The intermetallic compounds R2Co2SiC (R = Pr, Nd) were prepared from the reaction of silicon and carbon in either Pr/Co or Nd/Co eutectic flux. These phases crystallize with a new stuffed variant of the W2CoB2 structure type in orthorhombic space group Immm with unit cell parameters a = 3.978(4) Å, b = 6.094(5) Å, c = 8.903(8) Å (Z = 2; R1 = 0.0302) for Nd2Co2SiC. Silicon, cobalt, and carbon atoms form two-dimensional flat sheets, which are separated by puckered layers of rare-earth cations. Magnetic susceptibility measurements indicate that the rare earth cations in both analogues order ferromagnetically at low temperature (TC ≈ 12 K for Nd2Co2SiC and TC ≈ 20 K for Pr2Co2SiC). Single-crystal neutron diffraction data for Nd2Co2SiC indicate that Nd moments initially align ferromagnetically along the c axis around ∼12 K, but below 11 K, they tilt slightly away from the c axis, in the ac plane. Electronic structure calculations confirm the lack of spin polarization for Co 3d moments.

The intermetallic Nd 8 Co 4-x Al x Ge 2 C 3 (x ≈ 0.65) was prepared from reaction of germanium and carbon in Nd/Co eutectic flux in an alumina crucible. This phase exhibits a new structure type in orthorhombic space group Pbcm, with unit cell parameters a = 8.001(1) Å, b = 11.696 (2) Å, c = 15.020(3) Å (Z = 4; R 1 = 0.0234). The structure features germanium-centered neodymium clusters Ge@Nd 9 which share faces to form layers separated by zigzag chains of cobalt atoms capped by carbon. Density of states calculations confirm that this compound is metallic, and indicate that the cobalt should not have a magnetic moment. This is supported by magnetic susceptibility measurements which show a low temperature ferromagnetic ordering at T C = 50 K due to the Nd 3+ ions. Magnetization field dependence studies on single crystals indicate this compound is a strong ferromagnet with large anisotropy; the Nd 3+ magnetic moments align along the a-axis.

Cerium cobalt borocarbide grown from Ce/Co eutectic flux has a partially disordered structure containing cobalt squares capped with borocarbide chains.