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.
Categories: cond-mat.mtrl-sci