Degradation of magneto-optic media by preferential oxidation of the rare-earth component, typically Tb. is a serious limitation to their lifetime and utility. In this paper, we present data on diffusion studies of 0 and TbFeCo through thin overlayers of a series of metals with differing electronegativities. Samples of TbFeCo were overcoated with Sm. Gd, Zr, Ni. or Pt, then vacuum transferred to an x-ray photoelectron spectrometer (XPS). Heating in situ was used to accelerate the diffusion process, and XPS to determine the extent of the diffusion. After 20 hours, the samples were depth profiled to further examine the effects of heating. The metals with the lowest electronegativities, Sm and Gd. provided the greatest resistance to Tb diffusion; however. it was noted that partial oxidation of these metals occurred during their deposition. These data suggest the use of thin rare-earth oxide diffusion barriers in connection with thick refractory overlayers for the protection of MO media.