Large anomalous Hall angle in the Fe60Al40 alloy induced by substitutional atomic disorder

The electronic and transport properties of the ordered B2-(${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$) phase which undergoes a continuous transition into the disordered A2-(${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$) phase are studied from first principles. The disordering is characterized as a gradual interchange of atoms between Fe and Al sublattices under the condition that the total amount of Fe and Al atoms is kept unchanged. This is the simplest model of gradual disordering of the ordered phase due to the ion irradiation. The physical properties are strongly influenced by varying local environment of Fe atoms on both sublattices. This leads to the transition between a high moment at large disorder and a very low moment in the ordered phase. Similar behavior is found also for anomalous Hall conductivity and anomalous Hall angle. Unusual behavior of the longitudinal conductivity as a function of degree of disorder is due to the shift of the Fermi level of majority states from the $sp$-like part to the $d$ states with increasing ordering. The disordered phase has a large anomalous Hall angle as contrasted with a negligible anomalous Hall angle for well ordered samples, which is in agreement with recent experiment.