Ledge-type Co/L1-FePt exchange-coupled composites

FePt-based exchange-coupled composites consisting of a magnetically hard L1₀-FePt phase exchange-coupled with a soft ferromagnetic material are promising candidates for future ultra-high density (>1 Tbit/in²) perpendicular magnetic recording media, also being of interest for other applications including spin torque oscillators and micro-electro-mechanical systems, among others. In this paper, the effect of the thickness of a soft Co layer (3 < th_Co < 20 nm) on the magnetic behavior of ledge-type fcc(100)-Co/L1₀(001)-FePt composites deposited on an MgO (100) substrate is systematically studied by combining morpho-structural analyses and angular magnetization measurements. Starting from a film consisting of isolated L1₀(001)–FePt islands, the ledge-type structure was obtained by depositing a Co layer that either covered the FePt islands or filled-up the inter-island region, gradually forming a continuous layer with increasing Co thickness. A perpendicular anisotropy was maintained up to th_Co ∼ 9.5 nm and a significant reduction in the coercivity (about 50% for th_Co ∼ 3 nm) with the increase in th_Co was observed, indicating that, by coupling hard FePt and soft Co phases in a ledge-type configuration, the writability can be greatly improved. Recoil loops' measurements confirmed the exchange-coupled behavior, reinforcing a potential interest in these systems for future magnetic recording media.