Finite-temperature magnetism in bcc Fe under compression

TL;DR

This study models finite-temperature magnetic fluctuations in bcc Fe under pressure, revealing their significant impact on thermodynamic properties and improving agreement with experimental thermal expansion data.

Contribution

It introduces a combined approach using a tight-binding model, Heisenberg Hamiltonian, and Monte Carlo simulations to analyze finite-temperature magnetism in bcc Fe.

Findings

Finite-temperature magnetism affects thermodynamic properties.

Including magnetic fluctuations improves thermal expansion predictions.

The model accurately predicts Curie temperature and heat capacity.

Abstract

We investigate the contributions of finite-temperature magnetic fluctuations to the thermodynamic properties of bcc Fe as a function of pressure. First, we apply a tight-binding total-energy model parameterized to first-principles linearized augmented planewave computations to examine various ferromagnetic, anti-ferromagnetic, and noncollinear spin spiral states at zero temperature. The tight-binding data are fit to a generalized Heisenberg Hamiltonian to describe the magnetic energy functional based on local moments. We then use Monte Carlo simulations to compute the magnetic susceptibility, the Curie temperature, heat capacity, and magnetic free energy. Including the finite-temperature magnetism improves the agreement with experiment for the calculated thermal expansion coefficients.