Framework for fabricating quality magnetoelastic thin films, FeGa as an example

Fabrication of magnetostrictive FeGa thin films with reliable properties remains challenging due to compositional variations, crystal structure, surface roughness, and residual stresses that strongly modify magnetoelastic behavior. This challenge is further complicated by the difficulty of measuring the film's magnetostrictive response. This study systematically investigates Fe85Ga15 films (100 and 250 nm) sputtered on Si and PMN–PT {[PB(Mg1/3Nb2/3)O3]0.68(PbTiO3)0.32} substrates at varying sputtering powers, argon pressures, and Cu or Ta buffer layers. X-ray diffraction indicates the presence of the disordered A2 phase. Residual stresses range from −150 to +350 MPa and strongly influence magnetic hardness and magnetoelastic performance. Cu buffer layers yield smoother film surfaces (Ra = 0.1 nm) and a softer/superior magnetic response compared to Ta layers (Ra = 1.12 nm). Magnetostriction was evaluated using both an indirect energy-based method and a direct cantilever beam measurement. Direct measurements show strains of ∼80 ppm for 100 nm and ∼40 ppm for 250 nm Fe85Ga15 films, while energy-based estimates give 55 and 24 ppm, respectively. These findings establish and describe a generalizable framework for the fabrication and comprehensive characterization of magnetostrictive thin films, applicable beyond the specific FeGa system studied here.