Oxygen Effects on Magnetic Properties and Microstructure of FePt(B, Ag) Granular Films

Multilayers [FePt(1 nm)/(B_0.7Ag_0.3)(0.1 nm)]₁₀ were alternately deposited on a glass substrate and subsequently annealed using a rapid thermal process (RTP) at 800°C for 3 min. Plasma oxidation process was performed on a sputtered (B, Ag) layer. Thereafter, granular FePt(B, Ag) films with perpendicular magnetization were formed. The immiscible (B, Ag) elements were used as a segregant to isolate FePt grains and maintain c-axis alignment. After plasma oxidation and posting annealing, the iron-oxide and boron-oxide were indexed in granular FePt(B, Ag) films. When the oxygen flow ratio was within 1%, the FePt(B, Ag) films show maze-like structures with interconnected grains after plasma oxidation. The oxygen may create vacancies that improve the atomic diffusion during ordering and enhance the grain growth. When the oxygen flow ratio was above 3%, the FePt grain size was furthered reduced to around 4 ~ 5 nm due to the formation of boron oxide. However, the perpendicular magnetization and coercivity of Fe(B, Ag) film deteriorated due to the formation of soft magnetic iron-oxide during postannealing.