Influence of sputtering power and post-annealing on the structural, magnetic, and optical properties of CoFeNi–MgO–CoFeNi trilayer thin films

This work systematically investigates the combined effect of sputtering power and post-deposition annealing on the structural, chemical, magnetic, and optical properties of amorphous CoFeNi-MgO CoFeNi trilayer thin films deposited by the magnetron sputtering technique on glass substrates. In this regard, an explicit correlation has to be established between deposition parameters with multifunctional performance for the optimization of films in magneto-optical applications. The films were deposited under an Ar atmosphere (2.5 × 10⁻³ Torr) and post-annealed at 500 °C for 1 h under a nitrogen environment. High-resolution scanning electron microscopy(HRSEM) and Transmission electron microscopy(TEM) analyses demonstrated that increasing the sputtering power enlarged particle size from 63 ± 13 nm (75 W) to 157 ± 42 nm (130 W). The post-deposition annealing further promoted grain growth through thermal coalescence. Elemental analyses confirmed the presence of Co, Fe, and Ni elements as the main constituents along with oxygen due to surface oxidation. The annealing process also reduced the surface carbon contamination. The measurements from a Vibrating-sample magnetometer(VSM) indicated soft ferromagnetic behavior, with the maximum saturation magnetization (Mₛ = 12.05 emu/g) for the 100 W sample after the annealing process. UV–Vis spectroscopy indicated a reduction of the optical bandgap from 3.82 eV (75 W) to 2.73 eV (100 W) after annealing, and that the annealed samples exhibited consistently higher optical absorption than their unannealed counterparts. The results obtained establish a clear correlation between sputtering power and post-annealing treatment by showing combined enhancement effects in the magneto-optical properties, reducing the optical band gap, and improving interfacial quality in amorphous trilayer thin films.