Magnetic and magneto-transport properties of 3D interconnected networks of Ni/Cu and NiCo/Cu multilayered nanowires

Since the discovery of the giant magnetoresistance in multilayered thin films, this effect has been extensively studied by the scientific community in other multilayered nanostructures, such as parallel nanowire networks made of iron, nickel, cobalt or their alloys. The advantage of these structures is the possibility to tune their porosity and pore diameter. Recently, interconnected nanowire arrays have generated interest because they are self-standing and their transport properties can easily be measured. In addition, these systems are more isotropic than parallel nanowire networks and therefore increase the GMR ratio. The objective of this Master's thesis is to investigate the magnetic and magneto-transport properties of 3D interconnected networks of multilayered nanowires. The template-assisted electrodeposition in a single electrolyte bath has been used to grow the multilayered nanowires in track-etched polycarbonate membranes, covered on one side by a metallic cathode. Ni/Cu and NiCo/Cu multilayers with different atomic percentages of Co have been examined. Additionnaly, the pH was fixed to a value of 2 to avoid any magnetocrystalline contribution. Their morphology and composition have been characterised by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The magnetic properties of these multilayered structures have been measured using an alternating gradient magnetometer (AGM) and the magneto-transport properties have been assessed at room temperature and at 12K. By adjusting the electrodeposition conditions, the difficulty to form Ni/Cu multilayers due to phase separation has been highlighted. Thinner magnetic layers have shown to decrease the anisotropy of the system whereas the impact was lower when changing the thickness of the non-magnetic layers. A GMR ratio of 2% has been obtained on a low porosity template at low temperature. Studying the evolution of the addition of Co in the magnetic layers revealed a stabilisation of the Ni and the formation of multilayers. The positive effect of reducing the amount of crossing zones by using lower porosity templates and increasing the Co content on the GMR has been demonstrated. A more isotropic behaviour coupled with higher GMR has been shown when adjusting the size of the multilayers. 44% and 19% of GMR were found at low temperature for higher and lower contents in Co, respectively.