Microstructural and magnetic studies of L1 0 FePt–SiO 2 nano-composite thin film with columnar structure for perpendicular magnetic recording

Abstract

(Fe 50Pt 50) 100− x -(SiO 2) x films ( x=0–30 vol%) were grown on a textured Pt(0 0 1)/CrRu(0 0 2) bilayer at 420 °C using glass substrates. FePt(0 0 1) preferred orientation was obtained in the films. Interconnected microstructure with an average grain size of about 30 nm is observed in the binary FePt film. As SiO 2 is incorporated, it precipitates as particles are dispersed at FePt grain boundaries. When the content of SiO 2 is increased to 13 vol%, columnar FePt with (0 0 1) texture separated by SiO 2 is attained. The FePt columns have a length/radius ratio of 2:1. Additionally, the mean grain size is reduced to about 13 nm. The development of this well-isolated columnar structure leads to an enhancement in coercivity by about 44% from 210 to 315 kA/m. As the SiO 2 content exceeds 20 vol%, a significant ordering reduction is found accompanied by a transformation of preferred orientation from (0 0 1) to (2 0 0) and the columnar structure disappears, resulting in a drastic degradation in magnetism. The results of our study suggest that isolated columnar, grain refined, (0 0 1)-textured FePt film can be achieved via the fine control of SiO 2 content. This may provide useful information for the design of FePt perpendicular recording media.