[论文解读] Effect of O-doping or N-vacancy on the structural, electronic and magnetic properties of MoSi2N4 monolayer

Yan-Tong Bian, Guanghua Liu+3 more|arXiv (Cornell University)|Dec 8, 2020

MXene and MAX Phase Materials被引用 4

一句话总结

本研究通过第一性原理DFT计算，系统研究了氧掺杂（O-N out/in）和氮空位（V-N out/in）对MoSi₂N₄单层材料的结构、电子和磁性性质的影响。结果表明，O-N in和V-N in缺陷可诱导材料由非磁性半导体转变为铁磁金属，且在双轴应变作用下发生磁性相变，凸显其在自旋电子学中的可调潜力。

ABSTRACT

In this letter, the effect of four types of defects (ONout, ONin, VNout and VNin) on the structural, electronic and magnetic properties of MoSi2N4 monolayer were investigated using first-principles calculations. The calculated results reveal that all the four types of defects lead to structural distortions around the O-dopant or N-vacancy, and thereby change the lattice parameter and monolayer height h. Specifically, ONout or ONin increases the lattice parameter, but VNout or VNin is on the contrary. ONout or VNout increases the monolayer height, whereas the height decreases for ONin or VNin. Each of the four types of defects has a fundamental effect on the electronic properties of MoSi2N4 monolayer, which can induce a transition from semiconductor to metal. ONin or VNin plays a vital role in the occurrence of a transition from non-magnetism to ferrimagnetism in MoSi2N4 monolayer. The effect of biaxial strain on the magnetic properties of the two systems with ONin and VNin was subsequently investigated. It is found that the total magnetic moments are less sensitive to biaxial strain whereas the local magnetic moments residing on the Mo atoms are increased for the two systems with ONin and VNin, as strain increases from -3% to 10% and from -9% to 10%, respectively. Furthermore, the magnetic phase transitions between ferrimagnetic and paramagnetic states were found to occur around -4% strain and within the range from -10% to -9% for the two systems with ONin and VNin, respectively. This study may provide a guidance for the application of MoSi2N4 monolayer in the spintronic and magnetic materials.

研究动机与目标

• 系统研究四种不同缺陷（O-N out、O-N in、V-N out、V-N in）对MoSi₂N₄单层材料的结构、电子和磁性性质的影响。
• 确定这些缺陷如何通过结构畸变改变晶格参数和单层厚度。
• 探究缺陷诱导的电子态转变行为，特别是半导体-金属转变。
• 识别非磁性MoSi₂N₄转变为铁磁性的条件，特别是由O-N in和V-N in缺陷引发的情况。
• 研究双轴应变对缺陷工程MoSi₂N₄体系中磁稳定性和相变的影响。

提出的方法

• 采用自旋极化密度泛函理论（DFT），结合广义梯度近似（GGA）和DFT+U修正，实现对电子结构的精确计算。
• 将双轴应变ε定义为ε = (a′ − a′₀)/a′₀ × 100%，其中a′为受应变后的晶格参数，a′₀为原始值，以模拟机械应变效应。
• 对所有缺陷构型进行结构弛豫和总能量最小化，以确定基态几何结构。
• 分析磁矩（总磁矩及Mo原子上的局域磁矩）和自旋极化态密度，评估磁序的稳定性和类型。
• 在-10%至+10%应变范围内开展应变依赖性计算，以探测磁性相变行为。
• 采用固定初始磁性构型和无初始偏置的自旋极化计算，双重验证基态磁性相。

实验结果

研究问题

• RQ1 O-N out、O-N in、V-N out和V-N in缺陷如何影响MoSi₂N₄的晶格参数和单层厚度？
• RQ2 氧掺杂或氮空位是否可在MoSi₂N₄单层中诱导半导体-金属转变？
• RQ3 哪种缺陷构型可触发MoSi₂N₄从非磁性到铁磁性的转变？
• RQ4 双轴应变如何影响O-N in和V-N in缺陷体系中的总磁矩和局域磁矩？
• RQ5 在O-N in和V-N in掺杂的MoSi₂N₄中，磁性相变（铁磁性到顺磁性）在何种应变值下发生？

主要发现

• O-N out和O-N in缺陷使晶格参数a′增大，而V-N out和V-N in缺陷使其减小。
• O-N out和V-N out使单层厚度h增加，而O-N in和V-N in使其减小。
• 所有四种缺陷类型均诱导MoSi₂N₄发生从半导体到金属的转变，从根本上改变了其电子行为。
• 仅O-N in和V-N in缺陷诱导非磁性向铁磁性基态的转变，且通过自旋极化计算确认了稳定的铁磁序。
• 对于O-N in体系，总磁矩对应变变化不敏感，但Mo原子上的局域磁矩在-3%至10%应变范围内增加；在约-4%应变时发生从铁磁性到顺磁性的磁性相变。
• 对于V-N in体系，Mo原子上的局域磁矩在-9%至10%应变范围内增加，且在-10%至-9%应变范围内发生从铁磁性到顺磁性的磁性相变。