Characterization of the magnetic properties of multilayer magnetostrictive iron-gallium nanowires

We investigate the magnetic properties of magnetostrictive iron-gallium (Galfenol, [formula omitted], [formula omitted]) nanowires with magnetic force microscopy (MFM) and using micromagnetic modeling software (magpar). Wires with diameters of 150 nm were fabricated in alternating multilayered structures with Fe-Ga and Cu having aspect ratios of [formula omitted] and [formula omitted], respectively, with the goal of minimizing the relative contribution of shape anisotropy to magnetic domain alignment. Micromagnetic simulations of isolated Fe-Ga segments with these dimensions predict that (1) at remanence, two opposing vortex structures will form at the ends of a Fe-Ga segment, with a single domain wall in the middle of the segment and (2) traditional magnetic dipoles will form at the ends of the segment to align with a large (saturation) external magnetic field. MFM results are presented that support these models. At remanence, no contrast is observed in the MFM phase images. Magnetic poles become evident at the ends of the Fe-Ga segments when a magnetic field exceeding [formula omitted] is applied along the length of the nanowire. The direction of the pole alignment is readily flipped by changing the direction of applied field by 180°. Additionally, MFM images show rotation of the magnetic poles in each Fe-Ga segment as they align with fields of [formula omitted] applied at angles of [formula omitted] and [formula omitted] relative to the length of the nanowire. The MFM results support the simulation results and demonstrate that an aspect ratio of [formula omitted] will reduce shape anisotropy effects sufficiently in Fe-Ga nanowire that magnetization can lie off of the nanowire axis.