Microstructure and electromagnetic performance of the FeCoAlON films tuned by N2 pressure during reactive pulsed laser deposition

Highlights: • FeCoAlON magnetic composite films are first prepared by reactive pulsed laser deposition. • The introduction of N₂ leads to shrunken FeCo nanoparticles and thickened insulating layers. • The films transforms from ferromagnetic to superparamagnetic with shrunken nanoparticles and thickened insulating layers. • The obtained FeCoAlON films have excellent comprehensive electromagnetic properties with proper N₂ pressure. FeCoAlON films were fabricated by reactive pulsed laser deposition. The microstructure and electromagnetic properties have been investigated as a function of N₂ pressure, which was varied from 0 to 5 mtorr. All the FeCoAlON films contains ultrafine FeCo nanoparticles isolated by nonmagnetic insulating layers. Those insulating layers ensure high electrical resistivity of the films and will be transformed from Al₂O₃ into AlN with increasing N₂ pressure. The oxidation of Fe and Co can be effectively suppressed by introducing N₂. The Fe tends to form amorphous iron nitrides at higher N₂ pressures, leading to different magnetic response. Optimized electromagnetic properties can be achieved under 3 mtorr of N₂, showing great potential in noise suppression application at high frequencies. Further increased N₂ pressure to 5 mtorr leads to shrunken FeCo nanoparticles and thickened insulating layers due to the formation of nonmagnetic iron nitrides, giving rise to superparamagnetic response of the FeCoAlON thin film. Consequently, appropriate N₂ pressure plays an essential role in inducing favorable microstructure and phase composition for enhanced electromagnetic performance.