Development of the heavy-fermion state inCe2IrIn8and the effects of Ce dilution in(Ce1−xLax)2IrIn8

Abstract

We report a study of muon Knight shifts to investigate the formation of the heavy-fermion state in single crystals of ${({\text{Ce}}_{1\ensuremath{-}x}{\text{La}}_{x})}_{2}{\text{IrIn}}_{8}$. Two different kinds of Knight-shift anomalies (deviations from a linear relation between the Knight shift and the susceptibility) are found: (1) a high-temperature effect arising from depopulation of crystalline electric field levels with temperature, and (2) a lower-temperature anomaly arising from the onset of the heavy-fermion state below a characteristic temperature ${T}^{\ensuremath{\ast}}$, in agreement with the ``two-fluid'' model of heavy-fermion formation. In ${\text{Ce}}_{2}{\text{IrIn}}_{8}$, we find ${T}_{c}^{\ensuremath{\ast}}=20.0(6)\text{ }\text{K}$ and ${T}_{a}^{\ensuremath{\ast}}=15.2(1.2)\text{ }\text{K}$ for applied field $H\ensuremath{\parallel}c$ axis and $H\ensuremath{\parallel}a$ axis, respectively. For the Ce diluted systems ${({\text{Ce}}_{1\ensuremath{-}x}{\text{La}}_{x})}_{2}{\text{IrIn}}_{8}$, $x=0.1$, 0.25, 0.50, 0.70, and 0.90, ${T}^{\ensuremath{\ast}}$ decreases linearly for $x\ensuremath{\le}0.5$, reaching zero near $x=0.7$, indicating the reduction in intersite $f$-spin correlations with Ce dilution. A comparison with nuclear magnetic-resonance measurements of Knight-shift anomalies in several other heavy-fermion compounds suggests that the observed small anisotropy in ${T}^{\ensuremath{\ast}}$ may be induced by the applied field, and that ${T}^{\ensuremath{\ast}}$ may be inherently isotropic, even in highly anisotropic materials.