Effect of Magnetic Field Annealing Upon Co-Rich Nanowires

The magnetic field (MF) annealing of dc electrodeposited ferromagnetic nanowire arrays of compositions Co₉₄Fe₀₆ , Co₉₁Fe₀₇B₂ was done in the direction of their easy axis of magnetization (in plane) at 265⁰ C under 800 Oe applied magnetic field for 2 h. An induced magnetic anisotropy (MA) and a large increase in saturation magnetization (M_s) were manifested by the changes in hysteresis loops of the nanowire samples before and after the annealing process. The structural changes were investigated using X-ray diffraction and transmission electron microscopy (TEM). The shape of nanowires, the predicted natural texture with c-axis in the plane of membrane (because of high concentration of cobalt) and diffusional pair ordering of unlike atoms along the direction of external applied field were thought to be the causes of induced MA. The reannealing of samples in absence of MF at 400degC and 600degC produced no significant changes in hysteresis loops instead of removing the MA but with evolution of crystalline phase in both the samples. Therefore, the shape of nanowire was concluded to play the major role in persistence of induced MA in nanowire samples after high temperature annealing