Ordering of island-like FePt crystallites with orientations

Thin films of oriented island-like crystallites of L1(0) FePt separated by amorphous (a-)Al2O3 were fabricated. The process took advantage of the overgrowth of alpha-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 degrees C. The coercivities of the annealed (600 degrees 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 L1(0) 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 L1(0) FePt superstructure and all three-variant ordered crystalline domains of the tetragonal L1(0) 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 (L1(0)) as well as the oriented nature of the FePt crystallites. (C) 1999 American Institute of Physics. [S0003-6951(99)03149-6].