# Thermal memory fading by heating to a lower temperature: experimental data on polycrystalline NiFeGa ribbons and 2D statistical model predictions

## TL;DR

This study investigates a novel thermal memory fading effect in NiFeGa ribbons, showing that heating to a lower temperature can diminish previously recorded memory dips, supported by experimental data and a 2D statistical model.

## Contribution

It reports the first observation of memory fading by heating to lower temperatures in polycrystalline NiFeGa ribbons and provides a statistical model explaining this phenomenon.

## Key findings

- Memory dips decrease or vanish when reheated to lower temperatures.
- Fading effect is more pronounced with smaller temperature differences.
- A 2D statistical model supports the experimental observations.

## Abstract

Shape memory alloys are known to memorise one -or several- temperatures at which the martensite-austenite transformation was stopped before completion in the past, the memory manifesting as specific dips in subsequent calorimetric scans. Previous studies have shown that this memory can be erased by heating to higher temperatures than the ones previously recorded. In this paper, we study a distinct memory fading effect which takes place by heating to a lower temperature. This effect is reported in NiFeGa as polycrystalline ribbons, the alloy being initially studied as bulk for which the thermal memory effect was not found. If, after an initial incomplete heating up to T1 one performs a second incomplete heating up to T2<T1, a new calorimetric dip appears at T2, as expected, while less expected was that the dip corresponding to T1 reduces in amplitude or even vanishes (if the arrest at T2 is repeated). The memory fading effect is more clear for small differences T1-T2 and less obvious or absent for large ones. The second part of the paper employs a statistical 2D model, which associates the memorized temperatures with a depletion of certain martensite plates sizes, and also supports the memory fading effect.