The interstitial carbides of Er2Fe17Cx with x = 0.0, 0.5, 1.0, 1.5, 2.
0, 2.5 and 3.0 have been synthesized by arc melting and by the Gas-Pha
se Interaction (GPI) method. The unit-cell volume of the compounds is
found to increase with increasing carbon concentration. The dependence
of Curie temperatures, spin-reorientation temperatures and the magnet
ic coupling on the carbon content has been investigated. The spin phas
e diagram of the series is given.