Ab initio study of ferromagnetism in edged iron nanowires under axial strain

Abstract

We perform first-principles simulations of the magnetic and electronic properties of ferromagnetic (FM) body-centered cubic (bcc) iron nanowires with characteristic sharp edges consisting of (110) and (11̅ 0) surfaces and their response to mechanical strain. An enhanced magnetic moment of 2.83μB is obtained at the edge of the FM nanowire. This enhancement originates from rearrangement of d electrons from the minority-spin t_2g state to the majority-spin t_2g state due to a significant reduction in the number of nearest-neighbor atoms at the edge. The FM phase is the most energetically favorable phase in the nanowire even under relatively high axial strains, whereas the corresponding bulk material exhibits a FM-to-antiferromagnetic transition under the same loading conditions. During tension, a discontinuous change in the magnetic moment is observed at the surface and inside the nanowire due to a bcc–face-centered-cubic structural transition. In contrast, the magnetic moment at the edge is insensitive to applied strain. This is because the majority-spin state is fully occupied at the edge, which restricts the t_2g-e_g electron rearrangement to just the minority-spin state.