Microstructures and Magnetic Properties of Electrodeposited Co-Pt Nanowires With Diameters Below 100 nm

We have investigated the effect of the microstructure on the magnetic properties of Co-Pt nanowires (NWs) with diameters of 15, 50, and 80 nm. These Co-Pt NWs were fabricated by using polycarbonate membranes with different pore diameters via direct electrodeposition. A detailed transmission-electron-microscopy analysis revealed that the Co-Pt NWs transform from a polycrystalline to a single-crystalline-like structure along the growth direction of the NWs. The selected-area electron-diffraction investigation of the Co-Pt NWs with 50 nm diameters revealed a fcc-dominant crystal structure, while the 15 and 80 nm NWs were composed of an intermixture of fcc and hcp phases. This investigation allows us to understand the magnetic hysteresis loops of the Co-Pt NW arrays. Furthermore, the magnetic domains of the individual Co-Pt NWs were studied with magnetic force microscope (MFM), and the MFM contrasts for the 50 nm and 80 nm diameter NWs are interpreted as consisting of z-vortices.