Interplay of Surface Morphology and Thermal Annealing on the Multifunctional Performance of Amorphous CoFeBGd Thin Films

Amorphous cobalt-iron-boron-gadolinium (Co40Fe40B10Gd10) thin films were deposited on glass and silicon (Si) (100) substrates to investigate the effects of thermal annealing at 100–300°C on their structural, surface, mechanical, optical, magnetic, and electrical properties. X-ray diffraction (XRD) confirmed that the films maintained an amorphous structure up to 300°C, highlighting the stabilizing roles of boron (B) and gadolinium (Gd). Atomic force microscopy (AFM) revealed that surface roughness initially increased and then decreased, reaching 0.54 nm on glass and 0.85 nm on Si at 300°C, which strongly influenced the films’ multifunctional behavior. After annealing at 300°C, 50 nm-thick films exhibited a hardness of 13.1 GPa and a Young’s modulus of 195 GPa, while 10 nm-thick films maintained a transmittance of 39%. Soft magnetic behavior was observed, with the saturation magnetization (Ms) peaking at 200°C for films on glass and at 300°C for films on Si. Hall measurements revealed substrate-dependent charge transport, showing higher carrier mobility on glass and higher carrier concentration on Si. These results demonstrate that thermal annealing and substrate selection can effectively tune the structural, mechanical, optical, magnetic, and electrical properties of amorphous CoFeBGd thin films, making them promising candidates for flexible, spintronic, and optoelectronic applications.