Ultrasonic studies of the magnetic phase transition in MnSi

TL;DR

This study investigates the magnetic phase transition in MnSi using ultrasonic measurements, revealing elastic constant softening and emphasizing that the transition is a minor feature within a broader thermodynamic transformation.

Contribution

It provides detailed ultrasonic evidence showing the magnetic transition in MnSi is a subtle feature amid a larger phase transformation, highlighting the behavior of elastic constants near the transition.

Findings

Significant softening of longitudinal elastic constants at ~29.6 K

Small discontinuities at ~28.8 K indicating magnetic transition

Shear elastic moduli show no softening, only volume effects

Abstract

Measurements of the sound velocities in a single crystal of MnSi were performed in the temperature range 4-150 K. Elastic constants, controlling propagation of longitudinal waves reveal significant softening at a temperature of about 29.6 K and small discontinuities at $\sim$28.8 K, which corresponds to the magnetic phase transition in MnSi. In contrast the shear elastic moduli do not show any softening at all, reacting only to the small volume deformation caused by the magneto-volume effect. The current ultrasonic study exposes an important fact that the magnetic phase transition in MnSi, occurring at 28.8 K, is just a minor feature of the global transformation marked by the rounded maxima or minima of heat capacity, thermal expansion coefficient, sound velocities and absorption, and the temperature derivative of resistivity.