Antiferromagnetic correlations in a valence fluctuating kagome lattice CeIrSn

Ce/Yb-based intermetallic compounds with a large Kondo temperature $T_K$ exceeding 100 K are known to show a non-magnetic Fermi liquid ground state. The equiatomic compounds Ce$T$Sn ($T$ = Rh, Ir) where Ce ions form a quasi-kagome lattice have $T_K$ ~ 240 K (Rh) and 480 K (Ir) [1]. These huge $T_K$s indicate CeTSn are a valence fluctuating materials as we confirmed by hard X-ray photoelectron spectroscopy. Despite the strong valence fluctuation, Ce$T$Sn exhibit non-Fermi liquid behaviors below 2 K, implying magnetic instabilities [2,3].
Such Ce-based valence fluctuating materials are expected to show positive thermal expansion coefficient $\alpha $ and magnetostriction one $\lambda$. However, in CeIrSn, we observed negative $\alpha$ and $\lambda$ below $T$* ~ 2 K [4]. The negative sign in $\lambda$ changes to positive by crossing metamagnetism at 6 T as shown in the figure. These characters in $\alpha$ and $\lambda$ are resemble to those in Ce-based antiferromagnets in spite of the absence of the magnetic long-range order. Indeed, muon spin relaxation measurements revealed the internal field by the magnetic correlations below $T$*. Our studies clarify the development of the hidden magnetic correlations deep inside the non-magnetic-like valence fluctuating state in CeIrSn with $T_K$ ~ 480 K.

[1] Y. Bando et al., J. Alloys Compd. 313, 1 (2000).
[2] Y. Tokiwa et al., Sci. Adv. 1, e1500001 (2015).
[3] S. Tsuda, C.L. Yang, Y. Shimura et al., Phys. Rev. B 98, 155147 (2018).
[4] Y. Shimura, A. Wörl, M. Sundermann et al., Phys. Rev. Lett. 126, 217202 (2021).