We report a comprehensive study of ${\mathrm{CeIn}}_{3-x}{\mathrm{Sn}}_x$ ($0.55\le x\le 0.8$) single crystals close to the antiferromagnetic quantum-critical point (QCP) at $x_c\approx 0.67$ by means of the low-temperature thermal expansion and Grüneisen parameter. This system represents the first example for a cubic heavy fermion in which $T_N$ can be suppressed continuously down to $T=0$. A characteristic sign change of the Grüneisen parameter between the antiferromagnetic and paramagnetic states indicates the accumulation of entropy close to the QCP. The observed quantum-critical behavior is compatible with the predictions of the itinerant theory for three-dimensional critical spin fluctuations. This has important implications for the role of the dimensionality in heavy-fermion QCPs.

• Received 1 February 2006

DOI:https://doi.org/10.1103/PhysRevLett.96.256403