Pressure Effects on CeMnSi: Evolution of Ce 4f and Mn 3d Electronic States and Negative Thermal Expansion

TL;DR

This study explores how pressure influences the magnetic and electronic states of CeMnSi, revealing suppression of Mn antiferromagnetism, emergence of new anomalies, and negative thermal expansion linked to heavy-fermion behavior.

Contribution

It provides new insights into pressure-induced magnetic and electronic state transitions in CeMnSi, including the suppression of Mn order and the relation to heavy-fermion properties.

Findings

Mn antiferromagnetic order disappears at ~1.3 GPa

A pressure-induced anomaly appears at ~97 K and shifts higher with pressure

Negative thermal expansion observed below 40 K at ambient pressure

Abstract

We investigated pressure effects on the nontrivial heavy-fermion antiferromagnet CeMnSi by means of electrical resistivity and powder X-ray diffraction. With increasing pressure, the antiferromagnetic order of Mn (T_N ~ 240 K at ambient pressure) is rapidly suppressed and disappears at P_c ~ 1.3 GPa. Instead, a pressure-induced anomaly appears at T_M ~ 97 K and shifts to higher temperatures with increasing pressure. The switching of the Mn magnetic state may reflect a modification of the magnetic symmetry of the system, which could influence the stability of the heavy-fermion state. In the low-pressure region, non-Fermi-liquid-like behavior characterized by nearly T-linear resistivity is observed around 0.7 GPa. In addition, the resistivity shows a marked reduction below T_M and a qualitative change toward more metallic behavior above the structural transition pressure P_s ~ 5.7 GPa. At ambient pressure, CeMnSi exhibits negative thermal expansion below ~40 K, which is absent in LaMnSi, supporting the formation of a heavy-fermion ground state.