The diffusion of Cu and Cr through 100nm-thick Co films was investigated, using X-ray photoelectron spectroscopy, at temperatures ranging from 300 to 400C. The grain boundary diffusivities were determined by modelling the accumulation of Cu or Cr on Co surfaces as a function of time at a given temperature. It was found that the grain boundary diffusivity of Cu through Co could be described by:

D (cm2/s) = 2 x 104exp[-2.4(eV)/kT]

Similarly, Cr grain boundary diffusion through Co thin films could be described by:

D (cm2/s) = 6 x 10-2exp[-1.8(eV)/kT]

Extensive grain growth and texturing of the magnetic film occurred during annealing when Co was deposited onto a Cu under-layer. This was believed to affect the grain boundary diffusion. On the other hand, the microstructure of Co which was deposited on a Cr under-layer remained relatively unchanged during annealing. The difference in grain growth between the 2 bi-layers was suggested to account for the large difference in activation energies. Magnetometer measurements showed that an increased in-plane coercivity, a reduced remanence squareness and a reduced coercive squareness resulted from the grain boundary diffusion of Cu and Cr.

J.G.Pellerin, S.G.H.Anderson, P.S.Ho, C.Wooten, K.R.Coffey, J.K.Howard, K.Barmak: Journal of Applied Physics, 1994, 75[10], 5052-60