Zhu Yan, Gao Yinlu, Jiang Xue, Zhao Jijun
Key Laboratory of Material Modification by Laser, Ion and Electron Beams, Dalian University of Technology, Ministry of Education, Dalian 116024, China.
Phys Chem Chem Phys. 2022 Jul 27;24(29):17615-17622. doi: 10.1039/d2cp01537d.
Long-range ferromagnetic (FM) order in vanadium diselenide (VSe) monolayers (MLs) remains a controversial subject. In this theoretical study, we examined the effect of vacancy defects on the magnetic properties of octahedrally coordinated 1T-VSe MLs using spin-polarized density functional theory (DFT). In total, 45 different kinds of defects with various concentrations were introduced, including two single vacancies (S), 27 double vacancies (D), nine triple vacancies (T), and seven quadruple vacancies (Q). To understand the magnetic properties, S, D-(10), T-(10)(10), and Q-(21)(10)(10) were selected to be analyzed because they had low formation energies and large variations in magnetic moments (). Compared with the perfect VSe ML, the values of the of vanadium (V) decreased from 0.675 to 0.466, 0.183, 0.213, and 0.208 with increasing vacancy concentration. The same trend was also found for the energy differences between FM and antiferromagnetic (AFM) ordering. These results generally indicated weaker FM coupling and a lower Curie temperature in defective VSe. Vacancy-induced lattice distortion, d orbital shifting, electronic occupation, and spin density redistribution were discussed in order to explain the above observations. Our investigation demonstrated a strong dependence of and the magnetic interaction of VSe on the concentration and types of Se vacancies, which would explain the uncertainties encountered in magnetic experiments.
二硒化钒（VSe）单层中的长程铁磁（FM）序仍是一个有争议的话题。在这项理论研究中，我们使用自旋极化密度泛函理论（DFT）研究了空位缺陷对八面体配位的1T-VSe单层磁性能的影响。总共引入了45种不同浓度的缺陷，包括两个单空位（S）、27个双空位（D）、9个三空位（T）和7个四空位（Q）。为了理解磁性能，选择分析S、D-(10)、T-(10)(10)和Q-(21)(10)(10)，因为它们具有低形成能和磁矩（）的大变化。与完美的VSe单层相比，随着空位浓度的增加，钒（V）的磁矩值从0.675降至0.466、0.183、0.213和0.208 。FM和反铁磁（AFM）有序之间的能量差也发现了相同的趋势。这些结果总体上表明缺陷VSe中的FM耦合较弱且居里温度较低。讨论了空位诱导的晶格畸变、d轨道移动、电子占据和自旋密度重新分布，以解释上述观察结果。我们的研究表明VSe的磁矩和磁相互作用强烈依赖于Se空位的浓度和类型，这将解释磁实验中遇到的不确定性。
