Improvement of corrosion resistance of GdTbFe by metal coatings

For an application of rare earth (RE) transition metal (TM) alloys for erasable optical recording the corrosion sensitivity has to be limited in order to obtain long-term stability. The use of thin RE-TM films as a storage medium needs a top coating to avoid strong surface-induced change of intrinsic material properties due to oxidation. This paper presents annealing experiments of GdTbFe films in air within the temperature range of 65 to 160 °c. The GdTbFe films of 40 and 80 nm thickness were coated with Al,Cr,CrNi and Cu coatings of 50 and 200 nm thickness, respectively. The values of coercivity and the angular dependence of torque were measured in the initial state right after the preparation of samples. These values were compared with the results of the annealed films. The angular dependence of torque and the corresponding oxygen depth profiles (SIMS) show different results for the coated and non-coated samples. Coatings of Cr or Al having 20 or 50 nm thickness both are suitable being an excellent barrier against the diffusion of oxygen into the magnetic layer.