室温二维磁性半金属的结构预测及其电子性质探究

Since the discovery of graphene, the study of two-dimensional (2D) materials has undergone a vigorous development for fifteen years. However, whether magnetism can exist in 2D platforms is a hot topic and widely discussed in the scientific community. Recently, by using mechanical exfoliation method, 2D intrinsic magnetic CrI3 and Cr2Ge2Te6 layers have been successfully realized, indicating a new era for the study of 2D magnetic materials. Nevertheless, the low curie temperature and trivial band dispersions in these 2D layers significantly restrict their application in spintronics. This project aims to discover new 2D magnetic monolayers with high stability, room-temperature magnetism and novel electronic properties by first principles calculations combined with particle swarm optimization. The dynamical and thermal stabilities will be conformed based on density functional perturbation theory and molecular dynamics simulations, respectively. Electronic band dispersions will be calculated by different exchange correlation functionals. By considering the spin–orbit coupling effect, the maximally localized Wannier functions will be constructed to study the edge state and Chern Number. The Curie/Néel temperature (Tc/TN) will be estimated based on Classical Heisenberg model as implemented in Monte Carlo simulations. The strain effect will be applied to manipulate the spin exchange interaction and to control Tc/TN. The mechanism on how to improve Tc/TN in these 2D platforms can be also revealed. This project provides a good guidance for the future synthesis and investigation of room-temperature 2D magnetic half-metals.

自从石墨烯发现至今，二维材料已经经历了十五年的蓬勃发展。然而，磁性能否在二维材料中存在一直是科学界探讨的热点问题。最近，具有內禀铁磁性的二维CrI3和Cr2Ge2Te6通过机械剥离方法相继合成，开创了二维磁性材料研究的新阶段。然而，较低的居里温度以及平庸的能带色散关系限制了其在自旋电子器件领域的发展。本项目拟利用第一性原理计算结合粒子群算法，发现具有高稳定性，室温磁转变温度，新奇电子性质的二维磁性结构。基于密度泛函微扰理论以及分子动力学研究动力学及热力学稳定性；应用不同交换关联泛函，研究能带色散关系; 考虑自旋轨道耦合效应，构造最大局域化瓦尼尔函数，计算边界态以及陈数；基于经典海森堡模型的蒙特卡洛模拟研究居里温度Tc/奈尔温度TN；采用应力改变磁交换相互作用，从而调控磁转变温度，发现提高Tc/TN的内在规律。本课题对于实验上新型室温二维磁性半金属的合成以及性质探究具有一定指导意义。

发现具有室温磁转变温度的新型二维磁性材料是自旋电子学领域的研究热点之一。本项目针对目前已经发现的二维磁性材料居里温度较低、电子性质较为平庸等问题，致力于探索具有高磁转变温度和新奇电子结构的二维铁磁/反铁磁半金属材料。本项目按照任务书内容进行研究，主要完成了以下工作：（1）应用金属锰元素对二维硼基单层进行修饰，预测了MnB6单层结构，通过蒙特卡罗模拟计算发现其磁转变温度为470K，具有高于室温的居里温度。（2）发现了反铁磁奈尔温度高达1050K的MoB3单层，以及铁磁居里温度达到390K的MoB4单层。MoB3呈现出的狄拉克节线特征，使其在电子器件领域具备应用前景。（3）发现了奈尔温度达到360K的MnO反铁磁单层，通过电场的调控可使其发生从反铁磁半导体转变为铁磁金属，这为将来调控具有特定功能化的二维磁性材料提供一种思路。

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