Effect of post-deposition annealing atmosphere on ECR-sputtered Fe₃O₄ thin films and micromagnet fabrication

Abstract In this study, Fe 3 O 4 thin films were synthesized on semi-insulating GaAs (001) substrates using electron cyclotron resonance (ECR) sputtering, followed by three different post-deposition annealing: unannealed, Ar atmosphere at 400 °C, and Ar + H 2 atmosphere at 400 °C. Micromagnets were fabricated by first patterning the resist using photolithography, then depositing Fe 3 O 4 via ECR sputtering, followed by lift-off to define the micromagnet structures, and finally applying post-deposition annealing. Surface morphology and elemental composition were characterized using scanning electron microscopy and energy-dispersive X-ray spectroscopy. X-ray photoelectron spectroscopy was used to investigate oxidation states, while magnetic properties were evaluated via superconducting quantum interference device magnetometry. Among all samples, the one annealed in Ar at 400 °C showed the best balance of Fe 3 O 4 -like stoichiometry, magnetic stability, and well-defined switching behavior. Although the film remained amorphous due to the low deposition temperature, it exhibited strong ferromagnetic response suitable for spintronic applications. This micromagnet structure holds strong potential as a ferromagnetic source/drain for future planar spin valve devices, benefiting from Fe 3 O 4 ’s high spin polarization and scalability.