Ab-initio based analytical evaluation of entropy in magnetocaloric materials with first order phase transitions

TL;DR

This paper integrates ab-initio calculations with thermodynamic models to analyze entropy contributions in magnetocaloric materials with first order phase transitions, providing insights into transition behavior and experimental validation.

Contribution

It introduces a combined theoretical approach to evaluate electronic and spin entropy effects on phase transitions in magnetocaloric materials.

Findings

Electronic entropy induces first order phase transitions.

Localized spin entropy lowers transition temperatures.

Model predictions align with experimental data.

Abstract

We combine spin polarised density functional theory and thermodynamic mean field theory to describe the phase transitions of antiperovskite manganese nitrides. We find that the inclusion of the localized spin contribution to the entropy, evaluated through mean field theory, lowers the transition temperatures. Furthermore, we show that the electronic entropy leads to first order phase transitions in agreement with experiments whereas the localized spin contribution adds second order character to the transition. We compare our predictions to available experimental data to assess the validity of the assumptions underpinning our multilevel modelling.