Ordering of island-like FePt crystallites with orientations

Thin films of oriented island-like crystallites of L10 FePt separated by amorphous (a-)Al2O3 were fabricated. The process took advantage of the overgrowth of α-Fe on Pt “seed” particles epitaxially grown on (100) NaCl and MgO substrates and the ordering reaction between Fe and Pt upon annealing at temperatures higher than 500 °C. The coercivities of the annealed (600 °C for 6 h) a-Al2O3/Fe(1 nm)/Pt (1.5 nm) films on both the NaCl (100) and MgO (100) substrates are higher than 3.3 kOe. Transmission electron microscopy observation showed that the film consisted of oriented L10 FePt island-like crystals with an average size of 12 nm and a separation of 4 nm. It was found that any one of the three 〈100〉 axes of the fcc Pt parent particles could act as the tetragonal c axis of the L10 FePt superstructure and all three-variant ordered crystalline domains of the tetragonal L10 phase could exist in the small 10-nm-size FePt crystallites. The high magnetic coercivity of the film, with well-separated FePt particles, can be attributed to the ordering (L10) as well as the oriented nature of the FePt crystallites.