Prediction And Regulation Of Two-dimensional High Magnetocrystalline Anisotropy Materials

People are constantly pursuing lighter,faster,and better storage technologies.Especially since entering the information age,the amount of information that needs to be processed and transmitted has increased dramatically in geometric progression,and people have become more and more demanding on information storage technology.Among various storage methods,magnetic storage technology has been a hot research direction of information storage technology due to its large information storage capacity,long storage time,repeated reading and writing of storage units,long history,mature technology and high cost performance.The most direct way to increase the storage density is to cut back volume of the bit,but the energy required to reverse the magnetization direction will also become lower.When the magnetic storage unit is reduced to a certain size,a superparamagnetic effect will occur,resulting loss of information in storage.The solution to this problem is to design storage materials with high anisotropy.On the other hand,for high magnetocrystalline anisotropy materials,information is difficult to write,so it is important to manually control the magnetocrystalline anisotropy of these materials.Since the successful separation of graphene,two-dimensional van der Waals materials have received extensive attention.Research on these materials reveals new optical and electronic properties.Most of the two-dimensional materials synthesized to date are essentially non-magnetic,and two-dimensional magnetic materials have largely not been developed.Exploring two-dimensional materials with intrinsic ferromagnetism is of great significance to the physics and application of nanoscale spin storage devices.In this paper,the magnetocrystalline anisotropy energy?MAE?of several two-dimensional ferromagnetic materials and their regulation mechanisms are studied by first-principles calculation.?1?Prediction and regulation of magnetocrystalline anisotropy energy of two-dimensional transition metal triiodide.In virtue of first principle calculations based on density functional theory,we have investigated the magnetism of transition metal triiodides XI₃?X=Cr,Mn,Fe,Mo,Tc,Ru,W,Re,Os?monolayers.Our results indicate that CrI₃,TcI₃,RuI₃,ReI₃ and OsI₃ monolayers are ferromagnetic?FM?,while MnI₃,FeI₃,MoI₃ and WI₃ monolayers are antiferromagnetic?AFM?.Interestingly,TcI₃,RuI_3,ReI₃ and OsI₃ monolayers have considerable MAE.Especially,ReI₃ monolayer exhibits the largest MAE in known two-dimensional?2D?van der Waals?vdW?crystals.We further demonstrate that biaxial strain can greatly change MAEs of ReI₃ and OsI₃ monolayers.From the electronic structure analysis,the change in MAE is mainly attributed from the charge transfer between the a and e2states induced by biaxial strain.In addition,we have also found that a tensile strain can lead to a phase transition of ReI₃ monolayer from FM to AFM.?2?Modulation of magnetocrystalline anisotropy in FePt monolayer film by ferroelectric polarization.Reducing the power consumption required for magnetization reversal is an urgent problem for spin storage device.Electric-field control of the MAE using multiferroics is a promising method to solve this problem.Based on density functional theory,we investigated the effects of the ferroelectric polarization on MAE of FePt/PbTiO₃ multiferroic heterostructures.The MAEs of four interfaces including Fe/PbO,Pt/PbO,Fe/TiO,and Pt/TiO of the FePt/PbTiO₃heterostructures with different polarization intensity are calculated.Our results indicated that the interfaces coupling between ferroelectric terminals and ferromagnetic terminals have a very large impact on the MAE of FePt monolayer.Moreover,with the reversal of the polarization orientation of ferroelectric PbTiO₃ film,the MAE of ferromagnetic FePt monolayer has a monotonous but non-linear change.We demonstrated that the reversal of the polarization orientation results in a redistribution of charge density at the interface,thus resulting in a monotonic change in MAE with polarization intensity.