Bi-layer thin films of Nb and Permalloy were annealed at 100 to 450C. It was found that Ni diffused strongly from the Permalloy and into the Nb layer. As a result, the electrical resistance of the bi-layer thin films and the coercivity of the Permalloy layers increased with increasing annealing temperature. The interdiffusion of Ni and Nb increased with decreasing film thickness. This was attributed to short-circuit diffusion along the grain boundaries, because the thin metal layers consisted of small grains. The apparent activation energies for interdiffusion were 0.74eV for Nb(50nm)/Ni-Fe(80nm) bi-layer thin films, to 0.64eV for Nb(30nm)/Ni-Fe(20nm) films and to 0.50eV for Nb(10nm)/Ni-Fe(12nm) films.

K.Yamamoto, M.Kitada: Thin Solid Films, 1994, 252[2], 135-8