Magneto-structural correlations in a systematically disordered B2 lattice

Ferromagnetism in certain B2 ordered alloys such as Fe60Al40 can be switched on, and tuned, via antisite disordering of the atomic arrangement. The disordering is accompanied by a 1% increase in the lattice parameter. Here we performed a systematic disordering of B2 Fe60Al40 thin lms, and obtained correlations between the order parameter (S), lattice parameter (a0), and the induced saturation magnetization (Ms). As the lattice is gradually disordered, a critical point occurs at 1-S=0.6 and a0=2.91A, where a sharp increase of the Ms 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 a0 in the disordered state that determines the Ms. The insights obtained here can be useful for achieving tailored magnetic properties in alloys through disordering.