GRAIN-BOUNDARY DIFFUSION AND ITS EFFECTS ON THE MAGNETIC-PROPERTIES OF CO CU AND CO CR THIN-FILM BILAYERS

X-ray photoelectron spectroscopy has been used to investigate grain boundary diffusion of Cu and Cr through 1000-angstrom-thick Co films in the temperature range of 300-400-degrees-C. Grain boundary diffusivities were determined by modeling the accumulation of Cu or Cr on Co surfaces as a function of time at fixed annealing temperature. The grain boundary diffusivity of Cu through Co has a diffusion coefficient D0,gb of 2x10(4) cm2/s and an activation energy E(a,gb) of 2.4 eV. Similarly, Cr grain boundary diffusion through Co thin films exhibits a D0,gb of 6x10(-2) cm2/s and an E(a,gb) of 1.8 eV. The Co film microstructure has been investigated before and after annealing by x-ray diffraction and transmission electron microscopy. Extensive grain growth and texturing of the magnetic film occurred during annealing for Co deposited on a Cu underlayer which is believed to influence the grain boundary diffusion process. In contrast, the microstructure of Co deposited on a Cr underlayer remained relatively unchanged upon annealing. The difference in grain growth between the two bilayers has been suggested to account for the large disparity in activation energies. Magnetometer measurements have shown that increased in-plane coercivity H(c), reduced remanence squareness S, and reduced coercive squareness S* result from grain boundary diffusion of Cu and Cr into the Co films.