Anisotropic magnetic properties of bi-layered structure of ordered Co nanorod array: Micromagnetic simulation and experiments

The angular dependence of magnetic properties were investigated in Co nanowire (NW) arrays with varying length grown by pulse electrochemical route into pore of alumina template. In these investigations, three different NW lengths, 200, 400 and 1000 nm were considered. The structural investigations reveals that shorter NW of length 200 nm have hcp (002) structure, however the existence of both hcp (002) and hcp (100) was observed in longer wire length of 1000 nm, though these phases were well separated in lower and upper segments along the NW axis, respectively. Micromagnetic simulation has been carried out considering the different crystallographic structures as a function of NW length and with the variation of angle between the applied field and the NW axis. Both using experimentally measured magnetization data and micromagnetic simulations, we have inferred that in the nanowire with only hcp (002) structure, the magnetization reversal occurs by coherent rotation, whereas in the case of hcp (100) structure, the reversal phenomena occurs via vortex state and in bilayer structure, the interaction among them leads to a gradual crossover from a coherenet state to vortex along the nanowire axis. Irrespective of the NW length, the angular dependence of H$_c$ was explained qualitatively using the micromagnetic simulation