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二维材料磁性的有效调控属于国内外的前沿研究领域. 本文运用基于密度泛函理论的第一性原理方法, 研究了双轴拉伸应变对单层NbSi 2N 4磁性的影响. 声子谱和分子动力学的计算结果表明, 单层NbSi 2N 4结构具有良好的动力学与热力学稳定性. 研究发现单层NbSi 2N 4为无磁金属, 1.5%的双轴拉伸应变可使其转变为铁磁金属. 对单层NbSi 2N 4材料电子结构的分析表明, 拉伸应变诱导的铁磁性具有巡游电子起源: 当不考虑自旋极化时, 单层NbSi 2N 4在费米能级处存在一条半满的能带, 其主要由Nb原子的dz 2轨道贡献, 拉伸应变可使其更局域化, 进而引起斯通纳不稳定性, 导致铁磁性的产生. 此外, 对磁各向异性能的计算表明, 应变可使单层NbSi 2N 4的易磁化轴方向发生垂直-面内-垂直方向的翻转. 基于海森伯模型的蒙特卡罗模拟结果表明, 拉伸应变可显著提高单层NbSi 2N 4的居里温度. 单层NbSi 2N 4的居里温度在2%应变时为18 K, 在6%应变时提高到87.5 K, 比2%应变时提高了386%. 本研究为应变调控二维层状材料的磁性提供了理论参考, 在力学传感器设计和低温磁制冷领域有着潜在的应用前景.The effective control of two-dimensional material magnetism is a frontier research field. In this work, the influences of in-plane biaxial tension strain on the electronic structure, magnetic properties, and Curie temperature of monolayer NbSi 2N 4are investigated by first-principles calculations based on density functional theory and Monte Carlo simulations in the frame of the Heisenberg model. We demonstrate that the monolayer NbSi 2N 4has favorable dynamic and thermal stability through the phonon spectral calculations and ab initio molecular dynamics simulations. It is found that the intrinsic monolayer NbSi 2N 4is a non-magnetic metal, which can be transformed into a ferromagnetic metal by 1.5% tensile strain. The electronic structure analysis of monolayer NbSi 2N 4shows that the ferromagnetism induced by tensile strain is caused by traveling electrons. There is a half-full band at the monolayer NbSi 2N 4Fermi level, which is mainly contributed by the dz 2orbital of the Nb atom. When there is no additional strain, the band is spin-degenerate. Tensile strain can make this band more localized, which leads to Stoner instability, resulting in the ferromagnetic ordering of monolayer NbSi 2N 4traveling electrons. The stability of the ferromagnetic coupling is enhanced with the increase of the strain degree. The calculation results of the magnetic anisotropy energy show that the strain can make the direction of the easy magnetization axis of the monolayer NbSi 2N 4reverse from the vertical direction to the in-plane, and then back to the vertical direction. Furthermore, the strain can significantly increase the Curie temperature of monolayer NbSi 2N 4. The Curie temperature of monolayer NbSi 2N 4is 18 K at 2% strain and 87.5 K at 6% strain, which is 386% higher than that at 2% strain. Strain engineering can effectively control the magnetic ground state and Curie temperature of single-layer NbSi 2N 4. The research results are expected to promote the development of MA 2 Z 4materials in the field of mechanical sensing device design and low-temperature magnetic refrigeration.
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Keywords:
- two dimensional material/
- first-principle/
- magnetism/
- strain
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应变/% 2 3 4 5 6 J/meV –2.430 –5.625 –8.767 –12.109 –16.753 D/meV 1.224 –0.248 0.388 0.596 0.468 
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