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Crystal and magnetic structure of the superconductor CeNi$_{0.8}$Bi$_2$

We have performed powder neutron diffraction on the new superconductor, CeNi$_{0.8}$Bi$_2$ with a superconducting transtion temperature $T_\textrm{c} \sim$ 4.2 K. The structural parameters of this compound at room temperature are determined by Rietveld analysis. Below about 5 K, the clear magnetic Bragg peaks with propagation vector $q$=(0 0 0) are observed. The observed intensities of magnetic Bragg peaks can be explained by the magnetic structure that the two Ce moments in the unit cell are antiparallel along c axis. The magnetic Bragg peaks are observed in the superconducting state, indicating the coexistence of the antiferromagnetic ordering and the superconductivity in this compound. The intensity of magnetic Bragg peak monotonously increases with decreasing temperature below $T_\textrm{N}$ and does not exhibit apparent anomaly at $T_\textrm{c}$, obviously different from cases of heavy fermion superconductors in which the magnetic ordering and the superconductivity coexist, for example, Cd-doped CeCoIn$_5$. These results suggest that the 4$f$ electron of the Ce atom is not coupled with the superconducting carrier, and the magnetic ordering is almost independent of the superconductivity in CeNi$_{0.8}$Bi$_2$.