B2 disorder-driven magnetic properties of hydrothermally synthesized Fe–Co–Al full Heusler alloys: a combined theoretical and experimental study on bulk and disordered nanoparticles

Abstract

A series of Fe_2−xCo_1+xAl full Heusler alloy nanoparticles were successfully prepared using a controlled hydrothermal technique with particle sizes ranging between 16 and 35 nm. First-principles DFT calculations were also performed to predict the electronic structures, magnetic moments, and phase stability across various compositions. The structure and morphology of the nanoparticles were studied using X-rays and the electron diffraction technique, which validated the presence of chemical disorder of B2 type in the prepared alloys. The structural and magnetic properties of the alloys with varied Fe/Co ratios were studied with optimized pH and a reducing agent. The experimentally obtained moments are found to be larger than the predicted L2₁-based Slater–Pauling values of 4.0µ_B f.u.⁻¹ and 5.00µ_B f.u.⁻¹ for Fe₂CoAl and Co₂FeAl respectively. The primary factor influencing the magnetic behavior of the alloy system has been attributed to the presence of secondary phases and the chemical disorder. This work provides a simple hydrothermal synthesis method to prepare B2 disordered full Heusler alloy nanoparticles and shows that compositional control is a viable approach towards improving saturation magnetization and other magnetic parameters in these promising materials for spintronic applications.