Importance of Thermal Disorder on the Properties of Alloys: Origin of Paramagnetism and Structural Anomalies in Iron-Aluminum

TL;DR

This paper investigates how thermal disorder influences the magnetic and structural properties of iron-aluminum alloys, revealing the origins of paramagnetism and lattice anomalies through advanced theoretical analysis.

Contribution

It demonstrates that thermal and chemical disorder induce paramagnetism and structural anomalies in Fe-Al alloys, challenging previous theoretical models and explaining experimental observations.

Findings

Thermal disorder causes paramagnetism with local moments in FeAl.

Chemical disorder explains lattice constant anomalies in Fe-Al alloys.

Theoretical analysis aligns with experimental magnetic and structural data.

Abstract

The bcc-based Fe_{1-x}Al_{x} exhibit interesting magnetic and anomalous structural properties as a function of composition and sample processing conditions arising from thermal or off-stoichiometric chemical disorder, and, although well studied, these properties are not understood. In stoichiometric B2 FeAl, including the effects of partial long-range order (i.e., thermal antisites), we find the observed paramagnetic response (with non-zero local moments), in contrast to past investigations which find ferromagnetism based on local density approximation (LDA) to density functional theory or which find a non-magnetic state from LDA+U, both of which are inconsistent with experiment. Moreover, from this magneto-chemical coupling, we are able to determine the origins of the lattice constant anomalies found in Fe_{1-x}Al_{x} for x=25-50, as observed from various processing conditions.