Non-stoichiometric FePt nanoclusters for heated dot magnetic recording media

Abstract

Heated dot magnetic recording (HDMR) provides a path to increase the areal density of magnetic recording media beyond 4 Tb/in². HDMR-based recording media requires ultrasmall, noninteracting, and thermally stable magnetic dots with high perpendicular anisotropy. We have synthesized nonstoichiometric Fe₆₀Pt₄₀ nanoclusters with and without a Pt buffer layer on silicon substrates, which shows a reduction in chemical ordering temperatures. The Fe₆₀Pt₄₀ nanoclusters retain the hard magnetic phase up to 1023 K with the coercive field of 1.3 Tesla due to the Pt element compensation from the buffer layer. This compensation of Pt was confirmed through X-ray diffraction (XRD) investigations where two distinct phases of Fe₃Pt and FePt₃ are observed at elevated annealing temperatures. Micromagnetic simulations were performed to understand the effect of magnetic anisotropy, dipolar interaction, and exchange coupling between the soft magnetic Fe₃Pt and hard magnetic FePt. The results imply that nonstoichiometric Fe₆₀Pt₄₀ with the Pt buffer layer facilitates low chemical ordering temperatures retaining the high perpendicular anisotropy with minimal noninteracting behavior, suitable for HDMR.