Magnetic and electrical properties of LaC2, CeC2, PrC2, NdC2, and SmC2

The electrical resistivities of the tetragonal CaC2-type rare-earth dicarbides RC2 (R = La, Ce, Pr, Nd, and Sm) and the magnetic susceptibilities of RC2 (R = Pr, Nd, and Sm) are reported. The dicarbide LaC2 becomes a superconductor at 1.6 K, which is in good agreement with literature values. The resistivity vs temperature curve of CeC2 indicates a small hump at 30 K, and those of PrC2 and NdC2 show a sharp change in slope at 18 and 25 K, respectively, all verifying the antiferromagnetic transitions found by neutron diffraction. The temperature dependence of resistivity of CeC2 was explained on the basis of the Γ7 components of Ce3+. The compound PrC2 becomes ferromagnetic at a zero-field Curie temperature of 7 K. This magnetic behavior differs significantly from that reported previously, suggesting an antiferromagnetic-to-ferromagnetic transition in the field of less than 700 Oe. The susceptibility of NdC2 shows a field-independent antiferromagnetic transition at 24 K. An antiferromagnetic transition in SmC2 was found anew at 21 K in both the resistivity and susceptibility data, exhibiting Van Vleck’s Sm3+ characteristics. The Sm3+ ion in SmC2 appears to be largely confined in the J = 5/2 ground state at about 21 K, since the paramagnetic Curie temperature reduced thereby and those of the other dicarbides can be correlated reasonably in the de Gennes factor plot.