Magnetic properties and microstructure study of high coercivity Au/FePt/Au trilayer thin films

High-coercivity Au(60 nm)/FePt(delta nm)/Au(60 nm) trilayer samples were prepared by sputtering at room temperature, followed by post annealing at different temperatures. For the sample with delta = 60 nm, L1(0) ordering transformation occurs at 500 degrees C. Coercivity (H-c) is increased with the annealing temperature in the studied range 400-800 degrees C. The H-c value of the trilayer films is also varied with thickness of FePt intermediate layer (delta), from 27 kOe for delta = 60 nm to a maximum value of 33.5 kOe for delta = 20 nm. X-ray diffraction data indicate that the diffusion of Au atoms into the FePt L1(0) lattice is negligible even after a high-temperature (800 degrees C) annealing process. Furthermore, ordering parameter is almost unchanged as delta is reduced from 60 to 15 nm. Transmission electron microscope (TEM) photos indicate that small FePt L1(0) particles are dispersed amid the large-grained Au. We believe that the high coercivity of the trilayer sample is attributed to the small and uniform grain sizes of the highly ordered FePt particles which have perfect phase separation with Au matrix. (C) 2006 Elsevier B. V. All rights reserved.