二维双金属铁磁半导体CrMoI_(6)的电子结构与稳定性

Electronic structure and stability of two-dimensional bimetallic ferromagnetic semiconductor CrMoI_(6)

二维磁性半导体由于兼具磁性、半导体性和特殊的二维结构而受到人们的广泛关注,为纳米级自旋电子和光电子器件的研发应用和相关的基础理论研究提供了新的思路和平台.基于第一性原理计算,在对一系列二维双金属碘化物CrTMI_(6)的交换能进行初步筛选的基础上,选出了具有铁磁性的CrMoI_(6)单层结构.进一步计算表明,CrMoI_(6)单层的电子能带结构展示出理想的半导体特性,计算得到的带隙约为1.7 eV,而且还具有很大的磁各向异性能(741.3μeV/TM).通过基于海森伯模型的蒙特卡罗模拟预测这一材料的居里温度达到92 K,约为CrI_(3)单层的2倍.此外,分子动力学和声子谱的计算还证明了其良好的热稳定性和动力学稳定性.这类可以通过合金化方法合成的磁性过渡金属卤化物将进一步拓展二维磁性材料家族及其在自旋电子学器件领域的应用.

Two-dimensional magnetic semiconductors have received extensive attention due to their combination of magnetism,semi-conductivity and special two-dimensional structures,which also provide a new idea and platform for developing the nanometer spintronic and optoelectronic devices and also for conducting the related basic theoretical research.However,in addition to the common problems of two-dimensional magnetic semiconductor materials,such as volume manufacturing and environmental stability,the two-dimensional magnetic semiconductor materials have the unique difficulty,i.e.low Curie temperature,which makes it difficult to maintain ferromagnetic coupling at higher temperature.For example,the Curie temperature of the existing CrI_(3) monolayer is lower than 45 K,while that of the Cr_(2)Ge_(2)Te_(6) double-layer is only 20 K,which is far lower than the room temperature.Therefore,how to improve the Curie temperature of two-dimensional magnetic semiconductor materials through various approaches is one of the important issues that need to be resolved in this field of research.Based on the first-principles calculations,the exchange energies of a series of two-dimensional bimetallic iodides CrTMI_(6)(TM denotes transition metal elements in fourth and fifth rows)constructed from the lattice of CrI_(3) monolayer are preliminarily calculated and screened.Structures are fully relaxed until the force and the energy are converged to 0.01 eV/A and 10^(-6) eV,respectively,and the ferromagnetic CrMoI_(6) monolayer is selected.Further calculations show that the band structure of the CrMoI_(6) monolayer exhibits ideal semiconductor characteristics with a band gap of about 1.7 eV.At the same time,theoretical calculations with considering the spin-orbit coupling show that the CrMoI_(6) monolayer has a considerable magnetic anisotropy(741.3μeV/TM),and its easy axis is perpendicular to the two-dimensional plane.Monte Carlo simulation based on the Heisenberg model predicts that the Curie temperature of CrMoI_(6) monolayer reaches 92 K,which is about twice that of the CrI_(3) monolayer.The molecular dynamics and phonon spectrum calculations also prove that it has both thermal and kinetic stability.In addition,under the condition of applying compressive and tensile strain,its ferromagnetic coupling shows strong stability.This kind of magnetic transition metal halide which can be synthesized by alloying will further expand the family of twodimensional magnetic materials and their applications in the field of spintronic devices.