Relation between ferromagnetic layer thickness (NiCu) and properties of NiCu/Cu multilayers

NiCu/Cu multilayers were grown on (110) textured polycrystalline Cu substrates from a single electrolyte containing Ni and Cu ions by electrodeposition. The structural, magnetic and magnetoresistance properties of the NiCu/Cu multilayers were investigated as a function of the ferromagnetic layer thickness. The ferromagnetic NiCu layer thickness of the multilayers was varied from 2 to 10 nm while the nonmagnetic Cu layer thickness was fixed at 1 nm. Energy dispersive X-ray analysis revealed that the Ni content of the films increased and Cu content decreased as the NiCu layer thickness increased. Multilayers have the face centred cubic structure with (220) preferred orientation as their substrates. Also, the highest peak intensity changed from (220) to (111) with increasing NiCu layer thickness. The saturation magnetization, M_s and the coercivity, H_c of the samples was significantly affected by the film compositions that were varied by the ferromagnetic layer thicknesses. The M_s was increased from 36 to 239 emu/cm³ and the H_c increased from 6 to 94 Oe with increasing ferromagnetic layer thickness. The multilayers exhibited either giant magnetoresistance (GMR) or the anisotropic magnetoresistance (AMR) depending on the NiCu layer thickness. The maximum GMR magnitude of 1.5 % was obtained for the films with 4 nm NiCu layer thickness. The MR measurements indicated that the films with the NiCu layer thickness up to ≤4 nm exhibited the GMR effect whereas for the films with 5 nm NiCu thickness the AMR effect appeared, and then the amount of GMR conversion to AMR effect increased as the NiCu layer thickness in the films increased from 5 to 10 nm. Thus, the variation in microstructure of the multilayers and corresponding magnetisation and magnetoresistance changes may arises from the NiCu layer thickness.