Magnetochemical effects on phase stability and vacancy formation in fcc Fe-Ni alloys

TL;DR

This study uses advanced computational models to analyze how magnetochemical interactions influence phase stability and vacancy formation in fcc Fe-Ni alloys, successfully predicting phase transitions and revealing magnetic effects on vacancies.

Contribution

It introduces a density functional theory-based model that explicitly includes spin and chemical variables to predict phase behavior and vacancy formation in Fe-Ni alloys.

Findings

Predicted composition-dependent Curie and order-disorder transition temperatures.

Identified magnetically driven phase separation around 10-40% Ni at 570-700 K.

Found magnetic effects significantly influence vacancy formation, especially in concentrated alloys.

Abstract

We investigate phase stability and vacancy formation in fcc Fe-Ni alloys over a broad composition-temperature range, via a density functional theory parametrized effective interaction model, which includes explicitly spin and chemical variables. On-lattice Monte Carlo simulations based on this model are used to predict the temperature evolution of the magnetochemical phase. The experimental composition-dependent Curie and chemical order-disorder transition temperatures are successfully predicted. We point out a significant effect of chemical and magnetic orders on the magnetic and chemical transitions, respectively. The resulting phase diagram shows a magnetically driven phase separation around 10-40% Ni and 570-700 K, between ferromagnetic and paramagnetic solid solutions, in agreement with experimental observations. We compute vacancy formation magnetic free energy as a function of temperature and alloy composition. We identify opposite magnetic and chemical disordering effects on vacancy formation in the alloys with 50% and 75% Ni. We find that thermal magnetic effects on vacancy formation are much larger in concentrated Fe-Ni alloys than in fcc Fe and Ni due to a stronger magnetic interaction.