Tunneling magnetoresistance in Co-Ni-N/Al granular thin films

In this work, we report on experimental investigation of the influence of nitrogen addition on magnetic and transport properties of Co-Ni granular films with different nitrogen content correlated with the surface morphology. The granular thin films were electrodeposited on aluminium substrate, from the following base solution: 30 g/l CoSO4.7H2O, 50 g/l NiSO4.7H2O, 10 g/l NiCl2.6H2O, 50 g/l Na2SO4.10H2O, 30 g/l H3BO3 and 10 g/l NaCl. Sodium laurylsulphate (C12H25NaO4S) and sodium saccharine (NaC7H4O3NS.2H2O) were used as additives. As a source for nitrogen inclusion in the films by cationic catalysis, sodium nitrate (NaNO3) was introduced in the electrolyte. The concentration of NaNO3 in electrolytic bath was varied with the aim to control the films nitrogen content. Co-Ni-N/Al granular films display tunneling magnetoresistance (2-160%) effect which could be explained mainly by the elastic spin-dependent scattering of conduction electrons at the interface between magnetic grains (constituted of Co-Ni solid solution) and nonmagnetic regions (rich in N inter-granular frontiers and aluminium oxidized substrate).