低维有机多铁材料的磁电耦合机理及自旋输运特性研究

Multiferroics are new functional materials that exhibit more than one primary ferroic orders simultaneously, such as ferroelectricity, ferromagnetism, and ferroelasticity. The coupling between ferroelectricity and ferromagnetism, termed the magnetoelectric effect, has attracted great attentions in recent years, due to its huge potentional application in novel devices, such as sensors, harvesters, memeories, and so on. Based on the organic multiferroics synthesized experimentally, we propose theoretical quantum models to investigate their magnetic properties, ferroelectric properties, quantum phase transitions, and thermodynamic properties, by means of Green's function theory. Meanwhile, the microscopic mechanism of megnetoelectric coupling, as well as the effect of electronic field(magnetic field) on magnetization(polarization) will be investigated. In addition, we will design molecular devices by using organic multiferroics. With the combination of non-equilibrium Green's function approach and density functional theory, it is necessary to consider the electron and spin transport properties, the surface effect, and interface effect, which will provide theoretical guide for the design and assembly of organic molecular devices, and promote the development of organic spintronics.

多铁性材料是一种具有多种铁性（如铁电性、铁磁性和铁弹性）的新型功能材料，由于铁电、铁磁两种有序之间的耦合作用(磁电效应)使其在诸如传感器、俘能器和存储器等新型多功能器件上有巨大的应用前景,引起人们的广泛关注。本项目基于实验上合成的有机多铁材料，抽象出量子理论模型，采用量子统计的格林函数理论方法对其磁性、铁电性、量子相变、热力学性质进行研究，分析磁电耦合作用的微观机理，探讨其电场调控磁化强度，以及磁场调控电极化强度的调控手段。并且利用有机多铁材料设计分子元器件，采用非平衡态格林函数与密度泛函理论相结合的方法对器件的电子和自旋输运性质、界面和表面效应等进行研究，为有机多铁分子元器件的设计和组装提供理论指导，促进有机自旋电子学的发展。

我们对有机物多铁材料的磁性和电性进行了研究，尤其是其中含有DM作用的多铁模型，发现了其磁化平台，电极化强度以及相变温度等性质表现出对均匀的DM相互作用和交错DM相互作用的一系列不同响应。并利用非平衡态的格林函数（NEGF）结合密度泛函（DFT）理论，研究了一系列一维有机金属分子线及团簇的负微分电阻（NDR）等效应；多铁材料异质结的磁电效应产生原因和铁电性出现的临界厚度等等。此外我们还以2D铁电材料为基础，设计了一系列新的异质结构：2D超高开关率的铁电场效应晶体管；狄拉克费米子可在电子空穴间切换的拓扑晶体管；拥有超高电阻的铁电结；可以通过电场调控自旋的多铁结。这些体系结合了纳米电子学半导体的超高迁移率还有非易失性存储的高速读写能力，可以为以后研究和制作新型分子器件提供指导和借鉴。