<p>Amorphous cobalt–iron–gadolinium (Co₄₀Fe₄₀Gd₂₀) thin films with thicknesses ranging from 10 nm to 50&#xa0;nm were deposited on silicon (Si)(100) and glass substrates by direct-current (DC) sputtering and subsequently annealed at temperatures between 100°C and 300°C. X-ray diffraction (XRD) analysis confirmed that all films retained an amorphous structure after annealing. X-ray photoelectron spectroscopy (XPS) revealed oxygen uptake, particularly for films deposited on glass substrates, reaching approximately 25% at 300°C. This oxidation was accompanied by partial reduction of cobalt (Co) and iron (Fe), as well as a noticeable loss of gadolinium (Gd). Magnetic measurements showed soft magnetic behavior, with coercivity (Hc) values below 40 Oe. The saturation magnetization (Ms) exhibited a slight increase with annealing temperature, while the squareness ratio increased from 0.12 to 0.19 at 300°C, indicating enhanced magnetic anisotropy. Electrical measurements demonstrated stable resistivity up to 200°C, followed by a pronounced increase at 300°C due to oxidation effects. Carrier mobility varied as a function of both annealing temperature and film thickness. Overall, moderate annealing effectively preserves the electrical and magnetic properties of CoFeGd thin films, whereas excessive thermal treatment enhances magnetic anisotropy but degrades electrical conductivity. These findings provide important guidance for optimizing CoFeGd thin films for spintronic and flexible magnetic device applications.</p> Graphical Abstract <p></p>