Effect of Carbon Insertion on the Structural and Magnetic Properties of NdScSi

The investigation of layered intermetallic compounds containing light elements like hydrogen has great potential for superconductivity. We studied the insertion of carbon atoms in CeScSi-type intermetallics (an ordered variant of the La₂Sb structure type), and here, we report the new carbide NdScSiC_0.5. Carbon insertion keeps the pristine compound's space group, I4/mmm, but causes an anisotropic expansion of the unit cell with an increase in the a parameter and a decrease of the c parameter. X-ray and neutron diffraction measurements indicate the existence of a NdScSiC solid solution (0.2 < x ≤ 0.5) with carbon atoms occupying only the Sc₄Nd₂ octahedral sites while leaving the Nd₄ tetrahedral sites vacant. Magnetization measurements unveil a linear reduction of the ferromagnetic ordering temperature from T_C = ∼171 K to ∼50 K with increasing carbon content. The ferromagnetic structures of the pristine NdScSi and the filled NdScSiC_0.5 have been determined from neutron diffraction measurements. Finally, we discuss the effect of carbon versus hydrogen insertion on electronic and magnetic properties based on density functional theory calculations. Although the unpaired spin density channels between Nd and Sc atoms (responsible of the high Curie temperature in NdScSi) are reduced upon carbon insertion, the strong Nd-C interaction, linked to a reduced c lattice parameter in NdScSiC_0.5, ensures a strong magnetic coupling between the Nd double layer along the c axis and the ferromagnetic order is preserved.