First-principles Study On Magnetism And Magnetic Anisotropy Of Low-dimension Materials

The magnetism,magnetocrystalline anisotropy and optical properties of monolayer and atomic chain of 4d transition-metal Ru are investigated using the full-potential linearized augmented plane wave method under the generalized gradient approximation.The magnetic moments are 1.039μ_B/atom and 1.130μ_B/atom for monolayer and atomic chain,respectively.And both systems have large magnetocrystalline anisotropy energy(MAE).The magnetic easy axis is along the normal to the monolayer and it is perpendicular to the chain axis in the atomic chain. The optical properties of the two low-dimension Ru systems are investigated by calculating the complex optical conductivity tensor.Both systems exhibit anisotropy in photoconductivity,especially for the atomic chain.The physical origins of MAE and photoconductivity are studied based on the electronic structures.It is found that the changes in crystal field caused by different symmetry breaking in the two low-dimensional Ru systems result in MAE through spin-orbit coupling,while the anisotropy in photoconductivity mainly comes from the crystallographic anisotropy. The MAE of Co₂Si₂ exhibit obviously fluctuation near the Fermi level.By apply doping in the layers of Si and application an electric field two methods to modulate MAE.It's found that the mechanism of manipulating MAE both are changing band filling,leading to the Fermi level moves to the high energy.The study exhibits that there is little changes in the band structure of Co₂Si₂,the band structure is a rigid electronic band structure module.There are obviously changes in the electronic density(E1.Dens.) of the two-layer Co atoms,which provide the MAE of system.The study on Co₂Si_n indicates that there are oscillate of easy magnetization in plan and perpendicularly layer-plan with the change of parity in numbers of Si layer.The study of electronic density indicate the change of parity in numbers of Si layer lead to the electronic density in the inter-space of the two-layer of Co atom behave distinct distributing configuration,while the key factor in causing the fluctuation of MAE in Co₂Si_n.