Magnetic Properties and Microstructure of Perpendicular ${\rm FePt}({\rm B}_{4}{\rm C-Ag})$ Granular Films

Multilayers [FePt(2.5 nm)/B₄C(t nm)]₄ (t = 0-1) and [FePt(2.5 nm)/(B₄C)_0.7Ag_0.3(0.25 nm]₄ were alternately deposited on a glass substrate and subsequently annealed using a rapid thermal process (RTP) at 800°C for 3 min. Thereafter, granular FePt(B₄C) and FePt(B₄C-Ag) films with perpendicular magnetization were formed. The immiscible B₄C, Ag) elements were used as a segregant to isolate FePt grains and maintain c-axis alignment. B₄C is an extremely covalent hard ceramic material with a high melting point, and it is used to separate FePt grains and prevent the formation of soft FeB during annealing. The minor doped Ag with high mobility was used to promote the ordering. The FePt grains were separated uniformly, and the average grains size was 14.7 nm in the (Fe_0.48Pt_0.52)₉₀[(B₄C)_0.7Ag_0.3)]₁₀ film. Furthermore, the FePt grains were strong separated, and the grains size was reduced to 10.6 nm in annealed [FePt(1 nm)/(B₄C)_0.2Ag_0.8(0.1 nm)]₁₀ multilayer.