Stability Test of GdTbFe at High Temperatures

The reliability of rare earth-transition metal (RE-TM) alloy films with a multilayer structure, which attain a high signal-to-noise ratio, is discussed. In order to study the stability of multilayer magneto-optic (M-O) media which consist of a GdTbFe layer sandwiched between nitride layers, heating tests (380-480°C) have been conducted. Magneto-optic properties were evaluated using Kerr hysteresis loops. In a high-temperature environment (400°C), the coercive force (Hc) is found to increase, while the Curie temperature (Tc) decreases. It seems that these changes in Hc and Tc result from a decrease in effective RE content. However, samples using SUS-304 as a reflector exhibit less change in Hc than those using Al at 400°C, and samples heated in vacuum (2×10^¿6 Torr) exhibit a small change in Hc. From these results, it is felt that such phenomena in high temperature environments are caused by selective oxidation of RE atoms. There is little change in the magneto-optic properties at 380°C. Therefore, multilayer M-O media using AlN offer promise as high-stability materials for use in thermomagnetic recording.