On the nature of the phase transition in the itinerant helimagnet MnSi

TL;DR

This study investigates the phase transition in MnSi, revealing it is weakly first order at ambient pressure and likely second order at high pressure, challenging existing phase diagram assumptions.

Contribution

It provides detailed thermodynamic and transport measurements indicating the nature of the phase transition in MnSi and its pressure dependence.

Findings

Transition is weakly first order at ambient pressure.

Transition becomes second order at high pressure.

Experimental data challenge existing phase diagram models.

Abstract

A careful study of thermodynamic and transport properties of a high quality single crystal of MnSi at ambient pressure suggests that its transition to a helical magnetic state near 29 K is weakly first order. The heat capacity, temperature derivatives of resistivity, thermal expansion and magnetic susceptibility exhibit a specific structure around the phase transition point, interpreted as a combination of first and second order features. Conclusions drawn from these experiments question prevailing views on the phase diagram of MnSi and propose that the phase transition under study becomes second order at high pressure and low temperature.