Magnetic Properties of Cobalt Nanostructures Grown Using Porous Anodic Alumina Membrane

Abstract

In this report, the magnetic nanostructure of Co were grown through the nanopores of Anodic aluminum oxide (AAO) template using both electrochemical and physical vapor deposition (PVD) techniques. Detailed investigations on the fabrication of highly ordered nanoporous AAO template in different electrolyte baths were presented. Ordered domain structure with pore diameter of 40±5 nm was achieved in an oxalic acid electrolyte bath at a temperature of 10 ºC and potential of 40 V. Whereas, in H2SO4 electrolyte bath, the optimized pore diameter was obtained as 22±4 nm while anodizing at a temperature around 3 ºC and at a potential of 25 V. As grown membranes were further processed to vary pore diameters without modifying the interpore separation from 40 to 100±10 nm, and 22 to 45±4 nm through a wet chemical route. Structural investigations revealed that Co nanowires have different crystallographic texture while growing them in different conditions: such as pore diameter of the template, the length of the nanowire, pH of the electrolyte, and electrodeposition modes. These changes in crystallographic structure in Co nanowire were reflected while studied their magnetic properties. Both of these structural and magnetic properties were then correlated with a micromagnetic simulation using OOMMF package and detailed understanding of magnetization reversal processes were presented. These studies were further extended by reducing the aspect ratio between the length to wire diameter less than unity and entered into a nanodot array regime trough PVD techniques using attached ultrathin AAO membrane. The magnetic properties of fabricated both soft and hard magnetic nanodot arrays were studied and the experimental results were presented.