Monolayer assembly of ferrimagnetic Co(x)Fe(3-x)O4 nanocubes for magnetic recording.

We report a facile synthesis of monodisperse ferrimagnetic Co(x)Fe(3-x)O4 nanocubes (NCs) through thermal decomposition of Fe(acac)3 and Co(acac)2 (acac = acetylacetonate) in the presence of oleic acid and sodium oleate. The sizes of the NCs are tuned from 10 to 60 nm, and their composition is optimized at x = 0.6 to show strong ferrimagnetism with the 20 nm Co0.6Fe2.4O4 NCs showing a room temperature Hc of 1930 Oe. The ferrimagnetic NCs are self-assembled at the water-air interface into a large-area (in square centimeter) monolayer array with a high packing density and (100) texture. The 20 nm NC array can be recorded at linear densities ranging from 254 to 31 kfci (thousand flux changes per inch). The work demonstrates the great potential of solution-phase synthesis and self-assembly of magnetic array for magnetic recording applications.