Magneto-structural correlations in a systematically disordered B2 lattice

TL;DR

This study systematically disordered B2 Fe$_{60}$Al$_{40}$ thin films to explore how atomic disorder affects magnetic properties, revealing a critical point where saturation magnetization sharply increases, guided by both experimental and DFT insights.

Contribution

It provides a detailed correlation between atomic disorder, lattice parameter, and magnetization in B2 Fe$_{60}$Al$_{40}$ alloys, highlighting a critical disorder level for magnetic tuning.

Findings

Critical disorder point at 1-S=0.6 and a0=291 pm with sharp magnetization increase

Disordering increases lattice parameter by approximately 1%

DFT suggests different magnetic behaviors below and above the critical point

Abstract

Ferromagnetism in certain B2 ordered alloys such as Fe$_{60}$Al$_{40}$ can be switched on, and tuned, via antisite disordering of the atomic arrangement. The disordering is accompanied by a $\sim$1 % increase in the lattice parameter. Here we performed a systematic disordering of B2 Fe$_{60}$Al$_{40}$ thin films, and obtained correlations between the order parameter ($S$), lattice parameter ($a_0$), and the induced saturation magnetization ($M_{s}$). As the lattice is gradually disordered, a critical point occurs at 1-$S$=0.6 and $a_0$=291 pm, where a sharp increase of the $M_{s}$ is observed. DFT calculations suggest that below the critical point the system magnetically behaves as it would still be fully ordered, whereas above, it is largely the increase of $a_0$ in the disordered state that determines the $M_{s}$. The insights obtained here can be useful for achieving tailored magnetic properties in alloys through disordering.