Effect of Annealing on the Electrical and Magnetic Properties of Ni-SiO₂ Multilayer Nanocomposites

This study investigates the influence of annealing on the electrical, magnetoresistive, and structural properties of Ni-SiO₂ nanocomposites fabricated by magnetron sputtering. Electrical measurements performed over the frequency range of 4 Hz to 1 MHz and at temperatures between 298 and 333 K revealed that charge transport in the structures is dominated by hopping conduction described by the Mott and Jonscher models. Before annealing, the nanocomposite exhibited behavior characteristic of a system near the percolation threshold, while thermal treatment at 673 K for 30 min significantly reduced conductivity and increased activation energy, indicating reorganization of conductive pathways and increased separation between active centers. Phase angle analysis confirmed the coexistence of resistive and capacitive components, associated with Maxwell-Wagner-Sillars interfacial polarization. Magnetoresistance measurements demonstrated a transition from negative magnetoresistance in the non-annealed sample to positive magnetoresistance after annealing, suggesting a change from spin-dependent scattering to tunneling-dominated transport mechanisms. Electric and magnetic field simulations were carried out, which showed that the magnetic field was uniformly distributed throughout the structure. SEM observations confirmed a granular morphology with increased intergrain separation after annealing, EDS analysis indicated no significant increase in oxidation. The obtained results demonstrate that annealing strongly modifies transport and magnetic properties of Ni-SiO₂ nanocomposites, making them promising materials for magnetoelectronic applications.