What is the speed limit of martensitic transformations?

TL;DR

This study demonstrates that martensitic transformations can occur in under ten nanoseconds, revealing a fundamental speed limit linked to energy requirements, with implications for fast-actuation and energy applications.

Contribution

It is the first to experimentally determine the nanosecond-scale speed limit of martensitic transformations and relate it to fundamental physical constraints.

Findings

Transformation completed in under ten nanoseconds.

Speed limit is approximately 2.5 x 10^{27} (Js)^{-1} per unit cell.

Transformation speed is driven by thermal energy and is comparable to limits in microelectronics.

Abstract

Structural martensitic transformations enable various applications, which range from high stroke actuation and sensing to energy efficient magnetocaloric refrigeration and thermomagnetic energy harvesting. All these emerging applications benefit from a fast transformation, but up to now the speed limit of martensitic transformations has not been explored. Here, we demonstrate that a martensite to austenite transformation can be completed in under ten nanoseconds. We heat an epitaxial Ni-Mn-Ga film with a laser pulse and use synchrotron diffraction to probe the influence of initial sample temperature and overheating on transformation rate and ratio. We demonstrate that an increase of thermal energy drives this transformation faster. Though the observed speed limit of 2.5 x 10^{27} (Js)^{-1} per unit cell leaves plenty of room for a further acceleration of applications, our analysis reveals that the practical limit will be the energy required for switching. Our experiments unveil that martensitic transformations obey similar speed limits as in microelectronics, which are expressed by the Margolus-Levitin theorem.