单层铁电SnTe体系内磁性掺杂诱导的多铁性第一性原理研究

Due to the quantum size effect and crystal symmetry breaking, two-dimensional materials show more novel electronic structure and physical properties, such as larger specific surface area, stronger flexibility and ultra-high electron mobility, compared with their three dimensional bulk structure. Various unique physical properties of the two-dimensional materials shine a light on realizing multifunction in advanced devices. Combining the low dimensional properties with the ferroic orders existing in the bulk materials (such as ferroelectric polarization and magnetic ordering) provides more choices for designing and fabricating the new electronic device. And it is also beneficial to investigate the coupling of lattice, spin, charge and orbit under two dimensional limit..Based on the applicant’s recent achievement on the defect engineering (intrinsic defects and doping) to tune the electronic structure and magnetic properties of the low dimension semiconductor materials, this project focuses on the magnetic element doping in ferroelectric material of SnTe with 1-unit-cell thickness. We will reveal the mechanism of stability of coexisting ferroelectricity-ferromagnetism and the coupling relationship between ferroelectric polarization and magnetic ordering at the micro-scale. In addition, the external strain dependence of the multiferroic properties will also be investigated. At last, through this project，we could obtain at least 1-2 kinds of stable structure of two dimensional ferroelectric-ferromagnetic materials, and provide theoretical guidance for designing new two-dimensional ferroelectric-ferromagnetic material.

由于量子尺寸效应和对称性破缺，二维材料与其三维体相结构相比具备更加新奇的电子结构和物理性能，例如更大的比表面积、更强的柔韧性和超高的电子迁移率等。二维材料这些新颖的物性为实现先进电子器件的多元化提供了新思路。将传统材料中被广泛利用的铁性序参量（例如电极化和磁有序）与二维材料相结合不仅可为新型多功能器件的设计和制备提供更广泛的选择，同时也为研究二维极限尺度下晶格、自旋、电荷和轨道的耦合机制提供了新的研究平台。本项目基于申请人近年来在缺陷工程（本征缺陷和掺杂等）调控低维半导体材料电子结构和磁学性质的研究基础上，开展磁性过渡金属掺杂单层SnTe铁电材料长程磁有序行为的调控研究，深入探索单层SnTe材料中铁电-铁磁序参量在微观尺度下的竞争与耦合机制及外加应变作用下体系多铁性能的演化规律等。通过本项目的实施，最终拟探寻1-2种二维铁电-铁磁共存结构，并为设计新型二维铁电-铁磁材料提供系统性理论指导。

得益于量子尺寸效应，在二维材料中，电子被限制在二维的环境中，因此二维材料表现出了独特的物理、电子和化学特性。因此,本项目主要围绕提探究新型二维层状面外铁电材料的厚度依赖相关的铁电行为和设计新型二维多铁性材料：.首先采用缺陷工程，在新型二维铁电SnTe材料中，通过引入磁性过渡元素，打破局域对称性的方式稳定长程磁有序，同时保留其原有的铁电极化特性，进而实现铁电-铁磁的和谐共存。研究表明尽管Mn和Fe掺杂引入的局域畸变削弱了单层铁电SnTe的铁电极化，但是局域对称性破却稳定了掺杂体系Sn1-xMnxTe和Sn1-xFexTe内长程铁磁耦合。显然，缺陷工程调控策略是设计新型二维多铁材料的可行的方法。.其次探究具有新型二维铁电材料CuInP2S6的厚度依赖相关的铁电性能。研究表明块体CuInP2S6同时具有面外和面内铁电极化。随着薄片厚度的减小，CuInP2S6由单斜相向三方相发生结构相变，进而导致面内铁电极化消失。在临界厚度以下的CIPS极化和新结构相共存，可以为层状材料的压电设计和优化提供依据。