Oriented cobalt nanowires prepared by electrodeposition in a porous membrane

Porous alumina membranes with a uniform pore size of 100 nm have been used to prepare arrays of oriented cobalt nanowires by electrodeposition in an applied magnetic field. The hexagonal c-axis lies in the plane of the membrane, perpendicular to the nanowire axis, for material deposited in 0 T or 1.5 T, but in 5 T the c-axis lies at about 70° to the axes of the wires. The degree of field-induced crystallographic orientation is insufficient to overcome the macroscopic demagnetizing field in samples with a large volume fraction of cobalt. The effective demagnetizing factors perpendicular and parallel to the plane of the membrane are Neff⊥=0.7 and Neff∥=0.15, respectively. Pole figures of the vector magnetization measured in a small rotating field of fixed amplitude in a permanent-magnet vector vibrating sample magnetometer are used to deduce torque and hence the effective magnetocrystalline anisotropy.