Chemical stability and magnetic behavior of supported Ni nanoparticles on TiO₂ nanovoids substrates: Role of surface oxidation and nanoparticle morphology

This study presents the synthesis and characterization of nickel nanoparticles (Ni-NPs) supported on TiO₂ nanovoids (TiO₂-NVs) substrates. The fabrication process involves titanium anodization, mechanical exfoliation, and a cathodic activation treatment that induces Ti³⁺ species generation, enhancing surface conductivity and promoting homogeneous nanoparticle nucleation. Ni-NPs were subsequently deposited by galvanostatic pulsed electrodeposition (PED). FE-SEM and AFM analyses reveal nanoparticles with diameters between 18 and 40 nm confined within the nanovoids. High-resolution XPS reveals the coexistence of metallic and oxidized Ni species and are consistent with the coexistence of oxidized surface species and metallic Ni contributions. The magnetic response is investigated through nano-MOKE measurements and micromagnetic simulations using OOMMF. To realistically reproduce the system, AFM images are vectorized to generate representative nanoparticle geometries. The simulated hysteresis loops, incorporating particle size distributions and interparticle interactions, show strong agreement with experimental results. The results demonstrate that the interplay between surface oxidation exhibits remarkable chemical and magnetic stability, preserving ferromagnetic properties under ambient conditions. These results demonstrate that nanovoid-engineered oxide architectures can serve as active platforms for simultaneously controlling nanoparticle growth, oxidation behavior, and magnetic response.