Magnetic aftereffect in quasi-1D amorphous ferromagnetic nanocolumns

2.5 nm wide amorphous ferromagnetic nanocolumns were prepared by swift heavy ions irradiation of paramagnetic YCo₂ thin films. The shape anisotropy-induced coercive field H_C is approximately half the anisotropy field H_A. Magnetic aftereffect measurements reveal that the activation volume involved during magnetization reversal is comparable to the particle size. Given the small diameters involved, such a behaviour can be addressed either by Stoner-Wohlfarth rotation with surface perturbation or to the end-surface nucleation of a 1-D domain wall. For the later, an upper bound of the coercive field, estimated by considering a simple planar configuration, yields a reduced H_c/H_A ratio in agreement with the experimental value