First-Principles Calculations Of ? Magnetism In Graphene,Silicene And Germanene

The discovery of graphene has opened a new door to the material physicists and chemists in search of more two-dimensional(2D)materials,such as silicene and germanene etc.Experimental and theoretical works have found that graphene has many excellent qualities including high mechanical property and high electrical property.Hence grapheme has become a focus materials in many scientific fields.In addition,graphene can also be applied into spintronics due to its excellent qualities,such as weak intrinsic spin-orbit coupling and long spin coherence time etc.But graphene is nonmagnetic.Thus,generating ferromagnetism especially for long-range ferromagnetism in graphene system is very important to the development of graphene-based spintronics.Up to now,though many methods have been suggested to produce magnetism in graphene.It is still very difficult to realize the ferromagnetism of graphene in a large scale in experiment.Using the first-principles calculations method,in this article,we study the influence of the substrate to the?magnetism of graphene,silicene and germanene systems.It is expected to design a method to introduce large scale ferromagnetism in these two-dimensional materials.This paper include the following two sections:1.Firstly,we studied the stability and magnetism of H atoms adsorbed graphene on the substrates of h-BN and Cu(111),respectively.We designed the different stacking structures that graphene on the substrate of h-BN or Cu(111).We firstly calculated the energies of the two composite systems where a hydrogen atom is respectively adsorbed on the different carbon atom(A or B)of graphene.It is found that the energy difference between two systems is 30 meV in the case of the substrate of h-BN,and the magnetic moments of the two systems are all 1?B.Furthermore,we considered the system including two H atoms adsorbed on grpahene on the different substrates,and calculate the energies of a pair of H atoms adsorbed on the same(AA dimer)and different(AB dimer)sublattices.It is shown that the energy of AA become lower than that of the AB sublattices when the distance between the substrate of h-BN and the graphene is reduced below 1.31?and under the condition of 1%to 5%strains in Graphene/Cu(111)hybrid system.This finding confirms that H atoms would like to adsorbed on the same sublattice of graphene.Therefore,in this case,H atoms can be selectively adsorbed in a large scale,but the magnetism disappears.2.Secondly,we studied the influence of substrate on the?-orbitals magnetism in Graphene/BN(111),Silicene/GaAs(111)and Germanene/GaAs(111)systems.(1)It is found that,for the system of B-terminated Graphene/BN(111),the carbon atom of nonbonding with substrate are magnetic when reduce the distance between graphene and substrate below the 1.463?,and the magnetic moment increases as the distance decreasing.The density of states(DOSs)show the split state appears in the vicinity of E _F and the total DOS is mainly contributed by carbon atom that nonbonding with the substrate.(2)For the Silicene/GaAs(111)system,the?-orbital ferromagnetism can be realized in Silicene/GaAs(111)system in the cases of the Ga-terminated or As-terminated GaAs(111)under the conditions of changing the distance between the silicene and substrate or applying the stress.(3)For the Ga-terminated Germanene/GaAs(111)system,the?-orbital ferromagnetism can also be realized when changing the distance between the germanene and substrate or applying the stress.However,for Ge-terminated Germanene/GaAs(111)system,the?-orbital ferromagnetism can only be realized under2%~5%tensile stress.In summary,the?-orbital ferromagnetism can be realized in Graphene/BN(111),Silicene/GaAs(111)and Germanene/GaAs(111)systems under certain conditions.So this study provides a new route to realize large-scale?magnetism in two-dimensional materials experimentally.