First Principles Calculation Of Two Dimensional Antiferromagnetic Materials Fe₂Ga₂S₅ And AMnBi(A=K?Rb?Cs)

Two dimensional(2D)magnetic materials have attracted extensive attentions in condensed matter physics due to their possible high mobility and phase transition temperature above room temperature.In particular,two dimensional magnetic materials is an ideal platform to design spintronics devises,and host potential applications in information storage devices,pressure sensors and so on.The notable examples of two dimensional magnetic materials found by recent experiments are Cr I₃,Cr₂Ge₂Te₆,Fe₃Ge₂Te₂.In general,the experimental method to obtain two dimensional layers is exfoliated from their bulk with layered structures.Compared with ferromagnetic(FM)materials,antiferromagnetic(AFM)materials have the following advantages:no stray fields,ultrafast dynamics,and the capability for generating large magnetotransport effects.So far,the research on two dimensional magnetic materials presents two challenges.Firstly,the magnetism in the existed experiments are unstable and magnetic transition temperature is relatively weak,which seriously hinders the practical applications.Secondly,the relevant research for the applications have not yet to explore,although the concept of antiferromagnetic spintronics has been proposed for a long time.In order to deal with these challenges,we proposed to search for the new two dimensional magnetic materials with high mobility,phase transition temperature close to or above the room-temperature,and even the appearance of quantum anomalous Hall effect induced by external magnetic field.In this work,based on the First-principle calculations,we have investigated on the physical properties of two types of antiferromagnetic materials,including Fe₂Ga₂S₅and AMn Bi(A=K,Rb,Cs),which mainly includes:1.We theoretically investigate physical properties of two-dimensional Fe₂Ga₂S₅by employing first-principles calculations.It is found that it is an antiferromagnet with zigzag magnetic configuration orienting in the inplane direction,with Néel temperatures around 160 K.The band structure of the ground state shows that it is a semiconductor with the indirect band gap of about 0.9 e V,which could be effectively tuned by the lattice strain.We predict that the carrier transport is highly anisotropic,with the electron mobility up to the order of¹0³cm²V^-1s^-1much higher than that of hole.These fantastic electronic properties make two dimensional Fe₂Ga₂S₅as a promising candidate for the future spintronics.2.Based on first-principle calculations,we investigate the physical properties of the already synthesized AMn Bi(A=K,Rb,Cs)-family materials.We show that these materials are antiferromagnetic,with Néel temperatures above 300 K.They contain AFM ordered Mn layers,while the interlayer coupling changes from ferromagnetic for KMn Bi to AFM for Rb Mn Bi and Cs Mn Bi.We find that these materials are semiconductors with narrow band gap.Owing to the small effective mass,the electron carrier mobility can be very high,reaching up to 10⁵cm²V^-1s^-1for KMn Bi.In contrast,the hole mobility is much suppressed,typically lower by two orders of magnitude.We further study their two-dimensional single layer structures,which are found be AFM with fairly high mobility¹0³cm²V^-1s^-1.Their Néel temperatures can still reach room temperature.Interesting,we find that the magnetic phase transition is also accompanied by a metal-insulator phase transition,with the paramagnetic metal phase possessing a pair of nonsymmorphic-symmetry-protected two dimensional spin-orbit Dirac points.Furthermore,the magnetism can be effectively controlled by the applied strain.As the magnetic ordering is turned into FM,the system can become a quantum anomalous Hall insulator with gapless chiral edge states.