Systematicab initiostudy of the magnetic and electronic properties of all3dtransition metal linear and zigzag nanowires

Abstract

The magnetic and electronic properties of both linear and zigzag atomic chains of all $3d$ transition metals have been calculated within density functional theory with the generalized gradient approximation. The underlying atomic structures were determined theoretically. It is found that all the zigzag chains except the nonmagnetic Ni and antiferromagnetic (AF) Fe chains, which form a twisted two-legger ladder, look like a corner-sharing triangle ribbon and have a lower total energy than the corresponding linear chains. All the $3d$ transition metals in both linear and zigzag structures have a stable or metastable ferromagnetic (FM) state. Furthermore, in the V, Cr, Mn, Fe, and Co linear chains and Cr, Mn, Fe, Co, and Ni zigzag chains, a stable or metastable AF state also exists. In the Sc, Ti, Fe, Co, and Ni linear structures, the FM state is the ground state, while in the V, Cr, and Mn linear chains, the AF state is the ground state. The electronic spin polarization at the Fermi level in the FM Sc, V, Mn, Fe, Co, and Ni linear chains is close to 90% or above, suggesting that these nanostructures may have applications in spin-transport devices. Interestingly, the V, Cr, Mn, and Fe linear chains show a giant magnetolattice expansion of up to 54%. In the zigzag structure, the AF state is more stable than the FM state only in the Cr chain. Both the electronic magnetocrystalline anisotropy and magnetic dipolar (shape) anisotropy energies are calculated. It is found that the shape anisotropy energy may be comparable to the electronic one and always prefers the axial magnetization in both the linear and zigzag structures. In the zigzag chains, there is also a pronounced shape anisotropy in the plane perpendicular to the chain axis. Nonetheless, in the FM Ti, Mn, and Co linear chains and AF Cr, Mn, and Fe linear chains, the electronic anisotropy is perpendicular, and it is so large in the FM Ti and Co linear chains as well as in AF Cr, Mn, and Fe linear chains that the easy magnetization axis is perpendicular. In the AF Cr and FM Ni zigzag structures, the easy magnetization direction is also perpendicular to the chain axis, but in the ribbon plane. Remarkably, the axial magnetic anisotropy in the FM Ni linear chain is gigantic, being $\ensuremath{\sim}12\phantom{\rule{0.3em}{0ex}}\mathrm{meV}$/atom, suggesting that Ni nanowires may have applications in ultrahigh density magnetic memories and hard disks. Interestingly, there is a spin-reorientation transition in the FM Fe and Co linear chains when the chains are compressed or elongated. Large orbital magnetic moment is found in the FM Fe, Co, and Ni linear chains. Finally, the band structure and density of states of the nanowires have also been calculated to identify the electronic origin of the magnetocrystalline anisotropy and orbital magnetic moment.