Effect of high-pressure on the charge density wave and antiferromagnetic transitions in GdNiC2 and NdNiC2

The paper presents the effect of high-pressure (HP) on the charge-density-wave (CDW) and antiferromagnetic (AFM) phases in rare-earth intermetallic compounds GdNiC 2 and NdNiC 2 . Synchrotron powder x-ray diffraction up to ~ 9 GPa in both the systems revealed that under HP the crystal symmetry remained the same (CeNiC 2 -type orthorhombic, space group Amm 2, # 38). With increasing pressure, there was a gradual decrease in lattice parameters, with a weak, but clear anisotropy, however, the unit-cell volume followed a smooth second order Birch-Murnaghan equation of state. In both the systems electrical resistivity measurements in the temperature range 260 to 2 K were undertaken up to ~ 3 GPa. Under HP, in GdNiC 2 , the CDW transition temperature decreases from ~190.6 K at ambient pressure to ~184.5 K at 3.2 GPa. The anomaly related to the AFM transition also shifts to lower temperatures with increasing pressure, however with a qualitative change, indicative of a change in the order of transition from first to second above 2 GPa. Similar to GdNiC 2 , with HP, the both the CDW and AFM transition temperatures decreases also in NdNiC 2 . In particular, at 3.0 GPa, the CDW and AFM decreases respectively to ~101.4 from 106.5 K and to ~13.6 from 16.8 K. Density-functional theory simulations of GdNiC 2 and NdNiC 2 revealed a progressive decrease in lattice parameters in the 0-10 GPa pressure range, where the local magnetic moments are found to remain robust. This together with the experimental results indicate a close connection of the crystal structure to the magnetic ground state. • High-pressure resistivity of GdNiC 2 and NdNiC 2 up to ~3 GPa. • CDW and AFM transitions show a pressure dependence. • Compounds retains their orthorhombic structure up to ~9 GPa . • There is an anisotropic lattice compression under pressure.