First order reversal curves (FORC) diagrams of Co nanowire arrays

Nanowire arrays of Co and Ni have been obtained by current pulse electrodeposition into nanoporous alumina templates. By adjusting the pH of the bath, the microstructure of the Co wires was tailored, resulting in two types of arrays of crystalline Co--hcp, with c-axis nominally parallel (Co (c parallel)), or nominally perpendicular (Co (c perpendicular)) to the wire. First-order reversal curve (FORC) diagrams provide information on average coercivity of the individual nanowire and the factors influencing the field created in the saturated array by the magnetostatic interactions. The dependences of this field on array geometry (wire length and diameter) and saturation magnetization were found to be in excellent agreement with theoretical predictions from a micromagnetic model. For arrays with lower wire diameter, the average coercivity of the individual wires is systematically higher than the coercivity of the array. The most important difference between the two Co series is in the dependence of the FORC diagrams on the wire diameter, with the Co (cl) showing significant pattern changes at large diameters. Two possible sources of those changes are discussed.