History dependent nucleation and growth of the martensitic phase in a magnetic shape memory alloy Ni$_{45}$Co$_{5}$Mn$_{38}$Sn$_{12}$

TL;DR

This study investigates how the history of magnetic field and temperature changes influences the nucleation and growth of martensitic phases in a Ni-Co-Mn-Sn shape memory alloy, revealing path-dependent kinetics and relaxation behaviors.

Contribution

It demonstrates the history-dependent nucleation and growth dynamics of martensitic phases, highlighting the role of thermomagnetic paths in phase transformation kinetics.

Findings

Relaxation rates depend on non-equilibrium phase fraction.

Long-term relaxation is weakly dependent on temperature.

Path-dependent critical radii influence nucleation and growth.

Abstract

We study through the time evolution of magnetization the low temperature (T) dynamics of the metastable coexisting phases created by traversing different paths in magnetic field (H) and T space in a shape memory alloy system, Ni$_{45}$Co$_{5}$Mn$_{38}$Sn$_{12}$. It is shown that these coexisting phases consisting of a fraction of kinetically arrested austenite phase and remaining fraction of low-T equilibrium martensitic phase undergo a slow relaxation to low magnetization (martensitic) state but with very different thermomagnetic history-dependent rates at the same T and H. We discovered that, when the nucleation of martensitic phase is initiated at much lower T through the de-arrest of the glass like arrested state contrasted with the respective first order transformation (through supercooling at much higher T), then the long time relaxation rate scales with the non-equilibrium phase fraction but has a very weak dependence on T. This is explained on the basis of the H-T path dependent size of the critical radii of the nuclei and the subsequent growth of the equilibrium phase through the motion of the interface.