MAGNETIC DOMAIN PERCOLATION IN GRANULAR CO-AG

The most dramatic changes in the properties of granular metals occur n ear the percolation threshold x(c), which generally occurs at a volume fraction of approximately 0.50. There has been much speculation conce rning the evolution of magnetic domains at x(c), however, no direct ob servations have been produced. Using scanning electron microscopy with polarization analysis, we investigate the formation of domains in a s eries of granular Co-Ag samples. We find x(c) to lie in the range [0.5 0, 0.55], and we report on the size and morphology of the observed dom ains. Below x(c), a domain pattern appears which may be due either to interparticle correlations or to residual Co in the silver matrix; we have previously discussed the ramifications of this observation on an understanding of GMR. In this paper, we place limits on the latter of these two models. Above x(c), the domains resemble ''stripe domains'' which have been observed in amorphous materials. This observation sugg ests the presence of anisotropy perpendicular to the film plane. (C) 1 996 American Institute of Physics.