Microstructure and coercivity of granular FePt-AlN thin films

(FePt)(100-x)-(AlN)(x) (x = 0-50 vol%) granular films were prepared by DC and RF magnetron co-sputtering of FePt and AlN targets, then annealed in vacuum at various temperatures. Transmission electron microscopy analysis shows that the structure of the film is granular FePt particles embedded in amorphous AlN matrix and the FePt particle in as-deposited film is face-centered-cubic gamma -phase and in the high coercivity annealed film is face-centered-tetragonal gamma (1)-phase. The particle size of FePt in annealed film was increased with the annealing temperature and film thickness but decreased with increasing AlN content. The magnetic anisotropy of the film was parallel to the film plane. The coercivity of the FePt-AlN film was dependent on the annealing temperature, the AlN volume fraction, and film thickness. It was found that the optimum annealing temperature for obtaining highest coercivity of the film is increased with AlN content. The in-plane coercivity of the film could reach to about 8 kOe for the (FePt)(70)-(AlN)(30) film after annealing at 750 degreesC for 30 min. (C) 2001 Elsevier Science B.V. All rights reserved.