CrO_(2)单层:一种兼具高居里温度和半金属特性的二维铁磁体  

CrO_(2) monolayer:a two-dimensional ferromagnet with high Curie temperature and half-metallicity

作　　者：刘冰心 李宗良[1] Liu Bing-Xin;Li Zong-Liang(School of Physics and Electronics,Shandong Normal University,Jinan 250358,China)

机构地区：[1]山东师范大学物理与电子科学学院,济南250358

出　　处：《物理学报》2024年第10期278-286,共9页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11974217)资助的课题。

摘　　要：半金属铁磁体在费米能级附近具有特殊的能带结构,电子极化率可高达100%,在自旋电子学领域备受关注.但是大部分铁磁半金属材料的居里温度远低于室温,这大大限制了二维铁磁半金属材料的实际应用.因此寻找具有高居里温度的半金属铁磁体是一项具有挑战性的工作.本文基于密度泛函理论框架下的第一性原理方法,研究了过渡金属氧化物CrO_(2)单层的晶体结构、电子特性、基态磁性和铁磁相变.形成能计算、声子谱计算和分子动力学模拟表明CrO_(2)具有动力学稳定性和热稳定性,弹性常数计算表明CrO_(2)具有力学稳定性.基于GGA+U和SCAN方法的自旋极化计算表明CrO_(2)单层的磁基态是铁磁态.采用GGA+U方法计算了CrO_(2)的电子态密度和能带结构,CrO_(2)被确认为一种宽带隙的二维铁磁半金属.运用蒙特卡罗模拟方法求解Heisenberg模型,得到CrO_(2)单层是一种居里温度超过400 K的二维本征半金属铁磁体.CrO_(2)单层的高居里温度在二维铁磁材料中并不多见,在半金属材料中更为稀少,这将使它成为制备自旋电子器件和研究自旋量子效应的理想材料.Owing to the complete spin-polarization of electronic states near Fermi energy,half-metallic ferromagnets,especially two-dimensional half-metallic ferromagnets,have garnered significant attention in the field of spintronics.However,the practical applications of these materials are greatly hindered by their low Curie temperatures.Therefore,the exploration of high Curie temperature half-metallic ferromagnets poses a necessary and challenging task.In this study,we predict a two-dimensional transition metal oxide,CrO_(2) monolayer,and employ first-principles calculations to investigate the crystal structure,electronic properties,magnetic ground state,and ferromagnetic phase transition.The calculations of phonon spectrum,elastic constant,and molecular dynamics simulations indicate that CrO_(2) monolayer is dynamically,mechanically,and thermally stable.The convex hull diagram of Cr-O systems shows that the hull energy of the predicted CrO_(2) layer is only 0.18 eV,further confirming the structural stability and large possibility for experimental fabrication.More importantly,the electronic and magnetic properties of CrO_(2) monolayer demonstrate that it is a two-dimensional ferromagnetic half-metal with wide band gap.Five d suborbitals are divided into E_(g) and T_(2g) orbitals because of the crystal field of Cr atom in the center of O tetrahedron,and the spin-polarizations of Eg orbitals make a major contribution to the moment around Cr atom.The ferromagnetic coupling along Cr-O-Cr chain is dominated by the superexchange interaction bridged by O_(2)p orbitals,similar to the typical Mn-O-Mn superexchange model.The magnetic behavior of the Cr spin lattice in a CrO_(2) monolayer is described by a two-dimensional Heisenberg model,in which the exchange coupling anisotropy is ignored and the single ion anisotropy is the main consideration.By solving the Heisenberg model through using the Monte Carlo simulation method,the Curie temperature is determined to be over 400 K.The high Curie temperature ferromagnetism is rare in two

关 键 词：过渡金属氧化物 二维铁磁半金属 居里温度 第一性原理 

分 类 号：O469[理学—凝聚态物理]