Tuning The Magnetic Properties Of NbS₂,TiTe₂ And Borophene By 3d Transition Metal:A First Principle Study

Recently,by the large progress of the technique to synthesis and preparation two dimension material,we have witness the emerge of the graphene,phosphine and brophene.The electronic devices designed by the unique structure and electronic properties of these materials behave excellent performance,which aroused the interest to study the future application of two dimensional materials in nano-electronics.Driven by the trend of two dimensional material,transition metal diachalcogenides(TMDs)have dawn lots of attention owing to their low dimensional properties and plentiful physical properties,meanwhile the potential application of TMDs on nanoelectronices have also been proposed.As a matter of fact.the huge success of the MoS2 in naonoelectronices and optoelectronics has proved the potential of TMDs in future application in nano-electronics.However,let along the advantage in the application in transitional electronics,the lack of the robust magnetism within the TMDs family has restrict its future application in spintronics.So,find the effective way to introduce magnetism into TMDs is of the important meaning,not only for the electronic industrial interests but also the need to have a better understanding of the interesting properties in TMDs.Up to now,many works have been done to investigate how to effectively introduce magnetism into TMDs.Based on their results,strain,vacancy doping and edge decoration all can introduce magnetism into TMDs.Among these tuning strategies,as the best of our knowledge,the 3d transition metal doping play the most important role.Since the 3d transition metal doping has proved its value in introducing magnetism in TMDs,we are facing two questions,first,what element of the 3d transition metal can effectively introduce ferromagnetic into TMDs.second,what is magnetism when the 3d transition metal introduce magnetism into TMDs?However,to our best knowledge,the direct answers to these two questions are few.To answer these questions,under the framework of the density functional theory(DFT)we have take the following three works.Firstly,we focused on the magnetic and electronic properties when intercalated 3d transition metal into NbS2.Secondly,we study the magnetic properties when partly replace the Ti with Cr in TiTe2.Finally,we investigate magnetic properties of the brophene adsorption 3d transition.The chapter is organized as follows:At the first chapter,we reviewed the history of the low dimensional material and the TMDs.and then,we present the importance of introduce magnetism into TMDs and how to introduce magnetism into TMDs.Finally we present the current understanding of tuning the magnetic properties of TMDs by 3d transition metal,and then we analysis what we can do in this issue.At the second chapter,we introduce the concept of the DFT,the itinerant ferromagnetism theory and the band unfolding technique that used in our calculation.At the third chapter,we investigate the magnetic and electronic properties of the 3d transition metal intercalated 2H-NbS2.The results indicate that by the concentration of 1/4,the V,Cr,Mn,Fe,Co intercalated 2H-NbS2 show up ferromagnetic ground state.And the value of the Stnoer criteria indicate such ferromagnetic ground state originate from the contribution of the itinerant ferromagnetism.Furthermore,we also investigate the band structure of the intercalated 2H-NbS2 using the band unfolding theory.By comparing with the band structure of the 2H-NbS2,we find the changes of the band structure are not corresponding to the expectation of the rigid band model.At the fourth chapter,we discuses the magnetic properties of the 1T-TiTe2 with the Cr substitution of Ti.The results indicate the Cr substitute can introduce ferromagnetic in 1T-TiTe2.Furthermore,we also observe that the stability of the ferromagnetic can be enhanced by the Cr substitution rate.Meanwhile,by study the electronic structure of these system,we believe the ferromagnetic originate from the contribution of the Ti-Te-Cr superexchange and the Cr-Te-Cr superexchange.At the fifth chapter,we investigate the magnetic and electronic properties of the brophene adsorption of 3d transition metal.The results indicate that by the concentration of 1/8,the Ti,V,Cr,Mn,Fe adsorbed bophene show up ferromagnetic ground state.And the results of the corresponding Stoner criteria indicate such ferromagnetic ground state originate from the contribution of the itinerant ferromagnetism.According to our work,the 3d transition metal can introduce magnetism into TMDs with the tuning strategies of intercalation,adsorption,and substitution.And the study of the originate of magnetism in these system show up that the magnetism can contribution from the inerrant electrons and the superexchange mechanism.Our results suggest that the 3d transition metal can introduce the magnetism into TMDs with the carefully selected atom.And the mechanism of introduce magnetism into TMDs may differ depending on the different system.In other TMDs system,we believe the half metal need further study.We believe our studies provided some foundations of introduce robust magnetism into TMDs.and to other low dimensional system our works can be used as reference.By summarize the role of tuning magnetism in such systems,we can find more low dimensional systems with intrinsic magnetism to expend the future application in spintronics.