Structure and magnetic properties of the R2Fe17‐based quasiternary compounds (R=Sm, Er, Gd, Y, Pr, Nd; M=Al, Ga) and their nitrides have been investigated. The saturation magnetization of R2Fe17−xMxcompounds decreases with the increasing M content, while the M concentration dependence of the Curie temperature exhibits a maximum at aboutx=3.0 for the parent compounds. By nitrogenation the lattice parameters, the saturation magnetization, and the Curie temperature all have a corresponding increase compared with the parent alloys. The volume effects on the Curie temperature of these compounds have been studied. Thed ln Tc/d ln Vvalues were derived by comparing the change of the Curie temperature and volume before and after nitrogenation and show a linear dependence on the Curie temperatures for these systems investigated. This behavior can be quite well understood in terms of a combined model of localized and itinerant electrons suggesting more than 90%delectrons are localized, The same conclusion can be obtained from a analysis of the exchange fieldHexdependence of the iron sublattice magnetization in the R2Fe17compounds and their nitrides, and the iron proportionality constantVFebefore and after nitrogenation. ©1996 American Institute of Physics.