Improvement of environmental stability by doping beryllium in TbFeCo magnetooptical recording media

The effect of doping beryllium and the improvement of environmental stability with respect to oxidation of terbium in TbFeCo magnetooptical recording media was examined by measuring temporal changes in magnetooptical and magnetic properties in the accelerating environments of 120°C in air and 80°C, 90% relative humidity. In comparison with other dopant elements such as aluminium, chromium, and titanium, beryllium was most effective for protecting the medium from oxidation with less degradation of properties even at doses greater than 25 at.%. In addition, an electrochemical corrosion test was performed by measuring corrosion potential against a standard calomel electrode by immersing the samples in a 0.1 N NaClO₄ electrolytic solution. Contrary to the authors´ expectation, Be-doped films were the most soluble in the electrolytic solution among the films containing dopant elements. This situation can, however, be considerably improved by adding a few percent of another active element together with a reduced amount of beryllium, for instance, 11.3 at.% Be+5.6 at.% Cr