Surface modification of FePt(Ag, C) granular film by ultrathin B4C capping layer

• Published in: Applied surface science 2020-04, Vol.509, p.145337, Article 145337
• Main Authors: Tsai, Jai-Lin, Weng, Shi-Min, Dai, Cheng, Chen, Jyun-You, Huang, Lin-Chen, Hsu, Ting-Wei
• Format: Article
• Language: English
• Subjects: Coercivity; Ordering degree; Perpendicular magnetic anisotropy
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2020.145337

•Perpendicular magnetic anisotropy was enhanced by B4C capping layer.•Out-of-plane coercivity was increased by B4C capping layer.•Ordering degree and surface roughness were improved by B4C capping layer.•The B, C, N elements were segregated in FePt grains and boundaries. The in-plane magnetic component in FePt-40 vol% (Ag, C) granular film was caused by lower ordering degree which lower the magnetic anisotropy field and out-of-plane coercivity (Hc = 23.6 kOe). To inhibit the FePt grains with second nucleation, random texture and in plane c-axis, the ultrathin B4C layer with thickness of 1 nm was capped. After surface modification, the FePt-40 vol% (Ag, C) film illustrates high perpendicular magnetic anisotropy (Ku = 1.75 × 107 erg/cm3) and out-of-plane coercivity (Hc = 28.8 kOe). The in-plane remanence magnetic moment is small and the tiny magnetization kink at zero field was not observed in easy-axis loop of 6 nm thick FePt-40 vol% (Ag, C) film. The ordering degree and the average surface roughness of FePt-(Ag, C) films were improved by surface diffusion of B4C which deposited at 470 °C and post-annealed for 2 min. Further, the perpendicular magnetic anisotropy and out-of-plane coercivity of FePt-(Ag, C) films were enhanced significantly. The TiOx are more favorable than TiN in MgTiON layer due to formation enthalpy, part of N atoms was diffused and incorporated in the FePt lattice evidenced in high angle angular dark field mapping. After post annealing, the released N atoms cause lots of vacancies and defects inside FePt film which promote the ordering degree.