilizing the local ferroelectricity of multiferroic MTPs for novel 2D applications.

中文翻译：

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范德华层状反铁电体 CuCrP2S6 中的可调谐铁电体

最近在金属硫代磷酸盐 (MTP) 的实验和理论工作中取得的成功为在二维材料中添加复合氧化物的多种功能（例如铁电性）铺平了道路。为了在层状范德华材料上实现多铁性和磁电耦合，需要在铁电框架中加入磁性离子。不幸的是，在 MTP 中用磁性离子代替金属离子会导致反铁电性，其中不存在自发宏观极化。在此，在具有磁性 Cr ³⁺的反铁电体 CuCrP ₂ S _{6中出现了可调谐的局部铁电态。}离子被报道。观察到自发宏观极化，通过控制准反极性状态下的缺陷偶极极化，可通过外部极化场进行切换。观察结果表明，由有序-无序型结构转变促进的缺陷偶极子的形成可能与范德华间隙内的亚稳态 Cu 位点有关，因此是单轴四极杆存在的确凿证据潜力很好。缺陷-偶极极化与反极性基体中的偶极之间的相互作用可能导致反铁电体CuCrP ₂ S ₆中出现局部铁电性。研究结果表明利用多铁性 MTP 的局部铁电性进行新型二维应用的可能性。