ATOMIC DIFFUSION IN AMORPHOUS GD-FE THIN-FILMS

We have investigated atomic diffusion in RF-sputtered amorphous Gd-Fe thin films using Auger Electron Spectroscopy (AES). Polycrystalline Co films were deposited in-situ on amorphous Gd-Fe films. These bilayer films were vacuum annealed to induce atomic diffusion of Co into the amorphous Gd-Fe films. AES depth profiles were used to calculate diffusion lengths (Dat a)1/2 where ta is the annealing time, D a is the diffusion coefficient Daoexp(-Q a/KT), and Qa is the activation energy. We found that Dao=10-3cm2/sec and Q a=1.3 eV suggesting that amorphous Gd-Fe films behave like a liquid phase. Diffusion lengths of 150-250 Å were determined after annealing at 200-300°C for 3 hours. These results suggest that amorphous Gd-Fe films are porous. In agreement, AES depth profiles show that amorphous Gd-Fe films exposed to air possess an oxide surface layer 500-1000 Å thick. Electron diffraction studies showed that the outer halo becomes very sharp after annealing at 300°C for 3 hours. Dark-field microscopy showed that inner halo is still due to an amorphous matrix. However, according to x-ray microanalysis, the outer halo is associated with microcrystallization of Fe. According to our diffusion studies, such an amorphous phase separation can easily develop during sputter-induced surface diffusion to produce perpendicular magnetic anisotropy.