Magneto-structural correlations in a systematically disordered B2 lattice

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.

6 pages, 3 figures