Pressure Collapse of the Magnetic Ordering in MnSi via Thermal Expansion

TL;DR

This study investigates the pressure-induced first order magnetic phase transition in MnSi through thermal expansion measurements, revealing a volume discontinuity and insights into magnetic interactions near the critical pressure.

Contribution

It provides detailed thermodynamic analysis of the pressure-driven magnetic transition in MnSi, confirming its first order nature and examining the behavior of magnetic interactions.

Findings

Volume discontinuity at Pc ~1.6 GPa confirms first order transition.

Enhanced Sommerfeld coefficient below Pc indicates increased electronic correlations.

Weak pressure dependence of characteristic magnetic fields suggests stable magnetic interaction strengths.

Abstract

The itinerant quasi-ferromagnetic metal MnSi has been studied by detailed thermal expansion measurements under pressures and magnetic fields. A sudden decrease of the volume at the critical pressure Pc ~1.6 GPa has been observed and is in good agreement with the pressure variation of the volume fraction of the spiral magnetic ordering. This confirms that the magnetic order disappears by a first order phase transition. The energy change estimated by the volume discontinuity on crossing Pc is of similar order as the Zeeman energy of the transition from the spiral ground state to a polarized paramagnetic one under magnetic field. In contrast to the strong pressure dependence of the transition temperature, the characteristic fields are weakly pressure dependent, indicating that the strength of the ferromagnetic and the Dzyaloshinskii-Moriya interactions do not change drastically around Pc. The evaluated results of the thermal expansion coefficient and the magnetostriction are analyzed thermodynamically. The Sommerfeld coefficient of the linear temperature term of the specific heat is enhanced just below Pc. The magnetic field-temperature phase diagrams in the ordered and paramagnetic phases are also compared. Comparison is made with other heavy fermion compounds with first order phase transition at 0 K.