Effect of nitrogen addition on the morphology, magnetic and magnetoresistance properties of electrodeposited Co, Ni and Co–Ni granular thin films onto aluminum substrates

A series of Co, Ni and Co–Ni granular thin films with variable nitrogen content in the range 0–16 at.% N were prepared by electrodeposition onto aluminum substrate. The nitrogen content was varied in order to analyze its influence on the magnetoresistance. The morphology, structure and magnetic properties of electrodeposited Co, Ni and Co–Ni granular thin films were also studied as a function of the nitrogen content. The magnetoresistance (MR) ratio of Co–Ni–N granular films initially increased and then decreased when increasing the nitrogen content. The films exhibit a granular morphology, with rich in nitrogen frontiers between grains and some un-deposited sites on the aluminum substrate, which easily oxidize even during the process of preparation, favoring the spin tunneling transport. We obtained tunneling magnetoresistance (TMR) effect in the Co–Ni–N granular thin films in the range 3–159%; this large effect obtained in Co–Ni–N granular thin films makes them suitable for applications in electronics.

• The effects of the nitrogen content of the physical properties of electrodeposited Co, Ni and Co–Ni films were studied.
• XRD studies showed that the films prepared at lower values of sodium nitrate, exhibited Co hcp structure.
• Granular Co–Ni–N films have unidirectional anisotropy.
• Co–Ni–N granular thin films displayed a tunneling magnetoresistance effect at room temperature.
• The Co–Ni–N electrodeposited granular thin films could be useful to produce low-cost magnetic sensors.