Approaching quantum criticality in a partially geometrically frustrated heavy-fermion metal

Abstract

In the antiferromagnetic (AF) heavy-fermion system CePdAl the magnetic Ce ions form a network of equilateral triangles in the $(001)$ plane, similar to the kagom\'e lattice, with one third of the Ce moments not participating in the long-range order. The N\'eel temperature ${T}_{\mathrm{N}}=2.7\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ is reduced upon replacing Pd by Ni in ${\text{CePd}}_{1\ensuremath{-}x}{\text{Ni}}_{x}\text{Al}$, with ${T}_{\mathrm{N}}\ensuremath{\rightarrow}0$ for $x=0.144$, where the specific heat $C$ exhibits a $C/T\ensuremath{\propto}\ensuremath{-}log\phantom{\rule{0.28em}{0ex}}T$ dependence. Within the Hertz-Millis-Moriya model of quantum criticality, this behavior might indicate 2D critical antiferromagnetic fluctuations arising from the decoupling of 3D magnetic order by frustration. On the other hand, the simultaneous presence of Kondo effect and geometric frustration might entail a different route to quantum criticality.