Experimental method to determine specific heat and transition enthalpy at a first order phase transition: fundamentals and application to a NiMnIn Heusler alloy

TL;DR

This paper introduces a novel calorimetric method to measure specific heat and transition enthalpy during first-order phase transitions, demonstrating its effectiveness on a NiMnIn Heusler alloy with consistent results independent of experimental parameters.

Contribution

The paper presents a new experimental technique for accurately determining specific heat and enthalpy during first-order phase transitions, overcoming limitations of existing methods.

Findings

The method accurately measures specific heat during phase transitions.

It provides enthalpy excess analysis through energy balance.

Results are independent of pulse rate and amplitude.

Abstract

A new method that characterizes thermal properties during a first-order phase transition is described. The technique consists in exciting the sample by a series of constant frequency thermal pulses which one in every N pulses (N is a small number like four) being exceedingly large in amplitude. This pulse induces phase transformation which is inhibited during the following smaller pulses due to thermal hysteresis. That way the specific heat for a given mixture of phases can be determined. The results obtained are independent of experimental parameters like the rate and the amplitude of the pulses, unlike what happens in other calorimetric techniques. The method also provides the enthalpy excess by analyzing the energy balance between the dissipated heat and the heat flowing during each pulse of measurement. The protocol is tested to analyze the phase transitions of a Heusler alloy Ni 50.54 Mn 33.65 In 15.82 . The paramagnetic-ferromagnetic transition for the austenite phase is continuous and the specific heat shows a lambda anomaly. The martensitic phase transition shows a first-order character and the specific heat follows a step-like behaviour in contrast with previously reported large-peak anomalies.