We have calculated the electronic structures of Co2FeAl1-xSix(101) surface using first-principles method based on the density functional theory. Because of the surface effect, the minority spin band gap at the Fermi l...We have calculated the electronic structures of Co2FeAl1-xSix(101) surface using first-principles method based on the density functional theory. Because of the surface effect, the minority spin band gap at the Fermi level disappears at the surface of bulk Co2FeAl1-xSix. However, beneath the surface, the minority spin gap opens at the Fermi level, which indicates that the electronic structures of Co2FeAl1-xSix(101) become close to that of bulk phase. Accordingly, the Co2FeAl1-xSix(101) surface is a composite tri-layer structure that corresponds to the weakening of half-metallic property in Co2FeAl1-xSix films. Even though, the spin polarization of Co2FeAl1-xSix(101) surface is still larger than that of Co2FeAl or Co2FeSi materials, making Co2FeAl1-xSix a promising spintronics material.展开更多
Recently,people are confused with two opposite variations of elastic modulus with decreasing size of nano scale sample:elastic modulus either decreases or increases with decreasing sample size.In this paper,based on i...Recently,people are confused with two opposite variations of elastic modulus with decreasing size of nano scale sample:elastic modulus either decreases or increases with decreasing sample size.In this paper,based on intermolecular potentials and a one dimensional model,we provide a unified understanding of the two opposite size effects.Firstly,we analyzed the microstructural variation near the surface of an fcc nanofilm based on the Lennard-Jones potential.It is found that the atomic lattice near the surface becomes looser in comparison with the bulk,indicating that atoms in the bulk are located at the balance of repulsive forces,and the elastic moduli decrease with the decreasing thickness of the film accordingly.In addition,the decrease in moduli should be attributed to both the looser surface layer and smaller coordination number of surface atoms.Furthermore,it is found that both looser and tighter lattice near the surface can appear for a general pair potential and the governing mechanism should be attributed to the surplus of the nearest force to all other long range interactions in the pair potential.Surprisingly,the surplus can be simply expressed by a sum of the long range interactions and the sum being positive or negative determines the looser or tighter lattice near surface respectively.To justify this concept,we examined ZnO in terms of Buckingham potential with long range Coulomb interactions.It is found that compared to its bulk lattice,the ZnO lattice near the surface becomes tighter,indicating the atoms in the bulk are located at the balance of attractive forces,owing to the long range Coulomb interaction.Correspondingly,the elastic modulus of one-dimensional ZnO chain increases with decreasing size.Finally,a kind of many-body potential for Cu was examined.In this case,the surface layer becomes tighter than the bulk and the modulus increases with deceasing size,owing to the long range repulsive pair interaction,as well as the cohesive many-body interaction caused by the electron redistribution.展开更多
基金supported by the National Natural Science Foundation of China (Nos. 50831002,50971025, 51071022, and 11174031)Beijing Natural Science Foundation (No. 2102032)+1 种基金Program for Changjiang Scholars and Innovative Research Team in University, Beijing Nova Program (No. 2011031)the National Basic Research Program of China (No. 2012CB932702)
文摘We have calculated the electronic structures of Co2FeAl1-xSix(101) surface using first-principles method based on the density functional theory. Because of the surface effect, the minority spin band gap at the Fermi level disappears at the surface of bulk Co2FeAl1-xSix. However, beneath the surface, the minority spin gap opens at the Fermi level, which indicates that the electronic structures of Co2FeAl1-xSix(101) become close to that of bulk phase. Accordingly, the Co2FeAl1-xSix(101) surface is a composite tri-layer structure that corresponds to the weakening of half-metallic property in Co2FeAl1-xSix films. Even though, the spin polarization of Co2FeAl1-xSix(101) surface is still larger than that of Co2FeAl or Co2FeSi materials, making Co2FeAl1-xSix a promising spintronics material.
基金supported by the National Natural Science Foundation of China (Nos10721202,10432050,10772012 and10732090)the CAS innovation program (KJCX2-YW-M04)
文摘Recently,people are confused with two opposite variations of elastic modulus with decreasing size of nano scale sample:elastic modulus either decreases or increases with decreasing sample size.In this paper,based on intermolecular potentials and a one dimensional model,we provide a unified understanding of the two opposite size effects.Firstly,we analyzed the microstructural variation near the surface of an fcc nanofilm based on the Lennard-Jones potential.It is found that the atomic lattice near the surface becomes looser in comparison with the bulk,indicating that atoms in the bulk are located at the balance of repulsive forces,and the elastic moduli decrease with the decreasing thickness of the film accordingly.In addition,the decrease in moduli should be attributed to both the looser surface layer and smaller coordination number of surface atoms.Furthermore,it is found that both looser and tighter lattice near the surface can appear for a general pair potential and the governing mechanism should be attributed to the surplus of the nearest force to all other long range interactions in the pair potential.Surprisingly,the surplus can be simply expressed by a sum of the long range interactions and the sum being positive or negative determines the looser or tighter lattice near surface respectively.To justify this concept,we examined ZnO in terms of Buckingham potential with long range Coulomb interactions.It is found that compared to its bulk lattice,the ZnO lattice near the surface becomes tighter,indicating the atoms in the bulk are located at the balance of attractive forces,owing to the long range Coulomb interaction.Correspondingly,the elastic modulus of one-dimensional ZnO chain increases with decreasing size.Finally,a kind of many-body potential for Cu was examined.In this case,the surface layer becomes tighter than the bulk and the modulus increases with deceasing size,owing to the long range repulsive pair interaction,as well as the cohesive many-body interaction caused by the electron redistribution.
