ENHANCED MAGNETIC-ANISOTROPY AT THE PERCOLATION-THRESHOLD OF FE-SIO2 COMPOSITE THIN-FILMS

Ferromagnetic resonance (FMR) measurements at 9.6 GHz and room temperature are reported for very thin (50 Å) sputtered films of Fe-SiO2 with volume fractions of Fe, f, spanning the percolation threshold at f c=0.57. It is inferred from the FMR linewidths that the magnetic anisotropy of the percolating composite of Fe particles peaks at fc. Possible mechanisms for this anisotropy enhancement are examined and it is argued that the shape anisotropy of the percolation clusters may be the principal contribution. These results and our interpretations provide a possible explanation for the peak in the coercivity near the percolation threshold of Fe-SiO2 composite films recently reported by S. H. Liou and C. L. Chien [Appl. Phys. Lett. 52, 512 (1988)].