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 over growth of alpha-Fe on Pt "seed" particles epitaxially grown on (100) NaCl a nd MgO substrates and the ordering reaction between Fe and Pt upon annealin g at temperatures higher than 500 degrees C. The coercivities of the anneal ed (600 degrees C for 6 h) a-Al2O3/Fe(1 nm)/Pt (1.5 nm) films on both the N aCl (100) and MgO (100) substrates are higher than 3.3 kOe. Transmission el ectron microscopy observation showed that the film consisted of oriented L1 (0) FePt island-like crystals with an average size of 12 nm and a separatio n of 4 nm. It was found that any one of the three < 100 > axes of the fcc P t parent particles could act as the tetragonal c axis of the L1(0) FePt sup erstructure and all three-variant ordered crystalline domains of the tetrag onal 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].