Abstract
First-principles density functional theory-based with spin-polarized calculations were used to investigate CoSi/SiO2,CrSi2/SiO2 and FeSi/SiO2 nanowires. The CoSi,CrSi2 and FeSi in bulk are diamagnetic and paramagnetic, but the ferromagnetism in CoSi/SiO2,CrSi2/SiO2 and FeSi/SiO2 nanowires was observed. Due to the distorted /dangling bonds in surface, the electron spin up and spin down in d-orbital from transitional metal atoms become asymmetric. Nanowires grows direction and side direction is determined by high resolution TEM and set side direction linking with amorphous SiO2 to bulid a close nanowire surface structure to simulate by first-principle. The cubic CoSi B20 type (P213) nanowires grow along [211] direction. Magnetization is not only from Co atom in surface, but also caused by internal defect. Set the defect in CoSi to simulate and assign total internal magnetization to the surface Co atom, simulation value is pretty consistent with experimental result. The hexagonal CrSi2 C40 type (P6222) nanowires grows along [0001] direction. The ferromagnetism is caused by distorted/dangling bonds in surface. The simulations are very consistent with measurements by further considering the effects of interfacial roughness and distribution of oxygen around the interface. The cubic FeSi B20 type (P213) nanowires grow along [111] direction. The ferromagnetism is also caused by distorted/dangling bonds in surface. The distance from surface to up and down plane Fe atom is different largely, so the magnetization is different largely, too. To understand the ferromagnetism source in transitional metal silicides can investigate the application in ferromagnetic semiconductor.