Statistical analysis of the magnetization processes in arrays of electrodeposited ferromagnetic nanowires

We present a statistical analysis of the magnetization processes in arrays of 22-mum-long, 40-nm-wide Co and Ni nanowires, with parallel-to-wire magnetic anisotropy, electrodeposited into porous polycarbonate membranes. This analysis is based on usual magnetization measurements taken with a magnetic field applied parallel to the average wire direction. It is shown that the magnetization curves may contain, in proportions which depend on the magnetic history of the arrays prior to the measurement, two contributions corresponding, respectively, to single-domain wires reversing their magnetization and to wires initially in a multidomain state which are remagnetized to saturation. Despite the extremely large number of wires involved, these two contributions exhibit clearly discernible substructures. These are related to the different and rather weakly distributed characteristic fields that describe the reversal and remagnetization processes: the nucleation and propagation fields. Numerical simulations of the magnetization curves are carried out which allow one to deduce the statistical distributions of these fields. From this modeling of the experimental data, it is shown that two distinct kinds of defects with very different pinning strength are certainly present in the nanowires. Finally, the analysis of the magnetization curves also provides accurate information concerning the distribution of wire orientation in the polycarbonate templates.