Crystallographic and Magnetic Properties of R₂ Fe₁₇C_x with R=Y, Pr, Nd, Sm, Gd, Dy, and Er

A series of R₂ Fe₁₇C_x compounds (R=Y, Pr, Nd, Sm, Gd, Dy, and Er; x=0, 0.5 and 1.0) were synthesized. X-ray diffraction analyses showed that the crystal structure is rhombohedral Th₂Zn₁₇ type for R=Pr, Nd, Sm, and Gd. For R=Y, Dy and Er, a structure transformation from hexagonal Th₂Ni₁₇ type (x=0.5) to rhombohedral Th₂Zn₁₇ type (x=1.0) was observed. The introduction of C into R₂Fe₁₇ leads to an expansion of the lattice. It strongly enhances Curie temperature. C atoms occupy interstitially the nearest neighbour sites to the R atoms in the lattice. The anisotropy of R sublattice was strengthened. A uniaxial anisotropy was observed in Sm₂Fe₁₇C_0.5 at room temperature.