CeIr${}_3$Ge${}_7$: a local moment antiferromagnetic metal with extremely low ordering temperature

Abstract

CeIr${}_3$Ge${}_7$ is an antiferromagnetic metal with a remarkably low ordering temperature $T_{\mathrm{N}}$ = 0.63 K, while most Ce-based magnets order between 2 and 15 K. Thermodynamic and transport properties as a function of magnetic field or pressure do not show signatures of Kondo correlations, interaction competition, or frustration, as had been observed in a few antiferromagnets with comparably low or lower $T_{\mathrm{N}}$. The averaged Weiss temperature measured below 10 K is comparable to $T_{\mathrm{N}}$ suggesting that the RKKY exchange coupling is very weak in this material. The unusually low $T_{\mathrm{N}}$ in CeIr${}_3$Ge${}_7$ can therefore be attributed to the large Ce-Ce bond length of about 5.7 Å, which is about 1.5 Å larger than in the most Ce-based intermetallic systems.

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