Layered Co/Cu and Ni/Cu Nanowires: Relationship between the Structure and Magnetic Properties

Abstract—

Co/Cu and Ni/Cu nanowires with metal layers of different thicknesses are obtained by matrix synthesis (the galvanic filling of pores in an ion-track membrane). The electrolytes are selected and the modes of electrodeposition are determined. For cobalt nanowires, the layer thicknesses vary in the range from 25 to 400 nm; for nickel nanowires, samples with thin layers from 7 to 15 nm are obtained. Electron-microscopy studies are carried out, which reveal the strict periodicity of the layers. Magnetic-force microscopy performed on a cleaved membrane with nanowires shows their division into domains and the weak interaction of neighboring nanowires. According to the results of magnetometry, the direction of the easy magnetization axis in Co/Cu nanowires depends on the geometry of the magnetic layer. At layer thicknesses greater than the nanowire diameter, the easy magnetization axis is directed along the nanowire axis; as the layer thickness decreases, it becomes perpendicular to the axis. In Ni/Cu samples (7-nm layers), the easy magnetization axis is also located perpendicular to the nanowire axis. An increase in the copper impurity content in these samples leads to a noticeable increase in the coercive force. The giant magnetoresistance effect is found in these samples with a value of about 1%; it is shown to weakly depend on the number of layers and on the copper impurity in the magnetic layer (within the studied limits).