Segregated microstructure growth in sputtered Co-Cr films

The growth process of a latent segregated microstructure called the CP (chrysanthemumlike pattern) has been investigated as a function of film thickness in sputtered Co-21.5 at.% Cr films. As film growth proceeds, each crystallite exhibits CP structure development with a periodical stripe pattern. Only crystallites with Cr-rich cores survive. This is related to Cr segregation at the grain boundaries. The CP structure growth process is explained using a model based on (1) a phase separation process restricted by grain boundary and surface diffusion, and (2) grain boundary Cr enrichment at the latter stage of segregation. The correlation between CP structure growth and the change in magnetic properties strongly indicates that the perpendicularly formed CP structure is responsible for the magnetic properties of Co-Cr films. >