Angular first-order reversal curves: an advanced method to extract magnetization reversal mechanisms and quantify magnetostatic interactions

The magnetic properties of ordered hexagonal arrays of Co nanowires (NWs) and nanotubes (NTs) with diameters of 50 nm and interwire/tube distances of 105 nm were studied using first-order reversal curves (FORCs). We report an advanced analysis of angle dependent first-order reversal curves (AFORCs), measured by changing the angle of the applied magnetic field from theta = 0 degrees (parallel to the wire/ tube axis) to 90 degrees (perpendicular). This method allowed us to determine the magnetization reversal mode and to retrieve quantitative information on the magnetostatic interactions between NWs and between NTs. In particular, we found a sharp increase in the coercivity distribution of the NT arrays for theta > 70 degrees, which is attributed to a transition between vortex and transverse reversal modes. Local magnetic interactions are found to prevail in the Co NT arrays, steadily increasing from theta = 0 degrees to 90 degrees. However, in the Co NW arrays the mean magnetic interactions decrease as theta increases, going from ones similar to local interactions to ones smaller than them.