Effects of Additive Elements on Corrosion Resistance of RE-TM Films

Abstract

Rare earth-transition metal amorphous films are promising for erasable optical memory media. However, they have the drawback of poor reliability due to the poor corrosion resistance. The corrosion of the films is classified as being surface oxidation, selective oxidation of RE metals, and pitting corrosion. We have studied the corrosion behavior and succeeded in improving the corrosion resistance. To improve corrosion resistance, one of the elements, Co, Ni, Pt, Al, Cr, and Ti, is added to Tb-Fe and Tb-Co films by simultaneous sputtering. The films (no protection) are subjected to an accelerated aging test. The elements are classified into two groups: (Co, Ni, and Pt) and (Al, Cr, and Ti). The former group elements are only effective in preventing surface oxidation and pitting corrosion. The latter group elements, however, are effective in inhibiting corrosion of all the above modes. This high corrosion resistance can be explained in terms of to their ability to getter oxygen and to form passive states. The degree of these effects, in order of strength, is Cr Ti Al. These additives cause no appreciable change in the magnetooptical properties.