FORMATION AND MAGNETIC-PROPERTIES OF THE COMPOUNDS R2FE14C

It was shown by X-ray diffraction that rare earth compounds of the type R2Fe17 can dissolve appreciable amounts of carbon up to x=0.6 in R2Fe17Cx at 900°C. The increase in the lattice constants is accompanied by a strong increase in Curie temperature. From a structure determination (R=7%) it was found that the carbon atoms dissolve interstially and occupy the 9e position in the Th2Zn17 structure type (R3¯m). This ternary carbide is present as the main phase when compounds of the type R2Fe14C are heated above their decomposition temperatures. The decomposition proceeds by means of a solid state transformation and the corresponding transformation temperatures Tt vary strongly with the R component. In several of the light rare earth systems Tt becomes rather low and makes an annealing treatment ineffective with regard to the formation of R2Fe14C phases. The magnetic properties of the R2Fe14C phases are compared with those of R2Fe14B. It is shown that the former follow the magnetic behavior of the latter almost completely.