Magnetic properties of electrodeposited CoFeB thin films and nanowire arrays

A pulse electrodeposition method for preparing stress-free CoFeB thin films is described. The method was optimized to produce amorphous films with soft magnetic properties and the best composition was found to be Co94Fe5B1. The optimized conditions were used to obtain arrays of ordered nanowires, using nanoporous alumina membranes as templates. While magnetization measurements demonstrate that the microstructure of the array influences the detailed characteristics of the hysteresis loops, the general pattern of the magnetization curves, characterized by high saturation fields and low squareness, is the same as for crystalline Co arrays obtained in similar conditions. This observation, as well as data obtained from variable temperature measurements, shows that the overall magnetic behavior is determined mainly by the competition of the shape anisotropy and magnetostatic interactions. Whether the wire axis is easy or hard for the array depends upon the array geometry: wire diameter, length and the packing density of the wires. In order to explain these effects, a micromagnetic model was used to calculate the saturation fields for in-plane and out-of-plane magnetized array, as a function of the geometrical parameters. These agree well with the experimental results.