Pressure dependence of the spin structure in a pressure-induced superconductor CeNiC₂

CeNiC₂, which shows a heavy fermion behavior, exhibits successive magnetic transitions from paramagnetic phase to an incommensurate antiferromagnetic phase to a collinear antiferromagnetic phase with decreasing temperature at ambient pressure. With applied pressure, the magnetic transition temperatures first increase and then decrease above ~7 GPa and superconductivity appears around 11 GPa, where the magnetic order is almost suppressed, with the highest superconducting transition temperature of 3.7 K [1]. It is important to clarify the coupling between the magnetism and the superconducting pairing mechanism. However, the detailed magnetic structure as a function of pressure has not been reported so far. In order to elucidate the magnetic ground state adjacent to the superconducting phase, high-pressure neutron diffraction measurements have been performed up to 4 GPa using single crystals, which have become available recently [2]. We found that the collinear antiferromagnetic phase disappears below 1 GPa and the incommensurate phase becomes the ground state. We will report detailed magnetic structures as a function of pressure.

[1] S. Katano et al., Phys. Rev. B 99, 100501 (2019); [2] H. Ma et al., Phys. Rev. B 108, 064435 (2023).