Magnetic properties of FePt nanoparticle assemblies embedded in atomic-layer-deposited Al₂O₃

Self-assembled face-centered cubic FePt nanoparticles on Si substrates were embedded into amorphous Al₂O₃ capping layers with various thicknesses in the range 5-20 nm using atomic layer deposition (ALD) technology. The effect of the Al₂O₃ layer thickness on the structure, mono-dispersibility, and magnetic properties of the FePt/Al ₂O₃-matrix composite films was investigated. After annealing at 700°C in a reducing atmosphere for 1 h, well-dispersed face-centered tetragonal (fct) FePt particles could be obtained for the samples with 10 nm-thick and greater Al₂O₃ layers. Experimental results suggest that the protection of the amorphous 10 nm-thick Al ₂O₃ matrix can effectively inhibit grain growth and particle aggregation, and preserve the ordered domains of FePt nanoparticles during the L1₀ ordering transition through annealing. The 5 nm fct FePt-nanoparticles/10 nm-thick Al₂O₃-matrix sample shows higher coercivity of 5.9 kOe. The combination of ALD-capping layer and self-assembled FePt nanoparticles provides a potential new approach to fabricate patterned magnetic recording media with ultrahigh areal density.