Material and layer design to overcome writing challenges in bit-patterned media

In this paper, the problem of writability in bit-patterned media (BPM) for high areal density will be discussed. A new film structure is proposed, made of a composite in-plane and perpendicular anisotropy layers to improve writability and reduce the time of magnetization switching in BPM. To demonstrate the efficiency of an in-plane anisotropy layer in assisting the switching of the magnetization of the high perpendicular anisotropy recording layer, we use micromagnetic simulation to study magnetization reversals in BPM for 5 Tb/in$^{2}$. Experiments have been carried out on patterned arrays of 60-nm-size dots made of [Co(0.3 nm)/Pd(0.8 nm)]$-{\times 15}$ multilayer and Co(2 nm)/[Co(0.3 nm)/Pd(0.8 nm)]$-{\times 15}$ composite structure. The mean switching field calculated from remanence magnetization curves shows a reduction of more than 50% from its initial value by adding a 2-nm-thick Co bottom layer with in-plane anisotropy. No difference in switching field distribution was observed in the two structures studied, indicating the merit of assisting the switching of high anisotropy patterned media by exchange coupling to an in-plane anisotropy layer.