Evolution of quantum criticality in the system CeNi9Ge4

TL;DR

This paper investigates the evolution of quantum criticality in CeNi9Ge4, a heavy fermion system, by tuning its composition and studying its magnetic and electronic properties to understand the transition from non-Fermi liquid to magnetic order.

Contribution

It provides detailed experimental insights into how small compositional changes induce magnetic order and explores the connection to quantum critical points in heavy fermion systems.

Findings

CeNi9Ge4 has record specific heat coefficient and unique magnetic properties.

Replacing Ni with Cu or Co induces magnetic order at low temperatures.

Experimental evidence suggests a transition from non-Fermi liquid to magnetic order related to quantum criticality.

Abstract

The heavy fermion system CeNi9Ge4 exhibits a paramagnetic ground state with remarkable features such as: a record value of the electronic specific heat coefficient in systems with a paramagnetic ground state, \gamma = C/T \simeq 5.5 J/molK^2 at 80 mK, a temperature-dependent Sommerfeld-Wilson ratio, R=\chi/\gamma, below 1 K and an approximate single ion scaling of the 4f-magnetic specific heat and susceptibility. These features are related to a rather small Kondo energy scale of a few Kelvin in combination with a quasi-quartet crystal field ground state. Tuning the system towards long range magnetic order is accomplished by replacing a few at.% of Ni by Cu or Co. Specific heat, susceptibility and resistivity studies reveal T_N \sim 0.2 K for CeNi8CuGe4 and T_N \sim 1 K for CeNi8CoGe4. To gain insight whether the transition from the paramagnetic NFL state to the magnetically ordered ground state is connected with a heavy fermion quantum critical point we performed specific heat and ac susceptibility studies and utilized the \mu SR technique and quasi-elastic neutron scattering.