Magnetic field annealing effect and superparamagnetic contributions in one-dimensional CoPt nanostructures

A low cost versatile electrochemical method has been employed to synthesize highly ordered CoPt nanowires (NWs) in anodic aluminum oxide (AAO) templates with average pore diameter of about 100 nm. The structural properties of as deposited NWs have been studied through XRD analysis showing face centered cubic (fcc) as the dominant phase of CoPt NWs. Magnetic properties at room temperature and lower temperature has been investigated with applied field parallel and perpendicular to NWs axis. The easy magnetization axis is aligned perpendicular to NWs owing to the strong magnetostatic interactions among the NWs due to smaller interwire distance (∼15 nm). Furthermore, the as deposited arrays of NWs have been annealed for 2 h at 300 °C in the presence of 1 T magnetic field applied in the direction perpendicular to NWs axis. Magnetic field annealing gives improved structural and magnetic behavior of these one-dimensional (1D) nanostructures resulting improved crystallinity and increased values of coercivity (Hc) and remnant squareness (SQ). Superparamagnetic contributions at lower temperature due to presence of fine nanoparticles in blocking state play important role and leads to enhanced magnetic behavior of CoPt NWs.