On the phase diagram of the itinerant helimagnet MnSi: does MnSi become quantum critical ?

TL;DR

This study investigates the pressure-induced evolution of the magnetic phase transition in MnSi, suggesting the suppression of first order features and the potential emergence of quantum critical behavior at high pressures.

Contribution

It provides experimental evidence that the first order transition in MnSi diminishes under high pressure, supporting the possibility of quantum criticality in this material.

Findings

First order transition features weaken with pressure

No strong first order transition at high pressures

Potential for quantum critical phenomena in MnSi

Abstract

We performed a series of resistivity measurements of a MnSi single crystal at high pressures, created by a piston-cylinder device with a liquid pressure medium. The form of the resistivity curve at ambient pressure clearly indicates a first order nature of the magnetic phase transition in MnSi. Application of high pressure shows fast degradation of the first order features of the phase transition. The temperature derivative of resistivity demonstrates two notable features of the phase transition that disappear on pressure increasing. They are a sharp peak marking the first order phase transition and a shallow maximum, situated slightly above the critical temperature and pointing to the domain of prominent helical fluctuations. The current experimental data rule out any strong first order phase transition in MnSi at high pressures and low temperatures, which would prevent development of a quantum critical region. On the contrary, there should exist true quantum critical phenomena in MnSi at high pressures because a tiny first order transition, if it survives at high pressures to the lowest temperature, hardly could suppress the entire quantum critical region.