(a) Curie temperatures of R₂Fe₁₇C_x ribbons (x = 0, 1.0, 1.5, and 2.0); (b) Curie temperatures versus unit cell volume of Er₂Fe₁₇C_x and Tm₂Fe₁₇C_x; (c) dependence of M_s on carbon content of R₂Fe₁₇C_x ribbons.^[147–157]