The unusual phase diagram of CeNiGe2

TL;DR

This study explores the complex pressure-induced phase transitions in the heavy fermion antiferromagnet CeNiGe2, revealing an unusual phase diagram that deviates from traditional models and shows multiple magnetic transitions.

Contribution

It provides the first detailed pressure-temperature phase diagram of CeNiGe2, uncovering novel transitions and challenging existing theoretical frameworks for heavy fermion systems.

Findings

Magnetic transitions at 0.1 GPa are replaced by a single transition at 0.7 GPa.

A new transition appears around 1.7 GPa with signs of first order character.

The phase diagram significantly differs from the Doniach model.

Abstract

The heavy fermion antiferromagnet CeNiGe2 was investigated under pressure by resistivity and ac calorimetry up to 4 GPa and down to 40 mK. The two magnetic transitions found in both resistivity and specific heat at 0.1 GPa at T_N1=3.95 and T_{N2}=3.21 K are replaced by a single one at 0.7 GPa and 2.81 K. Increasing pressure initially reduces this further, however at about 1.7 GPa a new transition appears, accompanied by a marked change in the pressure dependence of the ordering temperatures, the temperature dependence of the resistivity, and the residual resistivity. There are signs that this new transition has some first order character. The phase diagram of CeNiGe2 bears little resemblance to the Doniach phase diagram widely used to classify heavy fermion compounds.